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MRI of the Liver

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					MRI Clinical Applications III                                               Joseph Castillo




1       MRI of the Liver

This section introduces a case study to address learning outcomes 1, 2 and 3. Fast scan
imaging, especially T2-weighted sequences are discussed and evaluated. MR images are
evaluated with reference to normal and abnormal pattern recognition. Images related to the
study are presented at the end of the section. The sequences for this case study are
evaluated and have been modified to address the patient’s inability for adequate breath
holding.

Normal MRI Anatomy
The liver occupies the upper right portion of the abdomen, extending in the left
hypochondrium and is the largest abdominal organ. It is wedge shaped, with the base
of the wedge against the right costal margin and the apex in the left hypochondrium.
It is divided into right and left hepatic lobes, with two further small lobes, the
quadrate and the caudate. The liver is generally divided into segments for accurate
localization of liver lesion. The hepatic veins separate the liver in the following
segments (Ross & Bidgood, 1993, Semelka & Mitchell, 1996).

       The left hepatic vein separates segment 2 from segment 3

       The middle hepatic vein separates segments 4 from segment 8 (superior) and
        segment 5 (inferior)

       The right hepatic vein separates segment 8 and segment 5 from 7 (superior)
        and 6 inferior

       The main right portal vein separates segment 8 from segment 5.

       Segment 6 is the part of the liver closest to the right kidney. Segment 4 which
        is the quadrate lobe is separated from segment 2 and segment 3 by the
        falciform ligament.

       Segment 1 which is the caudate lobe, is bordered anteriorly by the left portal
        vein, posteriorly by the inferior vena cava and laterally by the ligamentum
        venosum.

A complex network of parietal and visceral peritoneal reflections surrounds the liver
and forms the perihepatic ligaments that secure the liver to the abdominal wall, the
retroperitoneum and adjacent organs (Low, 2001). The visceral peritoneum is closely
applied to the liver surface, whilst the parietal peritoneum lines the undersurface of


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MRI Clinical Applications III                                                Joseph Castillo


the diaphragm and the anterior abdominal wall. Perihepatic ligaments are formed
where two layers of peritoneum join, connecting the liver to adjacent structures. The
ligaments include the Coronary ligament, Gastrohepatic ligament, hepatoduodenal
ligament and falciform ligament (ibid).

Hepatic ducts drain bile into the gall bladder. The common hepatic duct is often
visible as a low intensity rounded structure in the liver hilus anterior to the portal vein
and lateral to the hepatic artery. The intrahepatic bile ducts are usually not visible
unless dilated. The gall bladder returns different signal intensities with different
weighting. Bile in the gall bladder is hypointense on T1W and hyperintense on T2W
images (Ross & Bidgood, 1993). Further discussion on Biliary MRI is given in
chapter 2.

Liver returns homogenous signal intensity between that of muscle and fat on both
T1W and T2W.           On T1-weighted images the liver returns intermediate signal
intensity similar to that of the pancreas and almost similar to the signal intensity of the
renal cortex. The short T1 relaxation time is due to a combination of high manganese
content within the mitochondria and the large surface area of endoplasmic reticulum
(Mitchell & Semelka, 1996)

On T2-weighted images the liver returns a hypointense signal relative to spleen and
kidneys (Morrin & Rofsky, 2001). With Fat suppression techniques the liver is
slightly hyperintense organ.     The vascular structures which divide the organs in
different segments are clearly depicted as low signal structures on T1-weighted SE
sequences. The falciform ligament is hyperintense on T1W due to its fat content
(Ross & Bidgood, 1993).




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MRI Clinical Applications III       Joseph Castillo




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MRI Clinical Applications III                                             Joseph Castillo


Clinical indications

        Haemangioma

        Benign tumours and tumour like conditions: - Focal nodular hyperplasia,
         Hepatocellular adenoma, Lipomas, Cystadenoma.

        Malignant        tumours:-    Hepatocellular     carcinoma,       Intrahepatic
         cholangiocarcinoma, Angiosarcoma, Hepatoblastoma

        Hepatic metastases

        Focal infectious processes :- Abscess fungal or pyogenic, Echinococcal cyst

        Vascular diseases :- Portal vein thrombosis, portal hypertension, Budd Chiari
         syndrome

        Diffuse disease: - Fatty liver, Hepatitis, Cirrhosis, Haemochromatosis,
         Lymphoma.


