Download MR Imaging of the Breast - Hitachi Medical Systems America, Inc.

InsideHMSA
November, 2001
News, Views and Insights From Hitachi Medical Systems America, Inc.
n this issue of Inside HMSA, the
focus is on our Scanogram section that includes techniques,
applications and news of interest for
Hitachi users. Inside you will find a
feature article on breast imaging,
including proper coil selection, pulse
sequences, how to image the augmented
breast versus imaging for breast cancer
and post-processing steps. Another
feature article will detail contrastenhanced MR angiography (CE-MRA),
including step-by-step instructions and
helpful tips on how to successfully
complete this exam.
I
You’ll also find articles detailing how
HMSA assists each customer with ACR
site accreditation, including information about the ACR’s new MRI Quality
Control Program.
For your convenience, we have published
some Web sites where you can find
information about MR safety and also
information about MR educational
and training programs that may be
of interest to you.
See our December issue for comprehensive product information, including
what features were introduced at
RSNA 2001.
MR Imaging
of the Breast
Kathy Hampton, RT(R)(MR)
Education Coordinator-MRI
R Imaging is a powerful tool that
shows promise in evaluating the
breast due to its excellent softtissue contrast and multiplanar capabilities. Unfortunately, it has not been
universally accepted for the diagnosis
of breast cancers and other abnormalities. While the sensitivity is high, the
specificity has been more variable, due
to differences in system software and
image interpretation. MR has shown
its true strength in assessing breast
implant integrity.
M
The number one indication for MR of
the breast is for implant integrity. MR
is the ONLY imaging modality that can
diagnose intracapsular rupture of silicone implants. MR can also help with
staging breast cancer, as well as evaluating the response to radiation or
chemotherapy.1
Good spatial resolution, that is, thin
slices, small pixels, is important, as is
temporal resolution (short scan times).
Both can be achieved on Hitachi systems.
3D imaging is helpful, as it allows for
very thin, contiguous slices and high
signal-to-noise. 3D imaging can be
performed pre- and post-contrast using
an RF Spoiled SARGE (RSSG) pulse
sequence for a T1-weighted acquisition.
Temporal resolution can be achieved
with 2D dynamic imaging. Scan times
can be very short, as a limited number
of slices will be obtained at predetermined intervals.
Coil selection is important for a desirable outcome. A dedicated breast coil
should be the first choice for imaging,
followed by a surface coil. Hitachi
offers a dedicated bilateral quadrature
breast coil, which allows bilateral or
unilateral imaging with high signal-tonoise. Customers can use their large
latchable extremity coil for breast
imaging, however the use of this coil
limits the exam to unilateral breast
imaging.
Regardless of the coil used, it is necessary to properly position the patient
for the exam. The bilateral QD breast
coil offers foolproof positioning of the
coil and patient. First, remove all table
pads, placing the coil directly on the
table. Position the patient prone,
headfirst, making sure that the breasts
are lying in the hollowed out portion
of the coil. It may be necessary to use
the cushions that come with the coil
to fill up any portion of the coil not
occupied by the breast. Place appropriate pads for patient comfort and have
the patient’s arms either alongside the
body or up towards the head. The high
signal-to-noise that this coil offers,
combined with the ability to image
both breasts simultaneously, makes
this coil the best choice for the job.
Continued on page 2
Continued from page 1
Inside
Inside HMSA
Contrast-Enhanced Magnetic
Resonance Angiography
pp. 4-5
Just the FAQ’s
pp. 5-6
ACR MRI Site Accreditation and
MRI Quality Control Program
pp. 6-7
Continuing Education
pp. 7-8
MRI Safety
p. 8
Interested in Authoring
an Article?
p. 8
Quadrature breast coil with patient and coil in
proper position.
If the latchable extremity coil is used,
you can only scan one breast at a time.
To properly position your patient using
this coil, first place the appropriate
table pads on the table so that when
the patient lies down, the breast will
be at isocenter coronally. Next, position
the patient with the affected side
down, arm above the head. Roll the
patient back until she is comfortable,
placing cushions under the back for
support. Next, place the coil adjacent
to the breast, securing it with the table
straps and ensuring that the coil
remains perpendicular to the
magnetic field.
Pulse sequences differ according to the
diagnosis. A study to rule out implant
rupture may include T2 FSE to differentiate between implant and normal
breast tissue and to assess the placement and integrity of the implant.
