MRI of the Adrenals, Kidneys,
Bladder, and Prostate
James P. Earls, M.D.
Director of Cardiovascular and Body MRI
INOVA Fairfax Hospital, Falls Church, VA
Assistant Professor of Radiology
Johns Hopkins Medical Institutions, Baltimore MD
Outline signal adds, when out of phase (180 degrees
• MR techniques opposite each other) their signal destructively
• Contrast agents interferes. For this reason fat-water mixtures lose
• Clinical applications signal when out of phase. This signal loss occurs
- Adrenal, Kidney, Bladder, Prostate
with adrenal adenomas, myelolipomas, renal
angiomyolipomas, and adnexal lesions.
A phased-array torso coil is optimally
used to perform GU MRI because it significantly
increases signal and reduces noise in the abdomen.
A combination of routine T1 and T2 weighted
sequences are used for most GU purposes. In
selected cases newer sequences, including ultra-
fast T2 (HASTE, SSFSE) are employed.
Opposed-phase imaging techniques are commonly
used for adrenal lesion characterization. 3D
gadolinium-enhanced MR angiography is useful
for angiographic evaluation of the GU system,
including renal donor and recipients, renal cell
carcinoma evaluation, and other selected cases.
Ultra-fast T2 sequences are heavily T2
weighted and fluid is bright. These provide for
very rapid “MR urograms” that can be performed
during suspended respiration. These can be used
for rapid screening of the bladder, ureters, and
other fluid filled structures.
Opposed-phase imaging is a useful tool
for characterization of certain fat-water
admixtures, such as that which occurs in adrenal
adenomas. Fat and water protons spin at slightly
different frequencies. At predictable time points, Fig 1. An obstructed right ureter is depicted on this coronal
they will be completely “in-phase” or “out of ultrafast T2 weighted image (SSFSE single shot fast spin echo)
acquired in less than 1 second.
phase” with each other. When in-phase, their
Earls, GU MRI
Another technique that is useful as Gadolinium is safe to use in these
indicated above is 3D Gad MR Angiography. This patients. In one study of 342 patients with renal
provides for a very rapid and accurate insufficiency who received both nonionic contrast
angiographic analysis of the arteries and veins of exam and gadolinium (on separate days), a
the abdomen and pelvis. Most scanners can significant rise in serum creatinine was noted after
perform this sequence in approximately 20-30 iodinated contrast, but not after gadolinium.
second. Please refer to the Gadolinium-enhanced (Prince et al, JMRI 1996; 6:162-166). In this study
MR angiography chapter for further information. nephrotoxicity = 5mg/dl serum creatinine increase.
Gad vs. Nonionic contrast; Nephrotoxicity
MR Contrast Agents
Several contrast agents are currently Creatinine Nephrotoxicity
available for MRI. As a whole these agents are change
significantly safer than iodinated agents used for Nonionic + 0.35 mg/dl 17%
CT and other radiographic exams. Gadolinium is
used most frequently for both evaluations of Gadolinium - 0.07 mg/dl 0%
tumor, infection, and angiography. The other two
new agents, ferumoxides and Mn-DpDp, are (Prince et al, JMRI 1996; 6:162-166)
usually used for hepatic imaging.
AGENT MECHANISM USE
MR evaluation of the adrenal glands is
rapid and accurate. MR is more specific than
Gadolinium Extracellular General,
spiral CT for characterization of adrenal
fluid 3D MRA
adenomas. Adrenal MR studies are performed
rapidly and are very specific.
Ferumoxides RES specific Liver lesion
Use of opposed-phase technique with a
single in-phase followed by an out of phase series
takes less than 5 minutes of “table time” and can
Mn-DpDp Hepatocyte HCC, liver
characterize adenomas with a greater than 95%
specificity and sensitivity. Using opposed-phase
techniques, adenomas lose signal intensity by 10%
or more between in and out of phase images. All
Gadolinium can be used safely in patients imaging parameters, except for the TE, must be
with renal insufficiency. It has no reported renal identical (i.e. the same TR, fov, slice thickness,
toxicity. Both ionic and nonionic iodinated gap, bandwidth, flip angle etc).
contrast media have a real risk of producing
In one study (Schwab et al, NEJM 1989;
302:149-153), nephrotoxicity, defined as a 44
mumol/l serum creatinine increase, was evaluated
in 443 patients s/p cardiac catheritization. They
were randomized to ionic or nonionic contrast.