Case study 1 – Liver metastases
Liver metastases are the most common malignant lesions of the liver. A common
indication for CT or MRI of the liver is to exclude liver metastases in patients with
known primary malignancy. It is generally accepted that in some neoplasm as in
colorectal lesions survival can be improved by partial hepatectomy if metastases are
localized to three or fewer segments or less than four hepatic metastases (Braga et al,
2002).

Metastases vary substantially in appearance on T1- and T2-weighted images. Borders
are usually irregular but may be sharp. Lesion shape may be round, oval or irregular.
In general, metastases have low signal intensity on T1-weighted images but could be
isointense or hyperintense on T2-weighted images, depending on the T2 relaxation
times of the lesions. Hypovascular metastases are usually isointense on T2-weighted
sequence and include metastases from colorectal cancer, transitional cell cancer and
carcinoid tumours. In contrast, hypervascular metastases have high signal intensity
on T2-weighted images and possess an intense peripheral ring of enhancement
immediately after gadolinium administration. Malignancies that frequently result in
hypervascular liver metastases include renal, leiomysarcoma, and islet cell tumours
(Semelka & Mitchell, 1993).



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MRI Clinical Applications III                                                 Joseph Castillo


As metastases can undergo haemorrhage, they could return a low to high signal on
both T1- and T2-weighted images. Necrosis may return central low signal intensity
on T2-weighted images surrounded by a higher signal intensity of viable tumour.
This is common with colorectal cancer. Melanoma metastases are usually a mixture
of high and low signal intensity on T1-weighted and T2-weighted images owing to
the paramagnetic properties of melanin (Pedro et al, 2002)


Image optimization in MRI of the Liver
The MRI technique used to image the liver is similar to the one in other areas of the
abdomen and pelvis. However, the location of the liver just under the diaphragm and
heart places extraordinarily technical demands on the practitioner.

The main goals of MRI of the liver is detection of lesions, characterization of detected
lesions, assessment of vessel patency, differentiation between vessel and lesion and
control of motion. The achievement of these goals requires disciplined attention
towards choice of pulse sequence, the selected parameters for pulse sequences and
imaging artifacts. This paragraph attempts to review the major techniques used in the
investigation of the liver. There is no right or wrong way for assessing the liver and it
is likely that in a particular patient a combination pulsing sequence will be used.

Scan Plane

Optimal evaluation of the liver includes axial, coronal and sagittal projections. Axial
sections are obtained from the diaphragm to the inferior margin of the liver
(Westbrook, 1999). This view, allows depiction of the major vascular structures that
separate the liver in various segments. The axial plane is standard for all abdomen
and pelvic acquisitions due to its similarity with the axial plane in CT. In addition, as
the abdomen’s diameter is generally greater in the craniocaudal dimension then in the
transverse dimension, the axial view allows some flexibility in manipulating
parameters to acquire a smaller field of view, than that used in the coronal and sagittal
planes (Bidgood & Kraus, 1993). As a result, spatial resolution is increased by using
smaller field of view. In addition flexible use of the rectangular phase of view allows
reduction in scan time which is ideal for breath hold acquisitions.             The main
disadvantage is that TR is increased to cover the liver in one breath hold.

Coronal images are obtained from the anterior abdominal wall to the posterior
abdominal muscles. The area from the iliac crests to the diaphragm is included in the


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MRI Clinical Applications III                                             Joseph Castillo


image. Coronal image is useful for depiction of subdiaphragmatic pathology, disease
in the dome of the liver, and pathology affecting the aorta, inferior vena cava, and
hepatic veins. The coronal view also allows visualization of the kidneys, psoas
muscles and adrenals. When a large field of view is use, the pelvic organs are also
seen. Although using a large FOV may reduces scan time, spatial resolution is also
reduced and is rarely recommended except for localization of large abdominal masses.

