Emission Computed Tomography is a technique where by multi
cross sectional images of tissue function can be produced , thus
removing the effect of overlying and underlying activity. The technique of
ECT is generally considered as two separate modalities. SINGLE
PHOTON Emission Computed Tomography involves the use single
gamma ray emitted per nuclear disintegration. Positron Emission
Tomography makes use of radio isotopes such as gallium-68, when two
gamma rays each of 511KeV, are emitted simultaneously where a
positron from a nuclear disintegration annihilates in tissue.
SPECT, the acronym of Single Photon Emission Computed
Tomography is a nuclear medicine technique that uses
radiopharmaceuticals, a rotating camera and a computer to produce
images which allow us to visualize functional information about a patient‟s
specific organ or body system. SPECT images are functional in nature
rather than being purely anatomical such as ultrasound, CT and MRI.
SPECT, like PET acquires information on the concentration of radio
nuclides to the patient‟s body.
SPECT dates from the early 1960 are when the idea of emission
traverse section tomography was introduced by D.E.Kuhl and
R.Q.Edwards prior to PET, X-ray, CT or MRI. THE first commercial Single
Photon- ECT or SPECT imaging device was developed by Edward and
Kuhl and they produce tomographic images from emission data in 1963.
Many research systems which became clinical standards were also
developed in 1980‟s.
2. Single photon emission computed tomography
What is SPECT?
SPECT is short for single photon emission computed tomography.
As its name suggests (single photon emission) gamma rays are the
sources of the information rather than X-ray emission in the conventional
Similar to X-ray, CT, MRI, etc SPECT allows us to visualize
functional information about patient‟s specific organ or body system.
How does SPECT manage us to give functional information?
Internal radiation is administrated by means of a pharmaceutical
which is labeled with a radioactive isotope. This pharmaceutical isotope
decays, resulting in the emission of gamma rays. These gamma rays give
us a picture of what‟s happening inside the patient‟s body.
But how do these gamma rays allow us to see inside?
By using the most essential tool in Nuclear Medicine-the Gamma
Camera. The Gamma Camera can be used in planner imaging to acquire
a 2-D image or in SPECT imaging to acquire a 3-D image.
How are these Gamma rays collected?
The Gamma Camera collects the gamma rays emitted from the
patient, enabling to reconstruct a picture of where the gamma rays
originated. From this we can how a patient‟s organ or system is
3. THEORY AND INSTRMENTATION
Single –photon Emission Computed tomography or what the
medical world refers to as SPECT is a technology used in nuclear
medicine where the patient is injected with a radiopharmaceutical which
will emit gamma rays. We seek the position and concentration of
radionuclide distribution by the rotation of a photon detector array around
the body which acquires data from multiple angles. The
radiopharmaceutical may be delivered by 1V catheter, inhaled aerosol
etc. The radio activity is collected by an instrument called a gamma
camera. Images are formed from the 3-D distribution of the
radiopharmaceutical with in the body.
Because the emission sources are inside the body cavity, this task
is for more difficult than for X-ray, CT, where the source position and
strength are known at all times.
i.e. In X-ray, CT, the attenuation is measured not the transmission
source. To compensate for the attenuation experienced by emission
photons from injected tracers in the body, contemporary SPECT
machines use mathematical reconstruction algorithms to increase
The gamma camera is made up of two or three massive cameras
opposite to each other which rotate around a centre axis, thus each
camera moving 180 or 120 degrees respectively. Each camera is leadencased
and weighs about 500 pounds .The camera has three basic
layers –the collimator (which only allows the gamma rays which are
perpendicular to the plane of the camera to enter), the crystal and the
detectors. Because only a single photon is emitted from the radionuclide
used for SPECT, a special lens known as a collimator is used to acquire
the image from multiple views around the body .The collimation of the
rays facilitates the reconstruction since we will be dealing with data that
comes in only perpendicular .At each angle of projection, the data will be
back projected only in one direction.
When the gamma camera rotates around the supine body, it stops
at interval angles to collect data. Since it has two or three heads, it needs
to only to rotate 180 or 120 degrees to collect data around the entire body
.The collected data is planar. Each of the cameras collects a matrix of
values which correspond to the number of gamma counts detected in that
direction at the one angle.
