Mission Possible Reducing Radiation Dose in CT

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					Topic

                                                       X-ray



                                                                                                   X-ray off
                                            UFC                                                                                         t




                                                       Light                          X-ray on


                     1994               1997                   1999           1999                 2002              2005


                     CARE               UFC                    Adaptive       HandCARE             Pediatric         DSCT
                     Dose4D                                    ECG-                                80 kV
                                                               Pulsing                             Protocols
Siemens‘
Dose Saving          Up to   68 %       Up to   30 %           Up to   50 %   Up to   70 %         Up to   50 %      Up to   50 %
features




Mission Possible: Reducing
Radiation Dose in CT
Over the past decade, Siemens has been a pioneer in creating a host of inno-
vative technical features that significantly reduce radiation exposure in CT
scans. SOMATOM Sessions recently requested feedback on some of the most
important of these innovations from physicians in Germany and the U.S.A.
who have had experience with them.

By Catherine Carrington




Lots of people talk about radiation dose    cols that together have cut patient radia-     Applications for Siemens Healthcare in
and CT. But for more than a decade,         tion exposure to a fraction of what it         Forchheim, Germany. “CT is the imaging
Siemens Healthcare has made dose re-        once was.                                      modality of choice in many situations,
duction a mission. The result: an impres-   “Reducing radiation dose has always been       and it would be used even more if not for
sive portfolio of innovations in scanner    a concern for Siemens,” says Thomas            the concern about radiation dose.”
hardware, software, and imaging proto-      Flohr, PhD, Director of CT Physics and         Siemens’ focus was intensified in the late


6 SOMATOM Sessions · November 2009 · www.siemens.com/healthcare-magazine
                                                                                                                                                      Topic


                                                                Selective
                                                                                                                    X-ray off
                                        Dose Shield             Photon
                                                                Shield




                                                                         80 kV              140 kV
                 Dose Shield                                        Attenuation B           Attenuation A           X-ray on


2007             2007                2008                       2008                    2008                2008                2009


Adaptive         Adaptive            Flash                      Selective               4D Noise            X-CARE              Iterative
Cardio           Dose                Spiral                     Photon                  Reduction                               Reconstruction in
Sequence         Shield                                         Shield                                                          Image Space (IRIS)

1–3 mSv Cardio   Up to   25 %        < 1 mSv Cardio             No dose penalty         Up to   50 %        Up to   40 %        Up to   60 %

                                                  < 1 sec




                                                                                                                                        Image
                                                                                                                                    Image data data       Image
                                                                                                                                                        Image
                                                                                                                                      reconrecon        correction
                                                                                                                                                      correction
                                                                         Vol
                                                                                                                                   Compare
                                         Tube 1     Tube 2

                                                                                                                                          Master
                                                                                                                                          recon