Sagittal plane serves to enhance the evaluation of pathology near the dome of the liver
and diaphragm. This view is however not a standard plane and is mainly used in the
pelvis where many structures lie in or near the midline. These structures include the
bladder, prostate, urethra, penis, uterus, retropubic space, retrovesicle space, and
rectouterine pace and will be discussed in chapters 3 and 4.

Coil choice

The choice lies between using the body coil or a phased array coil. The body coil has
a large field of views to visualize the whole abdomen. However, although it provides
a homogenous signal, it has a poor SNR which limits spatial resolution. Compared
with a body coil, phased array coils containing four to six elements provide two- to
fourfold improvement in SNR. This benefit decreases, but is still substantial as one
images deeply situated organs such as the pancreas. The increased SNR allows one to
faster imaging techniques such as breath hold GRE and FSE. A new technology
known a parallel imaging uses the intrinsic sensitivity variation of phased array coils
to speed the process of phase encoding. Two main approaches are used: SMASH
(simultaneous acquisitions of spatial harmonics) or SENSE (sensitivity encoding)
(Sodickson et al, 1999; Pruessman et al., 1999). Except from special phased array
coils no hardware upgrade is required to apply SENSE or SMASH. The improved
rate in data acquisition permits a further twofold reduction in imaging time. This
allows further improvement in spatial resolution along the phase encoding direction
(Keogan & Edelman, 2001).

Pulse sequence

Various pulse sequences are now available, making liver studies a flexible but yet a
challenging exam for the practitioner. Advances in MR hardware and software allow
the practitioner to use rapid acquisition times that could reduce many of the motion




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MRI Clinical Applications III                                               Joseph Castillo


artifacts. Spine echo (SE) and gradient echo (GRE) sequences are used to provide T2
and T1 weighted images.

T2 Weighted imaging

T2 weighted imaging is useful for the detection of focal hepatic lesions that are
hyperintense relative to normal liver parenchyma. Non solid benign lesions such as
cysts or haemangiomas have long relaxation times and return a high signal. Solid
malignant lesions such as hepatocellular and hypovascular metastatic diseases
however have relatively shorter T2 times and care must be taken on the choice of T2
sequence used as seen in the case study.

Conventional T2 spin echo sequence is not used anymore due to long scan time, and
has been entirely replaced by fast spin echo and single shot spin echo. In Fast spin
echo, several k-space lines are acquired per TR and the acquisition time is decreased
according to a factor, known as echo train length, which is equivalent to the number
of phase encoding acquired per TR (Giovanoni et al, 1997).

                   Scan Time = TR x NEX x Phase Encodings/ ETL.

This sequence provide T2 weighted images similar to conventional spin echoes,
except for the high fat signal due to j-coupling and some blurring due to echo train
spacing (Woodward, 2001). This echo train spacing has been improved using strong
gradient systems yielding images with reduced blurring artifacts. Using an echo train
length of 8 rather than 15 reduce the blurring effect (Low et al., 1993).

Non breath hold T2 FSE imaging can be improved using respiratory triggering and fat
suppression. Fat suppression increase image contrast and reduces the blurring and
ghost artifacts from abdominal fat.

At low magnetic field strength scanners fat suppression is difficult to achieve because
of the small absolute frequency difference between fat and water. STIR imaging
provides acceptable diagnostic quality with uniform fat saturation. However STIR is
not specific in its suppression of fat, and the signal from other lesions with a T1 of
150ms may be nulled with STIR imaging. This is of particular concern when one is
assessing patients with melanoma (Morrin & Rofsky, 2001).

In single shot spin echo sequence, half Fourier reconstruction is used to decrease
acquisition time. This sequence acquires just over half of k-space in one echo train.
Because data can be acquired in less than a second, single shot technique is helpful in


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MRI Clinical Applications III                                               Joseph Castillo


patients with irregular breathing. The disadvantage of single shot spin echo include
poor contrast to noise ratio due to magnetization transfer and thus is less sensitive to
detect solid liver lesions (Ichikawa & Araki, 1999). This also applies to FSE when
using high ETL, because the numerous short spaced 180 RF refocusing pulses of
adjacent slices saturate the invisible water pool of short T2 components (Nitz, 2002).
Jeong et al., (2001) showed on a small scale study that the conspicuity of solid liver
lesions may be enhanced on T2W sequence after administration of gadolinium.