Images can be reprojected into a three dimensional one that can be
viewed in a dynamic rotating format on computer monitors, facilitating the
demonstration of pertinent findings to the referring physicians.
4. THE GAMMA CAMERA
Once a radiopharmaceutical has been administered, it is necessary
to detect the gamma ray emissions in order to attain the functional
information. The instrument used in nuclear medicine for the detection of
gamma rays is known as gamma camera(fig 4.1).
Fig. 4.1 Parts of Gamma Camera
The components making up the gamma camera are
1. Camera Collimator
2. Scintillation Detector
3. Photomultiplier Tube
4. Positron Circuitry
5. Data Analysis Computer
4.1 Camera Collimator
The first object that an emitted gamma photon encounters after
exiting the body is the collimator. The collimator is a pattern of holes
through gamma ray absorbing material, usually lead or tungsten that
allows the projection of the gamma ray onto the detector crystal. The
collimator achieves this by only allowing those gamma rays traveling
along certain direction to reach the detector; this ensures that the position
on the detector accurately depicts the originating location of the gamma
4.2 Scintillation Detector
In order to detect the gamma photon we use scintillation detectors.
A Thallium-activated Sodium Iodide [NaI (TI)] detector crystal is generally
used in Gamma cameras. This is due to this crystal‟s optimal detection
efficiency for the gamma ray energies of radionuclide emission common
to Nuclear Medicine. A detector crystal may be circular or rectangular. It
is typically 3/8” thick and has dimensions of 30-50 cm. A gamma ray
photon interacts with the detector by means of the Photoelectric Effect or
Compton Scattering with the iodide ions of the crystal. This interaction
causes the release of electrons which in turn interact with the crystal
lattice to produce light, in a process known as scintillation. Thus, a
scintillation crystal is a material that has the ability to convert energy lost
by radiations into pulses of light.
The basic scintillation system consists of:
2. Light Guide
3. Photo Detector
Fig. 4.2 Basic Scintillation System
4.3 Photomultiplier Tube
Only a small amount of light is given off from the scintillation
detector. Therefore, photomultiplier tubes are attached to the back of the
crystal. At the face of a Photomultiplier tube (PMT) is a photocathode
which, when stimulated by light photons, ejects electrons. The PMT is an
instrument that detects and amplifies the electrons that are produced by
the photocathode. For every 7 to 10 photons incident on the
photocathode, only one electron is generated. This electron from the
cathode is focused on a dynode which absorbs this electron and re-emits
many more electrons. These new electrons are focused on the next
dynode and the process is repeated over and over in an array of
dynodes. At the base of the photomultiplier tube is an anode which
attracts the final large cluster of electrons and converts them into an
Each gamma camera has several photomultiplier tubes arranged in
a geometrical array. The typical camera has 37 to 91 PMT‟s.
4.4 Positron Circuitry
The positron logic circuits immediately follow the photomultiplier
tube array and they receive the electrical impulses from the tubes in the
summing matrix circuits (SMC). This allows the position circuits to
determine where each scintillation event occurred in the detector crystal.
4.5 Data Analysis Computer
Finally in order to deal with the incoming projection data and to
process it into a readable image of the 3D spatial distribution of activity
with in the patient, a processing computer is used. The computer may use
various different methods to reconstruct an image, such as filtered back
projection or iterative construction.
5. SPECT IMAGE ACQUSITIONAND PROCESSING
SINGLE photon emission computer tomography has its goal
determination of the regional concentration of radionuclide with in a
specific organ as a function of time. The introduction of radio isotope TC-
99m by Harpen ,which emits a single gamma ray photon of energy 140
KeV & has a half life of about six hours signaled a great step forward for
SPECT since this photon is easily detected by gamma cameras .