       1990s, when the company began to                     spiral cardiac CT scans, ECG-pulsing              ■ 2008: Introduction of the SOMATOM
       systematically search for new ways to                maintains nominal tube current only               Definition Flash CT scanner. With dual
       reduce radiation dose. A timeline shows              during targeted phases of the cardiac             detectors and a table speed of up to
       not only how relentless Siemens has                  cycle, markedly reducing tube current             45 cm/s, the Flash cuts radiation dose
       been in pursuing this goal over the years,           during phases that will not be used for           for coronary CT angiography to less than
       but also how creative Siemens Research               image reconstruction. Dose savings:               1 mSv in many patients.
       & Development was. Key milestones in-                30% to 50%.                                       ■ 2008: Introduction of X-CARE, organ-
       clude:                                               ■ 2005: Introduction of the SOMATOM®              based dose modulation that reduces out-
                                                            Definition Dual Source CT scanner,                put of the X-ray tube when it is directly in
       ■ 1994: Introduction of DOM, later                   which offers further dose efficiencies            front of the breast and other dose-sensi-
       extended to CARE Dose4D, a fully auto-               in cardiac CT through faster scanning,            tive organs, such as the thyroid gland and
       mated, real-time, anatomical dose                    Adaptive ECG-Pulsing, and automated               eye lens. Reduces radiation dose to the
       modulation technology that reduces                   adaptation of table speed to heart rate.          breast by 30% to 40%.
       radiation dose, depending on the area                Dose savings: up to 50%, compared to              ■ 2009: Introduction of Iterative
       of the body, by 20% to 68% – without                 single source CT.                                 Reconstruction in Image Space (IRIS).
       degrading image quality.                             ■ 2007: Introduction of the Adaptive              By “cleaning up” image noise, iterative
       ■ 1997: Introduction of an ultra-fast                Cardio Sequence, a prospective ECG-               reconstruction makes it possible to
       ceramic (UFC) detector designed with a               triggered “step and shoot” technique              reduce radiation dose by up to 60% and
       new gadolinium-oxy-sulfite scintillator.             that reduces the average dose for CT              still produce high-quality images.
       The UFC detector – still a key component             coronary angiography to about 2.5 mSv.            Several dose-reduction strategies de-
       of multidetector and Dual Source CT                  ■ 2007: Introduction of the Adaptive              serve special attention, including CARE
       systems – cut radiation dose by 30%                  Dose Shield, a technique of asymmetric            Dose4D, the Adaptive Dose Shield, the
       when compared to previous generations                collimator control that eliminates over-          SOMATOM Definition Flash CT scanner,
       of CT detectors.                                     scanning at the beginning and end of              and IRIS. Each of these is an example not
       ■ 1999: Introduction of ECG-pulsing, a               the CT spiral. Depending on the length            only of Siemens’ commitment to mini-
       technique that synchronizes tube current             of the scan, it reduces dose by 5% to             mizing radiation exposure but also its
       to the electrocardiogram. Used during                25%.                                              track record of innovation.


                                                                               SOMATOM Sessions · November 2009 · www.siemens.com/healthcare-magazine      7
Coverstory




                                              “With children, you want as low a dose as possible
                                               but also excellent spatial resolution. CARE Dose4D
                                               allows us to reduce radiation exposure in all three
                                               planes without impairing diagnostic image quality.”
                                               Marilyn J. Siegel, MD, Professor of Radiology and Pediatrics at the Mallinckrodt Institute of
                                               Radiology, Washington University School of Medicine, St. Louis, Missouri, USA




CARE Dose4D                                   is particularly important in efficiently             need a lower dose than average-sized
Determining the right tube current and,       reducing dose in the shoulder and pelvic             patients, but they have less fat and less
therefore, the right radiation dose, has      region, where the lateral attenuation is             tissue contrast, which would result in