Recently, breath hold fast spin echo techniques have been introduced, acquiring T2W
images in less than a minute (Augui et al., 2002). The sequence is a modification to
the fast SE T2W sequence using fast-recovery T2 enhancement and an optimized
section ordering scheme. The breath hold fast recovery technique makes use of
additional radiofrequency pulses after the final acquisition window to drive the
recovery of the longitudinal magnetization. An additional 180 deg refocusing pulse
follows the last echo in an FSE echo train. A -90 deg pulse is then used to drive the
refocused magnetization back up onto the longitudinal axis instead of allowing it to
recover with T1 process.        After an interval of several TR, a steady state of
longitudinal magnetization is established with net enhancement of long T2
components (Nitz, 2002).

Another modification to the above sequence is an optimized slice acquisition scheme.
When multiple acquisitions are used to collect the number of slices, conventional FSE
will acquire slices by default in an interleaved fashion. With this default scheme, if
two acquisitions of 20 sections are required for the liver, the patient will do two breath
holds. The scheme will acquire the odd slices (1,3,5…19) in the first breath hold and
the even slices (2,4,6….20) in the second breath hold. Because it is impossible for a
patient to hold his breath at exactly the same location in each breath hold, there is a
potential risk to miss portions of the liver entirely.

With an optimized acquisition scheme, the acquisitions are acquired in groups of
contiguous slices. Thus if 2 acquisitions of 20 sections are required for the liver this
scheme will acquire the first 10 slices (1,2,3…10) in the first breath hold and from 11
to 20 in the second breath hold. In addition, the two groups may be prescribes with
some overlapping to prevent the possibility of missing tissue between groups of
slices.




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MRI Clinical Applications III                                               Joseph Castillo


This flexibility in T2W sequences creates a dilemma of which sequence to use. It is
suggested that breath hold techniques are best for presenting fewer image artefacts.
But as regard lesion detection, non breath hold technique is superior to breath hold
imaging. The use of single shot sequences is limited to detecting and characterizing
nonsolid lesions with long T2 time (Ichikawa & Akari, 1999). Fast recovery breath
hold techniques were better than breath hold FSE in detecting solid lesion. The T1
contrast inherent in FSE techniques as a result of the stimulated echo contribution to
the signal is attenuated in the fast recovery imaging, using additional pulses at the end
of the echo train (Augui et al, 2002).



T1 weighting imaging

Most hepatic lesions in patients without chronic liver disease show a non specific low
signal on T1-weighted images due to increased free water protons. Fat-containing
lesions like lipomas, adenomas and occasionally focal nodular hyperplasia (FNH)
have a shorter T1 and exhibit a higher signal than normal liver parenchyma. Other
lesions returning a high signal include intralesional haemorrhage, melanin containing
lesions and proteinaceous mucin containing lesions (biliary cystadenoma) (Morrin &
Rofsky, 2001). Fat suppression techniques, including chemical shift imaging (in
phase and out of phase GRE imaging) help to detect intravoxel lipids and thus
confirm macroscopic fat within lesions.

T1 weighted imaging is generally achieved with breath hold GRE sequence or non
breath hold SE sequences. The latter is generally used in scanners which are unable
to acquire breath hold acquisitions. Motion suppressing techniques, including ROPE
and signal averaging is used with SE sequences. Thus GRE T1 weighted sequences
are considered the best technique to assess the liver as the fast scanning allowing
more patient throughput. The sequences make use of in phase TE, a large flip angle
in the range between 70 and 90 and a TR ranging between 100 and 200 (Kamel &
Bluemke, 2003). The TE may also be chosen out of phase to yield out of phase
images. At 1.5T , a GRE sequence with a TE between 4.2 and 5msec results in an in
phase images, whereas out of phase images is obtained using a TE between 2 and
2.8msec. A recent sequence modification allows the simultaneous acquisition of in
phase and out of phase images in multisection mode. Thus respiratory misregistration



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MRI Clinical Applications III                                               Joseph Castillo


between in phase and out of phase images is eliminated while scanning time is
reduced.