However, a critical engineering problem involving the collimation of this
gamma rays prior to entering the gamma camera have to be solved
before SPECT could establish itself as a viable imaging modality
Single photon emission computed tomography requires collimation
of gamma rays emitted by the radiopharmaceutical distribution within the
body Collimators for SPECT imaging are typically made of lead. They are
about 4 to 5 cms thick and 20 by 40 cm on its side. The collimators
contain thousands of square, round or hexagonal parallel channels
through which – gamma rays are allowed to pass. Typical low-energy
collimators for SPECT weigh about 50 lbs, but high – energy models can
weigh above over 200 lbs. Although quiet heavy, these collimators are
placed directly on top of a very delicate single crystal of a NaI contain
within every gamma camera. Any gamma camera so occupied with a
collimator is called an angle camera after it is invented. Gamma rays
traveling along a path that coincides with one of the collimator channels
will pass through the collimator unabsorbed and interact with the NaI
crystal creating light. Behind the crystal, a grid of photo multiplier tubes
collects the light for processing. It is from the analysis of this light signals
that SPECT images are produced .Depending on the size of anger
cameras whole organs such as heart and liver can be imaged. Large
anger cameras are capable of imaging the entire body and are used, for
example, for bone scans.
For the gamma rays emitted by radiopharmaceuticals typical for
SPECT, there are two important interactions with matter. The first
involves scattering of the gamma ray off electrons in the atoms and
molecules (DNA) within the body. This scattering process is called
Compton scattering. Some Compton scattered photons are deflected
outside the Anger cameras field of view and are lost to the detection
process. The second interaction consists of a photon being absorbed by
an atom in the body with an associated jump in energy level (or release)
of an electron in the same atom. This process is called the photoelectric
effect and was discovered for the interaction of photons with metals by
Einstein, who received the Nobel Prize for this discovery. Both processes
result in a loss or degradation of information about the distribution of the
radiopharmaceutical within the body. The second process falls under the
general medical imaging concept of attenuation and is an active research
Attenuation results in a reduction in the number of photons
reaching the Anger camera. The amount of attenuation experienced by
any one photon depends on its path through the body and its energy.
Photons which experience Compton scattering loose energy to the
scatterer and are therefore more likely to be scattered additional times
and eventually absorbed by the body or wide-angle scattered outside the
camera‟s field of view. In either case, the photon (and the information it
carries about the distribution of the radiopharmaceutical in the body) is
not going to be detected and is thus considered lost due to attenuation. At
14OKeV, Compton scattering is the most probable interaction of a
gamma ray photon with water or body tissue. A much smaller percentage
of photons are lost through the photoelectric interaction. It is possible for
a Compton scattered photon to be scattered into the Anger camera‟s field
of view. Such photons however do not carry directly useful information
about the distribution of the radiopharmaceutical within the body since
they do not indicate from where within the body they originated. As a
result, the detection of scattered photons in SPECT leads to loss of image
contrast and a technically inaccurate image.
Acquiring and processing a SPECT image, when done correctly,
involves compensating for and adjusting many physical and system
parameters. A selection of these include: attenuation, scatter, uniformity
and linearity of detector response, geometric spatial resolution and
sensitivity of the collimator, intrinsic spatial resolution and sensitivity of
the Anger camera, energy resolution of the electronics, system sensitivity,
image truncation, mechanical shift of the camera or gantry, electronic
shift, axis-of-rotation calibration, image noise, image slice thickness,
reconstruction matrix size and filter, angular and liner sampling intervals,
statistical variations in detected counts, changes in Anger camera field of
view with distance from the source, and system dead time. Calibrating
and monitoring many of these parameters fall under the general heading
of Quality Control and are usually performed by a Certified Nuclear
Medicine Technician or a medical physicist. Among this list, collimation
has the greatest effect on determining SPECT system spatial resolution
and sensitivity, where sensitivity relates to how many photons per second
are detected. System resolution and sensitivity are the most important
physical measures of how well a SPECT system performs. Improvement
in these parameters is a constant goal of the SPECT researcher.
Improvement in both of these parameters simultaneously is rarely
achieved in practice.