always been crucial, says Marilyn J.          much higher than the anterior-posterior              noisy images if the dose were too low.
Siegel, MD, Professor of Radiology and        attenuation.                                         Therefore, during real-time dose modula-
Pediatrics at the Mallinckrodt Institute of   Siemens has further refined this process             tion, CARE Dose4D reduces radiation dose
Radiology, Washington University School       with CARE Dose4D. Clinical experience                less than might be expected for smaller
of Medicine, St. Louis, Missouri, USA.        has shown that the relationship between              patients, while increasing the dose
But achieving that goal was much more         optimal tube current and patient size is             less than might be expected for larger
difficult before CARE Dose4D, because         not linear. Larger patients clearly need a           patients. This maintains excellent diag-
adjustments in tube current had to be         higher dose than average-sized patients,             nostic image quality while achieving an
made empirically.                             but they also have more body fat, which              optimal radiation dose.
“CARE Dose4D has really been a great          increases tissue contrast. Smaller patients          “CARE Dose4D is different from dose
advantage for a number of reasons,”                                                                modulation approaches used by other
Siegel says. “We get great image quality,                                                          vendors,” says Flohr. “It uses measured
reduced dose, and increased patient                                                                attenuation data in real time, not just
comfort. And it’s automated, so it’s                                                               information from topograms; it makes
easier for the technologist.”                                                                      use of a wide mA-range; and it can fine-
CARE Dose4D automatically adapts radi-                                                             tune dose on the fly.”
ation dose to the size and shape of the                                                            Nowhere is CARE Dose4D more impor-
patient, achieving optimal tube current                                                            tant than in pediatric imaging, where
modulation in two ways. First, tube                                                                the risk associated with radiation expo-
current is varied on the basis of a topo-                                                          sure is many times higher in children
gram, by comparing the actual patient                                                              than in adults. A child’s smaller body
to a “standard-sized” patient. As might                                                            absorbs more of the radiation dose than
be expected, tube current is increased
                                               “There’s more and more                              does a larger body. In addition, the can-
for larger patients and reduced for small-      awareness about the                                cer induction risk is higher in children,
er patients. Differences in attenuation         amount of radiation                                because they have a longer lifespan
in distinct body regions are taken              used for CT scanning.                              ahead of them. At the same time,
into account. For example, in an adult                                                             because children’s anatomy is smaller it
patient, 140 mAs might be needed in             Siemens has thoroughly                             can be more difficult to visualize.
the shoulder region, whereas 55 mAs             looked into this and is                            “With children, you want as low a dose as
would be sufficient in the thorax,              one of the first vendors                            possible but also excellent spatial resolu-
110 mAs in the abdomen, and 130 mAs                                                                tion,” explains Siegel. “CARE Dose4D
in the pelvis.
                                                to implement the tools                             allows us to reduce radiation exposure in
In addition, real-time angular dose             we need to improve our                             all three planes without impairing diag-
modulation measures the actual attenu-          scanning.”                                         nostic image quality, and that’s key.”
ation in the patient during the scan and                                                           Publications in scientific journals have
adjusts tube current accordingly – not           Christoph Becker, MD, Professor of Radio-         shown that in adults, CARE Dose4D
only for different body regions, but also        logy and Section Chief of CT and PET/CT at        reduces radiation dose by 68% in the
                                                 Munich University Hospital in Germany
for different angles during rotation. This                                                         cervical spine, 37% in the lumbar spine,