Magnetization prepared GRE sequence is another T1 weighted image used to assess
the liver. In this sequence the data acquisition occur during the T1 recovery of tissues
following a 180 degree inversion pulse. The inversion pulse provide flexible image
contrast and may be set either to null blood signal and minimize pulsation artefacts or
assist in the characterization of liver lesions. For example in differentiating between
haemangiomas and cysts the former return a low signal whilst the cysts return an
isointense signal to that of normal liver because the T1 of the fluid is generally longer
than that of haemangiomas (Morrin & Rofsky, 2001). Another use of magnetization
prepared signal is to characterize liver metastases. At a particular inversion time
(TI=600msec), liver metastases return a signal similar to that of spleen.



Use of contrast media in MRI of the liver

The liver may be assessed using paramagnetic contrast agents such as gadolinium
agents, which increase the intensity of normal hepatocytes or superparamagnetic
agents such as superparamagnetic oxides, which decrease the intensity and appears
dark.

To be effective contrast agents should exhibit selective or differential accumulation
within the different tissue compartments being assessed. Gadolinium chelates are
non-specific extracellular contrast agents that rapidly equilibrate between the
intravascular and extracellular spaces after injection. Gadolinium is delivered in the
liver through the hepatic arteries and then by the portal vein, and distributes fairly
rapidly in normal and abnormal tissues. This fast distribution requires rapid imaging
in order to maximise differential enhancement between normal liver parenchyma and
lesions. Using high field scanners, using 2D or 3D SPGR sequences, the whole liver
could be assessed using one breath hold. Increased SNR is achieved using phased
array coil, whilst CNR is improved using fat suppression. During arterial phase, there
is minimum hepatic parenchymal enhancement.             Capillary enhancement of the
pancreas and renal cortex is observer together with a heterogeneous splenic
enhancement. The hepatic arteries and main portal vein branches should return a high
signal but the hepatic veins should not be enhancing.    Because most hepatic tumours



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MRI Clinical Applications III                                                Joseph Castillo


have only a hepatic arterial blood supply, early gadolinium arterial phase are critical
for depicting enhancing hypervascular metastases and hepatocellular carcinoma (Low,
2001).

The portal venous phase images are obtained approximately 60seconds after the
injection of contrast material. During this time, the hepatic parenchyma returns a high
signal, because the portal vein supplies 75 to 80% of the blood to the liver. This
phase will decrease conspicuity of hypervascular lesions as both lesion and normal
tissues are filled with contrast. As most liver tumours are hypovascular relative to the
liver parenchyma, they will be visualized as hypointense lesions relative to the
enhancing liver on the venous phase (Helmberger & Semelka, 2001).

Delayed or equilibrium phases are obtained 3 to 5 minutes after the injection of
contrast media. Most liver lesions becomes less conspicuous on these images, but
some tumours with interstitial space such as cholangiocarcinoma will accumulate
more contrast material than the liver and return a high signal.

Liver specific contrast agents are divided into hepatocyte-selective and kupffer’s cell-
selective contrast agents. The former encompass the chelated compounds MnDPDP
(Teslascan, Nycomed Amersham, Norway), Gd-BOPTA (Multihance, Bracco SpA,
Italy) and Gd-EOB (pending trials), whereas the latter consist of the group of
superparamagnetic iron oxide (Feridex, Guerbert, France) particles.

The hepatocyte-specific contrast agents are ionic metals chelates with a relatively
pronounced hydrophilicity, a weak protein binding and a residual capacity of
lipophilicity.     The Gd formulations, Gd-BOPTA and Gd-EOB-DTPA, enter the
hepatocytes by way of the adenosine triphosphate (ATP) dependent, membrane
bound, multispecific organic anion transporters located in the sinusoidal and
canalicular side of the hepatocytes. Both are cleared rapidly from the plasma with a
varying degree of hepatobiliary elimination.

MnDPDP        is   a    manganese   derivative   demonstrates     a   more   complicated
pharmacokinetic pathway. Its hepatocellular uptake involves a complex process of
dissociation, transmetallization, selective manganese uptake and elimination.

On the basis of the paramagnetic properties of gadolinium and manganese ions, the
above mentioned hepatobiliary contrast agents enhance the T1 signal.