Nephrotoxicity was seen in a substantial number
of patients who received both nonionic and ionic
iodinated contrast agents (see table).
Incidence of Iodinated Contrast Induced
All Patients High Risk
Nonionic 8.2% 15%
Fig 2. An adrenal adenoma is depicted as a low
Ionic 10.2% 17% signal intensity mass on this out of phase T1 weighted GRE
image (FLASH TR 150, TE 2.5, and FA 80).
(Schwab et al, NEJM 1989; 302:149-153)
Earls, GU MRI
Opposed-phase Imaging Technique the histologic composition of masses and other
• Use standard T1-weighted GRE images. The one disadvantage of MR as compared
to CT is the relative insensitivity of MR to small
• Incremental TE change makes the sequence calcified stones in the collecting system or ureters.
in-phase or out-of-phase. Therefore in the evaluation of a potential renal
• Fat and water have different resonance donor, we obtain a plain radiograph to evaluate for
• When imaged “out of phase” fat and water Most commonly, renal MR is doe to
signals interfere destructively. evaluate an indeterminate renal mass seen on
• Used to depict areas of hepatic steatosis and another examination. Patients may be renal
adrenal adenomas. insufficient or have iodinated dye allergies, and
therefore cannot have a CT. Occasionally, a mass
Because the adrenal glands are thin seen on renal-protocol CT is sent for MR
structures, and adrenal lesions may be quite small, evaluation because of an indeterminate CT
thin sections are optimal when performing adrenal reading. Protocol for these studies is pretty
MRI. We normally use 4-mm slices for imaging. simple; we do a T2 FSE in one or occasionally 2
Fat saturation is both useful and can be a planes (axial, or axial and coronal). This is
hindrance. The retroperitoneal fat provides for followed by a pre and dynamic post-contrast t1
good internal contrast and makes the adrenals easy GRE series performed as a breathhold. It is best to
to see, so suppression of the fat with fat saturation use thin slice; 4-5 mm is optimal depending on the
may actually make it more difficult to visualize length of time the patient is able to hold their
subtle abnormalities. However, if one wants to breath. The pre-contrast images can be subtracted
prove that a lesion in the adrenals contains fat, from the post-contrasted images to produce a
then it is best to perform a T1 GRE series with and “subtraction” series. This is excellent for
without fat saturation, any bulk fat containing determination of mass enhancement.
lesions, such as a myolipoma, will lose signal on MR is an excellent tool for evaluating the
the fat-saturated series. renal vascular system, especially the main renal
T2-weighted images are useful when arteries in case of suspected renovascular
evaluating other adrenal lesions, such as cysts, hypertension and for evaluating the renal veins in
hemorrhage, and pheocromcytomas. Therefore as cases of suspected thrombosis or tumor extension.
a standard adrenal protocol, we include T2- Please see the chapter on renal and aortic MRI in
weighted images, even though they are not helpful this syllabus.
for the most common indication for adrenal MRI;
characterization of adrenal adenomas Sample Renal MR Protocol
T2 FSE axial
Sample Adrenal MR Protocol T1 GRE - axial
Pre and Post Gadolinium
GRE T1 axial Optional
In-phase & Out of phase 1. GRE T1 - Opposed phase axial
Optional- 2. 3D MRA coronal
T2 FSE fat sat axial
GRE T1 fat sat axial
Kidneys Bladder imaging is performed less
Renal MR can be thought of in a similar frequently than adrenal or renal MR, but it can still
manner to renal CT, i.e., pre and post contrast provide useful diagnostic information in a number
images are essential for evaluation of the of diagnoses. In our practice, we use dynamic
enhancement of masses to differentiate cysts from contrast enhanced bladder MRI for staging of
solid masses. In addition, T2 pulse sequences and invasive bladder cancer. Cancers typically
fat saturation techniques can be used to evaluate enhance earlier than normal bladder muscle, so an
Earls, GU MRI
arterial phase study is helpful to fully delineate the accuracy of MRI in the local staging of PCa. The
tumor. reported accuracy of MRI in staging prostate
Other bladder applications include the cancer ranges from 54% to 90%. These results
evaluation of uretheral diverticulum in women. have raised concerns about interobserver
We perform T2 weighted sequences in multiple variability and lack of reproducibility. Over the
planes using thin slices with a high matrix to past three years, however, more encouraging
achieve high spatial resolution. results have been obtained for endorectal MRI.