8 SOMATOM Sessions · November 2009 · www.siemens.com/healthcare-magazine
1

                                                                                                                                               Topic
X-ray dose

                                                                                                                           Scan with
                                                                                                                           constant mA


                                                                                                                           Reduced dose
                                                                                                                           level based on
                                                                                                                           topogram




                                                                                                                           Real-time
                                                                                                                           angular dose
                                                                                                                           modulation



                                                                                                       Slice position

            1600 mA




              20 mA


                                                                                 mAs for constant image noise
                                              180

                                              160

                                              140
                                                                                                                    CARE Dose4D

                                              120    Quality ref.
                                                     mAs
                                              100
                                        mAs




                                               80

                                               60

                                               40

                                               20
                                                                      75 kg reference patient
                                                0
                                                       200   400 600    800 1000 1200 1400 1600 1800 2000

                                                                                                 Body Size (lo/l)



     1 Instead of just taking into account the patient’s external dimensions and apparent size, CARE Dose4D analyzes the cross-sectional anatomy
    in real-time and adjusts the emitted X-ray dose accordingly – providing excellent image quality with minimized exposure.




                                                                    SOMATOM Sessions · November 2009 · www.siemens.com/healthcare-magazine         9
Coverstory




                                                 opens and closes collimators at the be-       thanks to an innovation unique to the
                                                 ginning and end of each scan, tempo-          SOMATOM Definition Flash, the patient
                                                 rarily blocking those parts of the X-ray      table no longer slowly inches forward
                                                 beam that are not used for image recon-       during scanning. Instead, in low-dose
                                                 struction. As a result, only the targeted     Flash Spiral mode, the table can glide
                                                 tissue is irradiated. Like many other dose-   along at 45 cm/s while the scanner
                                                 saving innovations, it is a feature pio-      integrates data from both detectors,
                                                 neered by Siemens.                            achieving a gap-free scan even though
                                                 “There’s more and more awareness              each spiral is wide open.
                                                 about the amount of radiation used for        Still, according to Hausleiter, the key
                                                 CT scanning,” says Christoph Becker, MD,      question is whether excellent image
                                                 Professor of Radiology and Section Chief      quality can be achieved at such a high
                                                 of CT and PET/CT at Munich University         scan speed and low dose. With the
 “This ultra-low dose was                        Hospital in Germany. “Siemens has thor-       SOMATOM Definition Flash, the answer
                                                 oughly looked into this and is one of the     is clearly yes. “This ultra-low dose was
  never possible before,
                                                 first vendors to implement the tools we       never possible before, but with this scan-
  but with SOMATOM                               need to improve our scanning.”                ner – with its high temporal resolution
  Definition Flash – with                         At Munich University Hospital, Becker         and improvements in the X-ray tube and
  its high temporal reso-                        has two Siemens scanners equipped with        detector – it is now possible,” he says.
                                                 an Adaptive Dose Shield, the SOMATOM          Of the first 100 coronary CT scans per-
  lution and improve-                            Definition AS+ and the SOMATOM                formed on the Definition Flash at the
  ments in the X-ray tube                        Definition Flash. Although the Adaptive       German Heart Center, more than 70%
  and detector – it is now                       Dose Shield reduces the radiation dose in     could be done in Flash mode. As a result,
                                                 every study, the savings are especially       the average radiation dose for all coro-
  possible.”                                     notable over shorter scan ranges. Dose        nary CT scans – including longer scans
  Jörg Hausleiter, MD, Cardiologist, Associate   savings can reach 25% or more in cardiac      needed for presurgical evaluation and
  Professor of Medicine, German Heart            imaging, for example.                         triple rule-out studies – dropped from a
  Center, Munich, Germany                        The Adaptive Dose Shield is especially        median of 5 to 7 mSv down to 1.8 mSv.
                                                 well suited to pediatric imaging. “In any     Of the 70% of patients scanned in Flash
30% in the thorax, and 38% in the abdo-          circumstance in which children have to
men and pelvis. In pediatric scans of the        be investigated, I would always prefer to
heart, a 58% dose reduction has been             use a scanner with the Adaptive Dose
reported for CARE Dose4D.1                       Shield,” Becker says. “It’s always on, and
                                                 it always reduces the radiation dose.”
Adaptive Dose Shield
In spiral CT, it is routine to do an extra       Flash
half-rotation of the gantry before and           At the German Heart Center, Jörg Haus-
after each scan, fully irradiating the           leiter, MD, has been using a SOMATOM
detector throughout, even though only            Definition Flash CT scanner since April.
part of the acquired data is necessary.          With this revolutionary scanner, he can
As a result, the wide-cone beam exposes          image the heart in a quarter of a single
tissue that will never be part of recon-         heart beat. Equally impressive, he has
                                                                                                “With Siemens Iterative
structed images. Until recently, no one          been able to achieve a radiation dose of
gave much thought to this needless radi-         1mSv or less in a large proportion of           Reconstruction I can
ation exposure to patients. Such “over-          patients undergoing CT coronary angio-          save up to 60% dose
scanning” beyond the targeted scan               graphy. “That’s unbeatable compared to          for wide range of rou-
range was simply accepted as an in-              other CT scanners,” says Hausleiter, an
evitable part of spiral CT.                      Associate Professor of Medicine at the
                                                                                                 tine applications while
Siemens took a fresh look at the problem         Munich-based hospital.                          maintaining excellent
and, in 2007, introduced the Adaptive            The SOMATOM Definition Flash gets its           image quality.”
Dose Shield, a technology based on pre-          name from its flash-fast speed. Equipped
cise, fast, and independent movement             with two detectors, two X-ray sources,          Joseph Schoepf, MD, Department of
of both collimator blades. Instead of ex-        and a gantry that rotates in 0.28 sec-          Radiology, Medical University of South
                                                                                                 Carolina, Charleston, USA
posing patients to unnecessary radiation,        onds, the scanner boasts a temporal
the Adaptive Dose Shield asymmetrically          resolution of just 75 ms. Moreover,


10 SOMATOM Sessions · November 2009 · www.siemens.com/healthcare-magazine
2A                                                      2C

                                                                                                                                         Topic




2B




  2 Pediatric imaging: no breath hold and no anesthesia was necessary for the scan with 0.37s scan-time by using only 1 mSv (Fig. 2A);
  Split-second thorax scan by using only 1.65 mSv (Fig. 2B and 2C).