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MRI Clinical Applications III                                               Joseph Castillo


The superparamagnetic iron oxide (SPIO) consists of nanoparticles typically
composed of an iron core of 3 to 5 nm in size. The core is covered with a dextran that
increases the particle size between 50nm and 150nm. After IV administration the
particles are cleared from the plasma by the reticuloendothelial system of the liver
(80%) and spleen (12%). The particles are eliminated in the lymph nodes and bone
marrow. The plasma half life of the nanoparticles is 8 to 10 minutes. Nevertheless
the superparamagnetic effects last for several days, providing an imaging period of
several hours after administration.

The superparamagnetic properties of the iron core are responsible for a significant
disturbance of the local magnetic field around the particles resulting in a pronounced
shortening of both T2 and T1 relaxivity. The principle of contrast enhancement is
based on the presence of kupffer’s cells within the normal hepatic parenchyma, but
these cells tend to be absent in neoplastic lesions of the liver. Thus SPIO particles,
leads to a decrease in signal intensity in tissue containing Kupffer’s cells, whereas a
relative signal enhancement can be observed in tissues devoid of Kupffer’s cells such
as metastases.

Although reticuloendothelial system and hepatocytes selective contrast agents provide
additional functional imaging, they are still unspecific because even malignant
hepatocytes may still possess functioning anion transporters and malignant
hepatocellular adenomas may contain Kupffer’s cells.          On the other hand, the
improvement in gradient systems and modified sequences may enhance a preference
for extracellular contrast agents. In the end, the radiologist must focus on the relevant
clinical information provided by a baseline precontrast imaging.


Artefacts
The main artefact in the upper abdomen is motion due to respiration, bowel peristalsis
and cardiovascular pulsations.        Fast imaging techniques and single shots pulse
sequences in conjunction with breath hold are the most effective techniques to
eliminate respiratory artefacts. This is discussed in page.

Non breath hold imaging can be improved by a variety of techniques used to
compensate for motion artefacts resulting from respiration and cardiovascular
pulsations. These techniques includes signal averaging, respiratory ordered phase-
encoding (ROPE), and respiratory triggering. These will be discussed in Chapter 2.


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MRI Clinical Applications III                                             Joseph Castillo


Spatial pre-saturation pulses placed superior and inferior to the FOV are necessary to
decrease flow motion artefact in the aorta and inferior vena cava (IVC). Gradient
moment nulling (Flow compensation) also reduce flow artefact but increase the
minimum TE it is not used on T1 weighted images.




Patient
An 82 year old lady with previous right hemicolectomy for Dukes C carcinoma was
referred for MRI after CT and Ultrasound examinations showed possibility of Rt liver
metastases.


Patient consideration and equipment
MRI was performed on a GE Signa MR/I (GE, Milwaukee) at 1.5T using a quadrature
phase array coil. The patient completed the metal screening questionnaire and the
receptionist and I confirmed that there were no contra indications to MRI. She was
asked to change into a hospital gown. The patient was very anxious about the
outcome of the exam as she had already done an US and CT scan. In addition she had
passed through a major operation two years previously. I escorted the patient to a
private room and explained the procedure including an estimate of the length of scan
time and the possibility of gadolinium injection. I also informed the patient that the
exam involves several breath holds each of which lasts about 20s. She told me that
she suffers from asthma, but reassured me that she was going to try. The patient was
then escorted into the scan room and asked to lie supine on the scanner couch with her
feet towards the bore of the magnet. She was positioned so that her low thoracic
region was lying over the posterior element of the phased array coil. It was ensured
that middle of the coil was between the xyphoid process and the lower costal margin.
Respiratory gating bellows were applied diagonally around the patient’s abdomen.
Primarily these were applied to monitor and supervise breath hold instructions.
However later these proved indispensable during respiratory triggered sequence as the
case study shows. The breathing waveform was checked and it was regular waveform
with a rate of 18 breath hold per minute. The anterior part of the phase array coil was



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MRI Clinical Applications III                                                Joseph Castillo


placed over the patient’s chest/abdomen opposite the posterior part. A wide Velcro
strap was used to fasten securely the coil. The use of this strap also helps to reduce
respiratory motion artefacts as it limits anterior displacement of the abdomen and
chest. This however must not cause discomfort to the patient in such a way as to
affect breathing.