Since the time a patient spends in a Nuclear Medicine department
relates directly to patient comfort, there exists pressure to perform all
nuclear medicine scans within an acceptable time frame. For SPECT, this
can result in relatively large statistical image noise due to a limited
number of photons detected within the scan time. This fact does not
hinder our current clinical ability to prognosticate the diseased state using
SPECT, but does raise interesting research questions. For example, a
typical Anger camera equipped with a low-energy collimator detects
roughly one in every ten-thousand gamma ray photons emitted by the
source in the absence of attenuation. This number depends on the type of
collimator used. The system spatial resolution also depends on the type
of collimator and the intrinsic (built in) resolution of the Anger camera. A
typical modem Anger camera has an intrinsic resolution of three to nine
millimeters. Independent of the collimator, system resolution cannot get
any better than intrinsic resolution. The same ideas also apply to
sensitivity: system sensitivity is always worse than - and at best equal to
A collimator with thousands of straight parallel lead channels is
called a parallel-hole collimator, and has a geometric or collimator
resolution that increases with distance from the gamma ray source.
Geometric resolution can be made better (worse) by using smaller
(larger) channels. The geometric sensitivity, however, is inversely related
to geometric resolution, which means improving collimator resolution
decreases collimator sensitivity, and vice versa. Of course, high
resolution and great sensitivity are two paramount goals of SPECT.
Therefore, the SPECT researcher must always consider this trade-off
when working on new collimator designs. There have been several
collimator designs in the past ten years which optimized the
resolution/sensitivity inverse relation for their particular design.
Converging hole collimators, for example fan-beam and cone-beam
have been built which improve the trade-off between resolution and
sensitivity by increasing the amount of the Anger camera that is exposed
to the radionudide source. This increases the number of counts which
improves sensitivity. More modem collimator designs, such as half-cone
beam and astigmatic, have also been conceived. Sensitivity has seen an
overall improvement by the introduction of multi-camera SPECT systems.
A typical triple-camera SPECT system equipped with ultra-high resolution
parallel-hole collimators can achieve a resolution (measured at full-width
half-maximum (FWHM) of from four to seven millimeters. Other types of
collimators with only one or a few channels, called pin-hole collimators,
have been designed to image small organs and human extremities, such
as the wrist and thyroid gland, in addition to research animals such as
5.2 COMPUTERS IN RADIOLOGY AND NUCLEAR MEDICINE
Nuclear medicine relies on computers to acquire, store, process
and transfer image information. The history of computers in radiology and
nuclear medicine is however relatively short. In the 1960s and early
1970s, CT and digital subtraction angiography where introduced into
clinical practice for the first time. Digital subtraction angiography used
computers to digitally subtract from a standard angiogram the effects of
surrounding soft-tissue and bone, thus improving the image for diagnosis.
Computed tomography relied on computers to digitally reconstruct
sectional data using various reconstruction algorithms such as filtered
back projection. The work horse of the CT unit was the computer; without
it CT was impossible. SPECT and MRI first began to appear in the late
1970s. Both of these new imaging modalities required a computer. In the
case of MRI, the computer played a major role in controlling the gantry
and related mechanical equipment. In the SPECT case, as in CT, image
reconstruction had to be done by computer. Nuclear medicine‟s reliance
on computers also has its roots in high-energy particle physics and
nuclear physics. Both of these disciplines rely on statistical analysis of
large numbers of photon (or other particle) counts, collected and
processed by a computer.
5.3 IMAGE ACQUISITION
Nuclear medicine images can be acquired in digital format using a
SPECT scanner. The distribution of radionudide in the patient‟s body
corresponds to the analog image. An analog image is one that has a
continuous distribution of density representing the continuous distribution
of radionuclide amassed in a particular organ. The gamma ray counts
coming from the patient‟s body are digitized and stored in the computer in
an array or image matrix. Typical matrix sizes used in SPECT imaging
are 256x256, 128x128, 128x64 or 64x64. The third dimension in the array
corresponds to the number of transaxial, coronal or sagittal slices used to
represent the organ being imaged. A typical SPECT scanner has a
storage limit of 16 bits per pixel.
Once a SPECT scan has been completed, the raw data image
matrix is called projection data and is ready to be reconstructed. The
reconstruction process puts the data in its final digital form ready for
transmission to another computer system for display and physician
The most common algorithm used in the tomographic
reconstruction of clinical data is the filtered back projection method. Other
methods also exist.