Occasionally we image the bladder with Diagnostic performance has improved with
MR to evaluate for other tumors such as extra- reported accuracy consistently between 75% and
adrenal pheochromocytomas. 90%. Another strength of MRI that has been
identified is its high specificity (> 90%) in
excluding extraprostatic tumor.
The signal intensity and the detection of
PCa depend on the type of imaging sequence used.
On Tl-weighted images, the prostate is of
homogeneous medium signal intensity. On T2-
weighted MR images, prostatic carcinoma most
commonly is shown with decreased signal
intensity within the high-signal-intensity normal
peripheral zone. The detection of PCa on MRI
(similar to TRUS) is applicable only to the tumors
located in the peripheral zone. Even in the
peripheral zone, tumor detection may be hampered
by post biopsy changes. Depending on the time
interval between biopsy and MRI scan, the biopsy
changes may cause either under- or over staging of
Fig 3. Gadolinium is safe to use in patients with renal tumor presence and extent. It has been
insufficiency. Here it enhances a bladder transitional cell CA demonstrated that MRI study should be performed
in a patient with a serum Cr of 3.0 and chronic renal
at least three weeks after biopsy. While PCa
detection rates as high as 92% have been reported,
Prostate the results of large multicenter studies are
disappointingly low, with only 60% of lesions
greater than 5 mm in any one dimension being
The use of diagnostic imaging in staging
detected on MRI scans.
evaluation of Prostate Cancer (PCa) is a subject of
controversy. The recommendations range from
denial to strong advocacy for imaging prior to any
therapy decision. Considering the disagreements
about PCa detection and choice of treatment, the
debate concerning imaging is not surprising.
There are evidence-based guidelines on the use of
imaging in assessing the risk of distant spread of
PCa. The radionuclide bone scan and computed
tomography (CT) supplement clinical and
biochemical evaluation (PSA, prostatic acid
phosphates) for suspected metastatic disease to
bones and lymph nodes. Guidelines for the use of
bone scans (in-patients with PSA > 10 ng/ml) and
CT (in patients with PSA > 20 ng/ml) have been
reported and are in clinical use.
No such consensus exists at the current time
Fig 4. A low-T2 signal intensity area of prostate cancer
for the use of imaging in evaluating PCa local (arrow) is depicted in the peripheral zone of this gland..
tumor extent, specifically on the use of MRI.
Variable results have been found for the diagnostic
Earls, GU MRI
The role of MRI is in the evaluation of depends on the equipment and local expertise
tumor extracapsular and seminal vesicle invasion. available. None of the modalities are perfect, and a
MRI findings of extracapsular extension on judicious combination provides the best results. In
endorectal coil MRI include a) irregular bulge of the staging of PCa, each modality - transrectal US,
the prostate margin, b) contour deformity with MRI and CT - has advantages and disadvantages.
step-off or angulated margin, c) breech of the Evaluation by TRUS is restricted to local staging
capsule with direct tumor extension, d) obliteration only, while both CT and MRI allow detection of
of rectoprostatic angle, and e) asymmetry of local, nodal, and distant metastatic invasion. The
neurovascular bundles. The seminal vesicle role of CT in staging PCa is reserved for the search
invasion is diagnosed when there is a) for lymph node metastasis, evaluation of advanced
demonstration of contiguous low-signal-intensity disease, and planning radiation therapy. MRI
tumor extension into and around seminal vesicles, offers the most complete evaluation of PCa
and/or b) tumor extension along the ejaculatory assessing local, regional and nodal disease. The
duct resulting in nonvisualization of the endorectal coil provides higher staging accuracy
ejaculatory duct, decreased signal intensity of than the body coil. Discrepancies in the opinion on
seminal vesicles, and loss of seminal vesicle wall the value of the endorectal coil attest to the
on T2-weighted images. While transaxial planes immaturity and still developing field of MR
of section are essential in the evaluation of imaging. The combination of MR Imaging and
extracapsular invasion, the invasion of the seminal Spectroscopic imaging offers anatomic and
vesicles is facilitated by the evaluation of metabolic information and appears to be the
transaxial and coronal plane of section. method of the future.
In a recently reported study by Yu et al„
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