A panic buzzer was handed to the patient. The vertical laser light was land marked on
the centre of the coil, and the horizontal laser light coinciding to a level between the
xyphoid process and lower costal margin. Once the patient was in the centre of the
magnet, she was asked if she was well and then ear phones were placed over her ears
to protect from gradient noise. Classical music was provided through the headphones
to relax the patient.


Sequence Parameters
The site protocol for liver includes a coronal breath hold T1 SPGR, an axial breath
hold T2 FRFSEOPT and an axial breath hold T1 GRE IR Prepped. As the patient was
unable to hold her breath adequately, axial T1 SE with respiratory compensation,
T2W FSE with respiratory triggering and single shot FSE axial were carried out.
Saturation bands were placed superiorly and inferiorly.

           TR   TE              TI   FA Matrix      NEX ETL FOV THK SAT                   Time
           msec msec
Cor        150      In               90   256x192   1     -     40     8/2       -        22s
SPGR                phase
Ax         -        In    600 30          256x128   1           40     8/2                28s
GRE                 phase
Ax    2000 90                        -    256x224   1           40     8/2       S/I      40s
FRFSE
Ax         90       -                     256x224   4           40     8/2       S/I 4min
FSE                                                                              FAT
RT
Ax T1 800           MIN                   256X128 4             40     8/2       S/I      6min
SE RC




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MRI Clinical Applications III                                               Joseph Castillo


Findings
This is the radiology report “Axial T1 and T2 weighted images were obtained. The
patient had considerable difficulty with breath holding and therefore breathing
independent studies were performed.

…there are multiple lesions present which have characteristic imaging features of
liver metastases. These involve predominantly the right lobe of the liver but there are
lesions present in segment 4 of the left lobe. The largest lesion is present inferiorly in
segment 6…..I also note the presence of multiple nodular lesions at the lung base
especially at the left base, which are highly suggestive of lung base metastases.




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MRI Clinical Applications III        Joseph Castillo




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MRI Clinical Applications III        Joseph Castillo




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MRI Clinical Applications III                                             Joseph Castillo


Critical Evaluation
The images from the breath hold sequences were of undiagnostic value due to
respiratory motion artefact. Incidentally, the respiratory bellows showed that the
patient had a constant and regular breathing waveform. Consequently T1 and T2 FSE
non breath hold sequences were set up. Both sequences used an NEX of 4 to average
out respiratory artefacts. This technique increased the sequence scan time up to
8minutes for the T1 and 6 minutes for the T2. In addition the T1 sequence was run
with respiratory compensation (respiratory ordered phase-encoding) and the T2 FSE
was run with respiratory triggering and fat suppression. The use of fat suppression
helped to reduce further the ‘ghosting’ as fat now is dark and thus less susceptible to
respiratory motion. Both sequences were of excellent diagnostic quality and showed
multiple lesions.      In addition both sequence showed an unfortunate lung base
metastases. Incidentally, the single shot fast spin echo although provided good organ
delineation failed to show the lesions.         The reason is due to blurring and
magnetization transfer effect from the long echo train. Another possible reason is that
fat suppression was not used with the single shot.

As the patient had considerable difficulty in breath holding, dynamic contrast
enhanced imaging was not carried out.          However, the IR prepped breath hold
sequence provided enough information that the lesions were not cystic or
haemangioma.

Comparing the main protocol carried out in this UK MRI centre to that in Malta, there
are various points worth mentioning. In Malta, abdominal imaging is still based on
ultrasound and CT scan because the T2W FRFSEopt breath hold sequence and the
Dual in phase/out of phase sequence are unavailable and so the exams are somewhat
too long when compared to CT. The few abdominal scans that were carried out over
the last thee years are not enough to optimize the protocol for the various diseases
affecting the liver. The outcome of this first hand experience in the UK show that
MRI of the liver is extremely complex and require a team effort made up of
radiologists, surgeons and radiographers to set up protocols that cover the major
diseases affecting the liver.