1. Data Projection
2. Fourier Transform of Data
3. Data filtering
4. Inverse transform of the Data
5. Back projection
6.1 Data Projection
As the SPECT camera rotates around a patient, it creates a series
of planar images called projections. At each stop, only photons moving
perpendicular to the camera face pass through the collimator. As many of
these photons originate from various depths in the patient, the result is an
overlapping of all tracer emitting organs along a specified path. A SPECT
study consists of many planar images acquired at various angles. The
fig 6.1(a)displays a set of projections taken of a patient‟s bone scan.
Fig. 6.1 (a) Data Projection of Bone Scan
After all projections are acquired, they are subdivided by taking all
the projections for a single, thin slice of the patient at a time. All the
projections for each slice are then ordered into an image called a
„sinogram‟ as shown in fig 6.1(b). It represents the projection of the tracer
distribution in the body into a single slice on the camera at every angle of
Fig. 6.1 (b) sinogram
The aim of reconstruction process is to retrieve the radiotracer
spatial distribution from the projection data is shown in fig. 6.1 (c)
Fig. 6.1 (c) Reconstruction of Sinogram
6.2 Fourier Transform of Data
If the projection sonogram data were reconstructed at this point,
artifacts would appear in the reconstructed images due to the nature of
the subsequent back projection operation. Additionally, due to the random
nature of the radioactivity. There is an inherent noise in the data that
tends to make the reconstructed image rough. In order to account for both
of these effects, it is necessary to filter the data. We can filter it directly in
the projection space, which means that we convolute the data by some
sort of smoothing kernel.
Convolution is computationally intensive. Convolution in tyhr
spatial domain is equivalent to a multiplication in the frequency domain.
This means that any filtering done by the convolution operation in the
normal spatial domain can be performed by a simple multiplication when
transformed into the frequency domain.
Thus we transform the projection data into the frequency space
where by we can more efficiently filter the data.
6.3 Data filtering
Once the data has been transformed to the frequency domain, it is
then filtered in order to smooth out the statistical noise. There are many
different filters available to filter the data and they all have slightly
different characteristics. For instance, some will smooth very heavily so
that there are not any sharp edges, and hence will degrade the final
image resolution .other filters will maintain a high resolution while only
smoothing slightly .some typical filters used are Hanning filter, Butter
worth filter, Low pass cosine filter, ZWeiner filter etc .Regardless of the
filter used, the end result is to display a final image that is relatively free
from noise and is pleasing to the eye. The fig. 6.3 depicts three objects
reconstructed without a filter true (left), without a filter noisy (middle) and
with a Hanning filter (right).
Fig. 6.3 Reconstruction of objects using Filters
6.4 Inverse transform of data
As the newly smoothed data is now in the frequency domain, we
must transform it back into the spatial domain in order to get out the x, y,
z information regarding spatial distribution. This is done in the same type
of manner as the original transformation is done, expect we use what is
called the one dimensional inverse Fourier transform. Data at this point is
similar to the original fig. 6.4 (a) sonogram expect it is smoothed as
shown in fig. 6.4 (b).
(a) inverse transform of the data (b) Sinogram of inverse transform
6.5 Back Projection
The main reconstruction step involves a process known as „Back
Projection‟. As the original data was collected by only allowing photons
emitted perpendicular to the camera face to enter the camera, back
projection smears the camera bin data from the filtered sonogram back
along the same lines from where the photon was emitted from. Regions
where back projection lines from different angles intersect represent
areas which contain higher concentration of radiopharmaceutical,
7. ADVANTAGES OF SPECT
1. Better detailed resolution: superimposition of overlying structures
2. Lesion contrast higher: small deep lesions may be seen as small
differences in radiopharmaceutical distribution and can be
detected. Hence resolution is improved.
3. Localization of defects is more precise and more clearly seen by
the inexperienced eye.
4. Extend and size of defects is better defined.
5. Images free of background.
8. DISADVANTAGES OF SPECT
1. Since lead collimator is used, it introduces defects in scanning.
Only 1out of 1000 photons emitted hits the detector and contributes
to image reconstruction.