mode, approximately half could be                we can achieve today is one-tenth of              raises the possibility of using CT for
scanned at 100 kV. (In general, a tube           what it was in the PROTECTION I study.            screening patients at risk for heart dis-
voltage of 100 kV is suitable for patients       That’s a major improvement.”                      ease. “We need to start thinking about
with a body mass index of less than 30           Such a low radiation dose could expand            that question,” Hausleiter says. “With
or a body weight of less than 90 kg). In         CT’s horizons in the evaluation of heart          coronary CTA, we would gain informa-
these patients, Hausleiter found that the        disease. For example, for patients with           tion on calcification, the location of
median radiation dose was just 1 mSv.            high heart rates and irregular heart              plaques, and the presence of noncalci-
The other half of the patients were              rhythms, the “step and shoot” Adaptive            fied plaques – the type we really worry
scanned at 120 kV, and received a radia-         Cardio Sequence, with prospective ECG-            about. In the end, screening could
tion dose of 1.6 to 1.8 mSv, still far lower     triggering and arrhythmia detection, is           reduce the number of heart attacks.”
than the typical radiation dose for coro-        ideal and keeps radiation dose to about
nary CT angiography.                             2.5 mSv. For patients with reasonably             Iterative Reconstruction
The PROTECTION I study highlights how            low and stable heart rates, the Flash             Iterative reconstruction, which Siemens
much progress has been made. In 2007,            Spiral is the method of choice. But even          is slated to debut at the 2009 RSNA meet-
Hausleiter and an international group of         for patients with mild arrhythmia,                ing in Chicago, is the latest success story
researchers from 50 medical centers set          Hausleiter thinks the Flash mode, which           in the company’s mission to reduce radia-
out to determine the typical radiation           captures all necessary data in a single           tion dose. Essentially, iterative reconstruc-
dose for patients undergoing coronary CT         heart beat, may be fast enough to do the          tion introduces a correction loop in the
angiography, using CT scanners manufac-          job, and at a radiation dose of 1mSv.             image generation process that cleans up
tured by a variety of vendors. Published in      And, if that one heart beat happens to            artifacts and noise in low-dose images.
the February 4, 2009, issue of JAMA, the         be an extra unwanted beat generated by            Other vendors are working on iterative
study showed that the median dose was            the arrhythmia, the Flash’s low radiation         reconstruction, but Siemens has
12 mSv.                                          dose means there is little risk in repeating      developed a unique method. A typical
“It’s important to realize the large steps       the study.                                        approach to iterative reconstruction is to
we’ve taken,” says Hausleiter. “The dose         A radiation dose of below 1 mSv also              measure data in the reconstructed image


                                                                SOMATOM Sessions · November 2009 · www.siemens.com/healthcare-magazine       11
Coverstory




3                                                                                                        and compare it to the original data, using
                                                                                                         differences to identify ways to improve
                                                                                                         the image. This approach is time-consum-
                                                                                                         ing because, with each iteration, new
                                                                                                         measurement data must be calculated.
                                                                                                         Siemens instead takes the original data
                                                                                                         and reconstructs a super-high-resolution
                                                                                                         image. The image is very noisy, because
                                                                                                         the filtering that ordinarily reduces image
                                                                                                         noise is not used, in order to avoid any
                                                                                                         loss of information. Then prior knowledge
                                                                                                         of the scanned object is used to smooth
                                                                                                         the image and reduce noise within homo-
                                                                                                         geneous regions, while contrast edges
                                                                                                         are preserved. This process is repeated
                                                                                                         over several steps, or iterations.
                                                                                                         “Why is Siemens’ approach better?
                                                                                                         Because we start with a super-high-
                                                                                                         resolution image and clean it up,” says
                                                                                                         Thomas Flohr. “We can fine-tune the
                                                                                                         process, so we don’t lose object informa-
                                                                                                         tion. We maintain image texture that is
                                                                                                         familiar to readers, so the resulting
                                                                                                         image looks like a standard CT image
                                                                                                         and doesn’t have the plastic-like look that
     3 Image cardio sequence: Fully flexible X-ray pulsing in combination with 75ms                      is often the drawback of other iterative
    temporal resolution results in low dose cardio scan (0.36 mSv dose).                                 reconstruction approaches. And the pro-
                                                                                                         cess is very fast and efficient.”