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MRI Clinical Applications III                                               Joseph Castillo


Treatment and Prognosis
In Western Europe and the United States, the incidence of colorectal cancer is
approximately 400,000 new cases per year. In up to 30% of the patients, metastases
localized to the liver will develop. If the liver metastases are left untreated, patients
have poor prognosis, with a 5-year survival estimated at 3% or less and the results of
treatment with systemic chemotherapy or radiation therapy are poor.

Some of these patients may have resectable disease and surgical treatment with partial
hepatic resection offers the potential for cure. Over the past few years, surgical
management have resulted in a 5 year survival rates of 25% to 44% among patients
who underwent partial hepatic resection.

The basic principle of partial hepatic resection is to remove all anatomically
respectable lesions leaving liver tissue that is free of disease and enough to allow
normal hepatic function (Ruers & Bleichrodt, 2002). Other treatments for
unresectable liver tumours include chemotherapy, chemoembolization, percutaneous
ethanol injection therapy, radiofrequency ablation, crytherapy, microwave ablation,
and interstitial laser coagulation and liver transplant. The role of imaging is to select
patients that fall into the resectable category and eliminate unnecessary radical
surgery in those likely to gain only a short term benefit. Apart from this MR imaging
is also an excellent method to evaluate the liver after resection, systemic and local
tumour therapies. It permits early recognition of complications and the presence of
recurrent tumour, providing a plan to repeat treatment or use alternative treatment
(Braga et al., 2002)


Alternative Imaging Modalities.
At most imaging centres, CT remains the principal imaging modality for the
assessment of liver metastases and extrahepatic disease in patients who are being
considered for partial hepatic resection. The reason for this is that CT is faster and
easily accessible (Kinkel et al., 2002). The use of multidetector CT allows precise
imaging during three distinct phases of hepatic enhancement. Acquisition timing is as
critical as that in MRI and if the scan is started too early an intended phse is missed.
In addition the major drawbacks are the increased radiation dose and the vast amount
of images generated (Ji et al, 2001). Functional imaging with fluoro-2-deoxy-D-
glucose (FDG) positron emission tomography (PET) is emerging as a useful tool in


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MRI Clinical Applications III                                             Joseph Castillo


the management of patients with colorectal cancer and with liver metastases.
Although this technique is not widely available, when compared with other
conventional imaging, FDG PET has been shown to help in the identification of
unexpected foci of tumour tissue and influenced management in 27% of patients
(Zealley et al., 2001). Unfortunately, this technique is expensive and still not easily
accessible.

Ultrasound, although could identify and to some extent characterize solid from cystic
lesions is highly operator independent and is usually used to detect the incidental
lesion. Ultrasound is generally followed by CT scan and MRI for further evaluation.




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MRI Clinical Applications III                                          Joseph Castillo




References:
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Bidgood W.R, & Kraus B.B (1993) Technique (In: Abdominal Magnetic Resonance
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Braga L, Semelka R.C, Pedro M.S, de Barras N, (2002) Post-Treatment Malignant
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Ji H, McTavish J.D, Mortele K.J, Wiesner W, Ros P.R, (2001) Hepatic Imaging with
Multidetector CT, Radiographics,21:71-80.



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of North America, 41(1):51-65.




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MRI Clinical Applications III                                           Joseph Castillo


Keogan M.T, & Edelman R.R, (2001) Technologic advances in Abdominal MR
Imaging, Radiology, 220:310-320.

Kinkel K, Lu Y, Both M, Warren R.S, Thoeni R.F, (2002) Detection of Hepatic
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encoding for fast MRI. Magnetic Resonance in Medicine, 42:952-962.




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MRI Clinical Applications III                                             Joseph Castillo


Ruers T, & Bleichrodt R.P, (2002) Treatment of liver metastases, an update on the
possibilities and results, European Journal of Cancer, 38(7):1023-1033.



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Sodickson D.K, Griswold M.A, Jakob P.M, (1999) SMASH imaging, Magnetic
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Zealley I.A, Skehan S.J, Rawlinson J, Coates G, Nahmias C, Somers S, (2001)
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hepatic disease with FDG-PET, Radiographics, 21:55-69.




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