2. A blurring effect is caused due to the gamma particles penetrating
the collimator walls and opaque objects.
3. Spatial resolution is limited
4. Attenuation compensation is not possible due to multiple scattering
9. SPECT APPLICATIONS
1. Heart Imaging
SPECT has been applied to the heart for myocardial perfusion
imaging. The following figure is a myocardial MIBI scan taken under
stress conditions. Regions of the heart that are not being per fused will
display as cooler regions.
2. Brain Imaging
This figure is a transverse SPECT image of the brain. The hot
spots present in the right posterior region are seen clearly using SPECT.
SPECT examines cerebral function by documenting regional blood flow
and metabolism. The SPECT and PET imaging modalities are especially
valuable in brain imaging as they make it possible to visualize and
quantify the density of different types of receptors and transporters. The
accurate assessment of the density of receptors or transporters in the
brain structure is quite challenging because of the small size of these
3. SPECT imaging is specially used to differentiate between infarct and
ischemic. Infarct is an area of necrosis in the tissue or the organ
resulting from obstruction of the local circulation by a thrombus or
embolus. Ischemic is a condition of the localized anemia due to an
obstructed circulation. Clinical studies indicate that SPECT is more
accurate at detecting acute ischemia than CT scan.
4. Tumor detection
SPECT can be used to detect tumors in cancer patients in the early
stages itself. Using this slicing method, we can remove any interference
from the surrounding area and detect disfuntionality of organs pretty
easily. The radioactive chemicals will distribute through the body. The
distributions can be traced and compared to that of a normal healthy
body. Since this method is so precise, doctors can detect abnormalities in
the early stages of disease development when it is more curable. SPECT
has been proven alternative to PET in distinguishing recurrent brain tumor
from radiation necrosis.
5. Bone Scans
Bone scans are typically performed in order to assess bone growth
and to look for brain tumors. The tumors are the dark areas seen in the
picture below. The development of SPECT has enhanced the contrast
resolution of bone scans by screening out overlying and underlying
tissue. This results in increased detection and localization of small
abnormalities especially in the spine, pelvis and knees. A bone scan
typically costs about one third to half as much as a CT or MRI.
6. SPECT is superior to other imaging modalities in detecting subtle
instances of Spondylolysis and assessing the degree of injury activity.
SPECT is also used in diagnosing Alzheimer‟s disease, for performing
lung perfusion, abdominal and pelvic scanning and in diagnosing
epilepsy. Radionuclide scans with increased imaging techniques such
as SPECT have become safe well- established and highly effective
diagnostic tools in sports medicine.
10. POSITRON EMISSION TOMOGRAPHY (PET)
The distribution of activity in slices of organs can be obtained in a
more accurate way using PET. In the simplest PET camera two modified
sophisticated cameras called Anger cameras are placed on opposite
sides of the patient. This increases the collection angle and reduces the
collection times which are the limitations of SPECT .In PET,
radiopharmaceuticals are labeled with positron emitting isotopes. A
positron combines rather quickly with an electron. As a result the two
gamma quanta are emitted almost in opposite directions .In PET
scanners, rings of gamma ray of gamma ray detectors surrounding the
patient are used. Each detector interacts electronically with the other
detectors in the field of view. When a photon arrives within a short time
frame, it is clear that a pair of quanta was generated and that these were
created somewhere along the path between the detectors. Conventional
PET tomography makes use of standard filtered back projection
techniques used in computed tomography and SPECT. Three
dimensional PET scanning has increased sensitivity but also noise. But
since higher sensitivity permits lower radiation doses, the use is justified.
PET is used to study the dynamic properties of biochemical
processes. A large part of the biological system consists of hydrogen,
carbon, nitrogen and oxygen. With the help of a cyclotron it is possible to
produce short –lived isotopes of carbon, nitrogen and oxygen that emit
positrons. Examples of these isotopes are 0-15, N-13, and C-11 with half
– lives of 2, 10, and 13 minutes respectively. PET uses electron
collimation instead of lead collimation. Attenuation correction can be more
accurately done in case of PET. The resolution of PET is much better and
uniform than SPECT.
