DOI:10.2214/AJR.06.0131
AJR 2006; 187:605-608
© American Roentgen Ray Society
Impact of "Cine MR Imaging: Potential for the Evaluation of Cardiovascular Function"
Vincent B. Ho1 and
Thomas K. F. Foo2
1 Department of Radiology, Uniformed Services University of the Health Sciences,
4301 Jones Bridge Rd., Bethesda, MD 20814-4799.
2 MR Imaging Laboratory, General Electric Global Research, Niskayuna, NY
12309.
Received January 23, 2006;
accepted after revision February 1, 2006.
Each month the American Journal of Roentgenology will republish
online one or more of the 100 most-cited articles from its first century. A
corresponding commentary in the print journal by a contemporary radiologist
will provide a current perspective. For a full list of these articles, see
page 3 of the January 2006 issue of the AJR or go to
www.ajronline.org.
The opinions or assertions contained herein are the private views of the
authors and are not to be construed as official or reflecting the views of the
Department of Defense or the Uniformed Services University of the Health
Sciences.
Address correspondence to V. B. Ho
(vho{at}usuhs.mil).
Keywords: cardiac imaging • cardiovascular imaging • cine MRI • MRI • MR technique
In the February 1987 issue of the American Journal of
Roentgenology, Sechtem et al.
[1] reported the exciting
potential application of cine gradient-echo imaging for the functional
evaluation of cardiac disease. On a 1.5-T MR scanner, the technique used an
ECG-gated gradient-echo pulse sequence with TR/TE, 21/12. ECG signal
information and k-space image data were acquired simultaneously and
retrospectively processed for the reconstruction of approximately 20 images
per cardiac cycle. Now widely known as retrospective gating, this technique
was new in the mid-to-late 1980s.
Using this pulse sequence, whole-heart coverage could be achieved via a
stack of 10 to 12 axial cine acquisitions spaced at 10-mm increments. However,
with a single phase-encoding step being performed during each R-R interval,
imaging was necessarily long but achievable within half an hour. Because the
k-space data were acquired asynchronously with the cardiac cycle,
retrospective interpolation had to be performed to re-sort the acquired data
into equidistant temporal positions (images) within the cardiac cycle. The
processing at that time was performed offline and required an additional 30
minutes (5 minutes per cine acquisition for the 5-6 acquisitions required to
image the 10-12 locations). Although primitive by today's standards, this was
a significant accomplishment at the time of the article. The significance of
the Sechtem et al. article is evident by the more than 180 times it has been
cited in the published literature according to a search of the ISI Science
Citation Web database.
In a series of 14 healthy volunteers and 22 patients, Sechtem et al.
[1] described the potential of
using cine gradient-echo imaging to evaluate regional wall motion, ventricular
function (e.g., ejection fraction), valvular function (to include estimation
of regurgitant fractions), and intracardiac shunts—applications that
have now become routine practice for many MR clinics. The gradient-echo
technique afforded bright-blood signal within cardiac chambers for improved
myocardium to blood pool differentiation, which the authors postulated arose
from the superior in-flow sensitivity of the pulse sequence for unsaturated
blood (time-of-flight phenomenon), a hypothesis that is now established dogma.
They also highlighted the ability of the cine gradient-echo pulse sequence to
identify regions of disrupted or turbulent flow as regions of signal loss
(i.e., flow jet) from intravoxel flow dephasing, a characteristic that
continues to be a primary diagnostic tool in screening for valvular
insufficiency or stenosis and for confirming the presence of an intracardiac
shunt or a hemodynamically significant stenosis
[2-4].
The basic principles for cine bright-blood imaging described by Sechtem et
al. have survived the scientific scrutiny of almost 2 decades and have
undergone several improvements as well. In 1991, Atkinson and Edelman
[5] described a more efficient
and faster data acquisition scheme whereby multiple phase-encoded steps were
acquired during each heart beat, namely by the segmentation of k-space data
across fewer cardiac cycles. K-space segmentation drastically reduces the cine
acquisition times such that a single-slice cine acquisition can be performed
during a single breath-hold. Although this development produced a
prospectively gated acquisition of cardiac ventricular motion, improvements in
instrumentation yielded a true segmented k-space technique with retrospective
interpolation and full coverage of the entire R-R interval
[6].
Zerhouni et al. [7] and
Young and Axel [8] introduced
the more advanced method of myocardial tagging for cardiac wall motion by the
placement of a series of radiofrequency saturation bands (or tags) over the
cine images before the initiation of systole. Deformation of the tags over the
cardiac cycle, namely systole, enabled evaluation of myocardial translation
and rotation and the more complex motions associated with cardiac twist. The
lack of tag deformation, moreover, corresponded to a poorly functioning
myocardium.
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Fig. 1A —68-year-old man with aortic insufficiency. (See also Fig.
S1E, video, in supplemental data at
www.ajronline.org)
On cine steady-state free-precession images in three-chamber view (systole,
A; early to late diastole, B-D) a regurgitant flow jet
(arrowhead, B) consistent with aortic insufficiency is seen
during diastole emanating from aortic valve back into left ventricle. Ao =
aorta, LA = left atrium, LV = left ventricle.
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Fig. 1B —68-year-old man with aortic insufficiency. (See also Fig.
S1E, video, in supplemental data at
www.ajronline.org)
On cine steady-state free-precession images in three-chamber view (systole,
A; early to late diastole, B-D) a regurgitant flow jet
(arrowhead, B) consistent with aortic insufficiency is seen
during diastole emanating from aortic valve back into left ventricle. Ao =
aorta, LA = left atrium, LV = left ventricle.
|
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View larger version (150K):
[in this window]
[in a new window]
[as a PowerPoint slide]
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Fig. 1C —68-year-old man with aortic insufficiency. (See also Fig.