4A                                                                              4B




    4 Image data reconstruction of an abdominal scan with Standard FBP at full dose (Fig. 4A) and scanned at 60% lower dose while reconstructed
    with Iterative Reconstruction in Image Space (Fig. 4B). Despite the fact that Fig. 4B was acquired at significantly lower dose it shows the same low
    noise compared to the standard FBP at full dose.



12 SOMATOM Sessions · November 2009 · www.siemens.com/healthcare-magazine
5
                                                                   5 Single Source CT requires slow-
                                                                  er table feeds to prevent gaps in
                                                                  the acquired volume (top, center).
                                                                  Dual Source CT combines the data
                                                                  from 2 detectors for faster table
                                                                  feeds above a pitch of 3 (bottom).




                              Vol     pitch 1




                              Vol     pitch >1




                              Vol     pitch 3.4
       Tube 1   Tube 2



6
    Conventional Sequence                                          6 When fully flexible X-ray pulsing
                                necessary dose
    Dose                                                          meets 75 ms of temporal resolution,
                                inefficient dose
                                                                  the result is the Flash Cardio
                                                                  Sequence, the most versatile low
                                                                  dose cardio scan on the market. It´s
                                                                  an intelligently triggered sequence
                                                                  that shuts off radiation in the
                                Low dose                          systolic phase when not required and
                                no function                       dynamically reacts to irregularities
                                                                  during the ECG-trace. For the first
    Dose                                                          time, a step and shoot mode is
                                                                  robust and fast enough to freeze the
                                                                  heart and visualize the coronary
                                                                  arteries even at high heart rates,
                                                                  thus allowing even low dose
                                                                  cardiac CT without the need for beta-
                                High dose                         blockers. Additionally the Flash
                                with function                     Cardio Sequence introduces the
                                                                  Siemens-only dual-step pulsing, that
                                                                  maintains a low dose level during
                                                                  the systolic phase to calculate ejec-
    Flash Cardio Sequence                                         tion fraction in addition to coronary
    Dose                                                          imaging. Therefore, the never before
                                                                  possible combination of low dose
                                                                  coronary imaging and functional
                                                                  information now becomes a reality.



                                Low dose
                                with function




                            SOMATOM Sessions · November 2009 · www.siemens.com/healthcare-magazine        13
                                                        7

Coverstory




    CT Radiation Dose                                                  Theoretical Iterative Reconstruction

    in Perspective
    No one would argue that radiation ex-
    posure is unimportant in CT. But as
    dose levels fall, and the risk of induc-
    ing cancer shrinks, it’s reasonable to
    take a fresh look at the risk-benefit




                                                                        Fast Image Data Space
    ratio associated with CT scanning.
    First, it’s important to know that esti-
    mates of the long-term risk of devel-
    oping cancer from radiation exposure
    are based on studies of atomic bomb                                                                                             Exact image
    survivors. Such studies have a high
                                                                                                                                     correction
    level of statistical uncertainty at
    the low radiation doses associated
    with CT.
    The most commonly cited estimate of
    the additional lifetime risk of dying
    from cancer is 0.05% per 10 mSv of
                                                                                                                                       Full raw
    radiation exposure. Not only do many                                                                         Raw data
    CT scans today deliver far less than                                                                                                 data
                                                                        Slow Raw Data Space


                                                                                                                  recon
    10 mSv, but natural background radia-                                                                                             projection
    tion, which is unavoidable, is about
    2 to 3 mSv. In addition, the average
    lifetime risk of dying from cancer in
    western society is about 25% – which
    means that after a 10 mSv CT scan,
    the risk goes up by 0.05% to 25.05%.                                                                          Compare
    By comparison, the lifetime risk of
    dying from heart disease is about
    40%. Decisions about whether to eat
                                                                                                Dose reduction or image quality improvement
    a healthy diet, quit smoking, and get
    regular exercise are likely to have a                                                       Well-established image impression
    substantial cumulative impact on                                                            Very time-consuming reconstruction
    longevity. Which makes you wonder:
    Just how safe is it to eat a double                   7 To accelerate the convergence of the reconstruction IRIS applies the raw data re-
    cheeseburger?                                        construction only once. During this newly developed initial raw data reconstruction
                                                         a so called master image is generated that contains the full amount of raw data in-