11. COMPARISON OF PET AND SPECT
SPECT imaging is inferior to PET because of attainable resolution
and sensitivity. Different radionuclide is used for SPECT imaging that
emits a single photon rather than positron emission as in PET. Because a
single photon is emitted from the radio nuclides used for SPECT, a
special lens known as a collimator is used to acquire the image data from
multiple views around the body. The use of collimator results in a
tremendous decrease in the detection efficiency as compared to PET. For
Positron Emission Tomography, collimation is achieved naturally by the
fact that a pair of detected photons (gamma rays) can be traced back to
their origin since they travel along the same line after being produced. In
PET, there might be as many as 500 detectors that could „see‟ a PET
isotope at any one time where as in SPECT; there may be only one or
three collimators. New collimators are designed planar in one direction
and concave in other which improves the spatial resolution and reduces
the non – isotropic blur in SPECT , So that the resolution and sensitivity
can be improved much to that of PET .,
Although SPECT imaging resolution is not that of PET, the
availability of new SPECT radiopharmaceuticals, particularly for the brain
and head, and the practical and economical aspects of SPECT
instrumentation make this mode of emission tomography attractive for
clinical studies of the brain. The cost of SPECT imaging is very low
comparing to PET.
SPECT 1. Afford able Price
2. Large clinical practice
1. Limitation of spatial resolution
2. Blurring effect with higher
PET 1. Good spatial resolution 1. Costly
2. Tracers required are of short
half-lives, hence requires
cyclotrons and particle generators
It is reasonable to speculate about a constant by perhaps a slower
rate of increase of clinical applications of SPECT. It is safe to conclude
that SPECT has reached the stage where it will be a valuable and also an
unavoidable asset to the medical world.
SPECT being a nuclear medicine imaging modality , it has all the
advantages and disadvantages of nuclear medicine can be highly
beneficial or dangerous on the application , so is SPECT .In spite of this ,
Today , nearly all cardiac patients receive a planar ECT or SPECT as part
of their work-up to detect and stage coronary artery disease . Brain and
Liver SPECT scans are also a leading application of SPECT. SPECT is
used routinely to help diagnose and stage cancer, stroke, liver disease,
lungs disease and a host of other physiological (functional) abnormalities.
1. Xiaochuan Pan; Chien-Min Kao; Sidky, E.Y.; Yu Zou; Metz, C.E.;
“/spl pi/-scheme short-scan SPECT and image reconstruction with
nonuniform attenuation” Nuclear Science, IEEE Transactions on ,
Volume: 50 Issue: 1 , Feb. 2003 Page(s): 87 -96.
2. R.S.Khandpur, ”Handbook of Biomedical Instrumentation”.
3. Dr .M. Armugam, “Biomedical instrumentation”.
4. Steve Webb, “Principles of Medical Imaging”.
5. John.G.Webster,“Medical Instrumentation, Application and design”.
6. www.nucmed.bidmc.harvard. Edu
1. INTRODUCTION 1
2. SINGLE PHOTON EMISSION COMPUTED TOMOGRAPHY 2
3. THEORY AND INSTRUMENTATION 3
4. THE GAMMA CAMERA 5
5. SPECT IMAGE ACQUISITION AND PROCESSING 9
6. RECONSTRUCTION 15
7. ADVANTAGES OF SPECT 20
8. DISADVANTAGES OF SPECT 21
9. SPECT APPLICATION 22
10. POSITRON EMISSION TOMOGRAPHY 24
11. COMPARISON OF PET AND SPECT 25
12. CONCLUSION 27
13. BIBLIOGRAPHY 28
SPECT, the acronym for Single Photon Emission Computed
Tomography, is a nuclear medicine imaging modality, giving information
about a patient‟s specific organ or body system. The patient is injected
with a radiopharmaceutical, which will emit Gamma rays. The radio
activity is collected by an instrument called gamma camera and the image
is reconstructed. SPECT is used to make three dimensional images of the
heart, to perform brain studies and for skeletal scintigraphy.