On a T2- weighted image, silicone has
higher signal intensity than any other
tissue. An Inversion Recovery sequence
to suppress fat (T1 100-110 ms) or silicone
(200-220 ms) is also helpful. A FatSep™
pulse sequence, if the system is
equipped, is also beneficial. The FatSep
acquisition provides the radiologist
with a post-processed fat- and a watersuppressed image. The usual scan
planes are sagittal and axial since
the radiologist may compare the MR
images to previous mammograms.2
The breasts may also be imaged in the
coronal plane. Contrast is normally
not indicated for implant ruptures.
T2-weighted FSE sagittal image acquired with
the latchable extremity coil.
Latchable extremity coil in proper position.
Note that the patient’s anatomy is at isocenter
coronally.
2
A study to rule out suspicious lesions
will utilize a different protocol
altogether. Remember to mark any
palpable mass with a Vitamin E
capsule or MR marker. It is helpful to
start an IV prior to imaging to decrease
the chance of patient motion. Precontrast imaging will most likely
include a T2-weighted FSE, an Inversion
Recovery sequence and a T1-weighted
slice locations and then compared the
contrast enhancement over time.4
Breast imaging may be confusing at
this point. Malignant lesions show
enhancement, but benign lesions may
also enhance. Normal breast tissue
may even enhance if the scan takes
place during the proliferative phase of
the menstrual cycle.3 This is the main
reason why MR of the breast for lesion
detection has not gained wide acceptance. There tends to be many false
positives and some false negatives.
T2-weighted FSE sagittal image of the augmented
breast, demonstrating rupture of the implant.
This exam was done with the QD breast coil.
3D Gradient Echo sequence (RSSG). 3D
acquisitions are a good choice because
they can be reconstructed in any plane
after the exam is complete. Contrastenhanced sequences are usually
indicated. 2D dynamic scanning can
help assess contrast uptake in the
lesion, and it may be helpful to repeat
the 3D RSSG post-contrast sequence.
Along with comparing the MR images
with standard film-screen mammograms, the radiologist may find it helpful to post-process and/or analyze the
images. It may be easier for the radiologist to appreciate an enhancing lesion
if the pre-contrast images are subtracted
from the post-contrast acquisition.
Malignant lesions tend to have irregular
spiculated margins. They tend to
enhance very rapidly, especially along
the edges and then
washout quickly.
Benign lesions that
enhance will have
well-defined borders
and tend to show
slow and progressive
enhancement over
time. There is literature that describes
the rate and pattern
of enhancement of
malignant versus
benign lesions. In
order to “see” these
patterns, the radioT2-weighted FSE TRS image of the breast. Demonstrates intracapsular
logist may place
rupture of the implant.
an ROI over the area
Dynamic imaging of the breast allows
of greatest enhancement2 and then
easy comparison of contrast enhancereview graphs that display the
ment over time. One study repeated
enhancement rates over time. The
T1-weighted acquisitions at 1, 3, and
data, graphically displayed, can
5 minutes post-injection at the same
sometimes aid the radiologist in
3
determining whether the lesion shows
signs of malignancy based on enhancement patterns. Hitachi has included this
analysis software on all of its systems.
There are three types of graphs:
• Time-Intensity Curve (Normalize)
This graph displays the TimeIntensity curve of the differential
value of different ROIs over time.
• Time-Intensity Curve (Ratio)
This graph displays the TimeIntensity curve of the ratio between
the pre- and post-contrast image sets.
• Time-Difference Curve
This graph displays the speed of
enhancement or the time difference
between the pre- and post-contrast
image sets.
Most enhancing lesions in the breast
will not be malignant2, but biopsies
will still be performed for these suspicious lesions. New coil technology,
such as interventional breast coils
for MR biopsy are being investigated,
as are new pulse sequences to help
increase the specificity of MR. As
techniques, software and hardware
improve and evolve, confidence in this
modality should increase.
1
Soo, M, Spritzer, C. MR Imaging of the
Breast. Applied Radiology, p. 18, September
1996.
2
Orel, S. Differentiating Benign from
Malignant Enhancing Lesions Identified
at MR Imaging of the Breast: Are TimeSignal Intensity Curves an Accurate
Predictor? Radiology, p. 1, April 1999.
3
Matzko, J. Contrast-enhanced MR of the
breast: Evolving roles. Applied Radiology,
p. 47, March 1995.
4
Obdeijn, I, et al. MR Lesion Detection in a
Breast Cancer Population. JMRI, p. 850,
November/December 1996.