Most important, Siemens’ iterative             Future Directions                                             or the more conventional 120 kV proto-
reconstruction technique can reduce            The next automated tool for dose re-                          col. Reported at the 2009 American
radiation dose by up to 60%, depending         duction is likely to be automatic kV                          College of Cardiology Annual Scientific
on the body region and the original scan       adaptation to the patient’s size and the                      Session, the study showed that the use
dose. “With Siemens Iterative Recon-           examination type. Researchers are                             of 100 kV reduced radiation dose by
struction I can save up to 60% dose for        beginning to understand and further                           31%, while image quality scores were
wide range of routine applications while       evaluate its effect on image quality                          virtually identical. “This proves you can
maintaining excellent image quality”           and dose. In the PROTECTION II study,                         use 100 kV very liberally when looking
says U. J. Schoepf, MD, Professor of           for example, Hausleiter and his                               at the coronary arteries,” says Hausleiter.
Radiology and Cardiology and Director          colleagues randomly assigned 400                              At the Mallinckrodt Institute, Siegel
of CT Research and Development at the          patients to undergo coronary CT angio-                        has also been evaluating the radiation
Medical University of South Carolina.          graphy with either a 100 kV protocol                          savings possible through use of a lower


14 SOMATOM Sessions · November 2009 · www.siemens.com/healthcare-magazine
                                                                                                                                                                     Topic




Statistical Iterative Reconstruction                                          Iterative Reconstruction in Image Space




                                                                               Fast Image Data Space
 Fast Image Data Space




                                                           Basic image                                                   Image data                 Exact image
                                                            correction                                                     recon                     correction


                                                                                                               Compare


                                                               Basic
                                            Raw data                                                                        Master
                                                             raw data
     Slow Raw Data Space




                                                                               Slow Raw Data Space

                                             recon                                                                          recon
                                                            projection




                                            Compare



                           Dose reduction                                                              Dose reduction or image quality improvement
                           Fast reconstruction with few parameters                                     Well-established image impression
                           Unfamiliar and plastic-like image impression                                Fast reconstruction in image space

formation. The following iterative corrections known from true iterative reconstruction are consecutively performed in the image space. In addition,
the noise texture of the images is comparable to standard well-established convolution kernels. The new technique results in artifact and noise reduc-
tion, increased image sharpness and dose savings up to 60% for a wide range of clinical applications.




tube voltage. Her work with Lucite                        continue her research in pediatric                        “We’ve already disproved that, and
phantoms that simulate the size of                        phantoms and in patients with this                        we intend to further disprove it.”
various body regions in children has                      newer generation scanner to determine
shown that at a tube voltage of 80 kV                     the impact on radiation dose and
the radiation dose is reduced when                        image quality of modulating kV.
compared to a tube voltage of 140 kV,                     She anticipates that with this newer-                     Medical writer Catherine Carrington holds a
even when the tube current is increased                   generation scanner, the quality of                        master’s degree in journalism from the University
to ensure good image quality.                             CT studies will improve even further                      of California Berkeley and is based in Vallejo,
                                                                                                                    California.
At the St. Louis Children’s Hospital,                     as radiation dose is decreased.
Siegel has been using the SOMATOM                         “There is an old saying, ‘Beautiful                      1
                                                                                                                       Mulkens et al.: Use of an Automatic Exposure Control
                                                                                                                       Mechanism for Dose Optimization in Multi-Detector
Definition AS 64-slice CT scanner                         pictures come at the cost of higher                          Row CT Examinations: Clinical Evaluation, Medical
to scan pediatric patients. She will                      radiation dose,’ ” Siegel says.                              Physics.



                                                                     SOMATOM Sessions · November 2009 · www.siemens.com/healthcare-magazine                               15