S1E, video, in supplemental data at
www.ajronline.org)
On cine steady-state free-precession images in three-chamber view (systole,
A; early to late diastole, B-D) a regurgitant flow jet
(arrowhead, B) consistent with aortic insufficiency is seen
during diastole emanating from aortic valve back into left ventricle. Ao =
aorta, LA = left atrium, LV = left ventricle.
|
|
View larger version (149K):
[in this window]
[in a new window]
[as a PowerPoint slide]
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Fig. 1D —68-year-old man with aortic insufficiency. (See also Fig.
S1E, video, in supplemental data at
www.ajronline.org)
On cine steady-state free-precession images in three-chamber view (systole,
A; early to late diastole, B-D) a regurgitant flow jet
(arrowhead, B) consistent with aortic insufficiency is seen
during diastole emanating from aortic valve back into left ventricle. Ao =
aorta, LA = left atrium, LV = left ventricle.
|
|
More recently, cine imaging has been performed using balanced steady-state
free procession—also known as true fast imaging with steady-state
precession (TrueFISP, Siemens Medical Solutions terminology), fast imaging
employing steady-state acquisition (FIESTA, GE Healthcare terminology), and
balanced fast field echo (Balanced-FFE, Philips Medical Systems
terminology)—in which both the primary gradient-echo is combined with
subsequent refocused echoes to yield increased image signal. This is
accomplished by maintaining a net zero gradient moment for all three physical
axes in each TR interval
[9].
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Fig. 2A —70-year-old man with hypertrophic cardiomyopathy. (See also
Fig. S2E, video, in supplemental data at
www.ajronline.org)
Focal hypertrophy (asterisks) of basal anterior and anteroseptal wall
of left ventricle is noted on diastolic short-axis steady-state
free-precession (SSFP) image.
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Fig. 2B —70-year-old man with hypertrophic cardiomyopathy. (See also
Fig. S2E, video, in supplemental data at
www.ajronline.org)
On cine SSFP images in three-chamber view (diastole, B; early to mid
systole, C and D), thickened basal myocardium
(asterisk, B) is noted to be associated with a flow jet
(arrowheads, C and D) during systole, consistent with
left ventricular outflow tract obstruction.
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View larger version (56K):
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Fig. 2C —70-year-old man with hypertrophic cardiomyopathy. (See also
Fig. S2E, video, in supplemental data at
www.ajronline.org)
On cine SSFP images in three-chamber view (diastole, B; early to mid
systole, C and D), thickened basal myocardium
(asterisk, B) is noted to be associated with a flow jet
(arrowheads, C and D) during systole, consistent with
left ventricular outflow tract obstruction.
|
|
View larger version (140K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 2D —70-year-old man with hypertrophic cardiomyopathy. (See also
Fig. S2E, video, in supplemental data at
www.ajronline.org)
On cine SSFP images in three-chamber view (diastole, B; early to mid
systole, C and D), thickened basal myocardium
(asterisk, B) is noted to be associated with a flow jet
(arrowheads, C and D) during systole, consistent with
left ventricular outflow tract obstruction.
|
|
The steady-state free-precession (SSFP) pulse sequence has a signal
dependence on the tissue T2/T1 ratio and is thus less reliant on blood in-flow
for vascular illustration. This affords improved visualization of both the
endocardial and epicardial borders on SSFP images for wall motion and chamber
size evaluations. These new pulse sequences also have short TR and TE times
(e.g., TR/TE, 2/0.9) that enable quick acquisition times (e.g., 6 seconds) and
even real-time screening examinations. The SSFP method was first described in
the mid 1980s [9]; however, it
has not been until recent technical improvements in instrumentation and
gradient hardware that this technique has gained significant routine clinical
use (Figs. 1A,
1B,
1C,
1D,
2A,
2B,
2C, and
2D and supplemental Figs. S1E
and S2E available at
www.ajronline.org).
SSFP pulse sequences are characterized by short-sequence TR times because of
sensitivity to off-resonance effects and that enables quick cine acquisition
times. The upper limit for TR is determined by the degree of local magnetic
field inhomogeneity.
Cine phase contrast is another technique that in many ways is a derivative
of cine gradient-echo imaging
[10-13].
In cine phase contrast, each k-space acquisition segment is replaced by a pair
of gradient-echo acquisitions that toggles the polarity of a flow-encoding
gradient. This process is repeated over the entire cardiac cycle as in the
cine gradient-echo acquisition. Taking the phase difference between the two
acquisitions yields an image with a phase that is directly proportional to the
velocity and direction of flow, enabling the quantification of blood flow over
the cardiac cycle. Flow quantification in all three directions could be
determined by as few as four flow-encoding experiments per k-space line,
thereby reducing the overall acquisition time using four-point processing
[14]. By the use of similar
k-space improvements, such as segmented k-space acquisition schemes, cine
phase contrast can also now be performed during a breath-hold. Using the
modified Bernoulli equation, this technique also enables the estimation of
flow pressure gradients across regions of luminal narrowing
[3,
15].
Significant improvements have occurred over the nearly 2 decades since
Sechtem et al. [1] described
their promising new technique for cardiac function evaluation using a cine
gradient-echo pulse sequence. Cine MRI is a commercially available technique
that is a fundamental tool of all clinical MR practices. Although the speed
and image quality have developed rapidly, the current development cycle is
rushing toward that of automated evaluation of the large cine MR data sets
that can yield more than 40 images per acquisition location. A variety of
automated segmentation tools are currently available, but most still require
at least some human interaction to provide accurate quantitative measurements
for cardiac function. It is conceivable that these functions will be
completely automated in the near future, enabling the further achievement of a
fuller potential for cine MR evaluations of cardiovascular function.
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