1. CARDIAC MRI
By: Ali Shaikh

2. HISTORY OF MRI

3. Magnetic Resonance Imaging (MRI)
 MRI is a non-invasive imaging technique that came into clinical
use in the early 1980s.
 It is based on the principles of nuclear magnetic resonance (NMR)
that were developed in the 1930s.
 Significant advances were necessary to go from the basic
principles of NMR to generating images of the human body.
 Techniques were developed to localize the small amount of radio
frequency (RF) energy generated from spinning hydrogen protons
when a patient is placed in a strong magnetic field.
 Image production today relies upon magnetic fields created by
superconducting magnets and sophisticated electronics which
manipulate and process the RF energy.

4. Courtesy: http://www.magnet.fsu.edu/educa&on/tutorials/magnetacademy/mri/images/mri-scanner.jpg

5. MRI & the Heart
 MRI has revolutionized medical imaging for many organ
systems.
 However, due to the motion of the heart, the development of
cardiac MRI has been slow as compared to MRI for other
organs due to the requirement for faster acquisition
techniques.
 With advancements in technology, these obstacles have been
overcome and cardiac MRI has become a validated tool for
imaging the heart.

6. WHAT IS CARDIAC MRI?

7. Cardiac MRI
 Cardiac MRI creates
pictures of the heart as it's
beating, producing both
still and moving pictures of
the heart and major blood
vessels
 Doctors use cardiac MRI
to get pictures of the
beating heart and to look
at its structure and
function
 These pictures can help
them decide how to treat
people who have heart
problems
Courtesy: https://jobs.stmarys.org/centers/radiology/mri/images/mri_cardiac.gif

8. Cardiac MRI
Unlike computed tomography (CT) scans and standard X-rays,
MRI doesn't use ionizing radiation or carry any risk of causing
cancer
Cardiac MRI test is used to diagnose and evaluate a number of
diseases and conditions, including:
* Coronary heart disease
* Damage caused by a heart attack
* Heart failure
* Heart valve problems
* Congenital heart defects
* Pericarditis (a condition in which the membrane, or sac,
around the heart is inflamed)
* Cardiac tumors

9. PROGRESS IN CARDIAC
MRI

10. Pulse Sequences
 Pulse sequences are a pattern of radiofrequency pulses and
magnetic gradients that are used to produce an image
 There are a variety of different pulse sequences that are used
in cardiac imaging that can be broadly divided into either
black-blood techniques or bright-blood techniques
 Spin echo (SE) cardiac sequences are typically black-blood
techniques, while gradient echo sequences are typically
bright-blood techniques

11. Black-Blo o d Te chniq ue s
 Spin-echo (SE) was the first sequence used for evaluating
cardiac morphology
 The development of ECG-gating made SE techniques
especially useful by substantially reducing motion artifacts
 SE sequences generally provide good contrast between the
myocardium and blood
 These are called “black-blood” images because of the signal
void created by flowing blood
 Blood signal may appear brighter in slower flowing areas,
such as immediately adjacent to the chamber wall

12. Black-Blo o d Te chniq ue s
 Presaturation with radiofrequency (RF) and reduction of the
echo time (TE) minimizes blood signal and increases contrast
on gated SE images
 SE imaging has limited temporal resolution and is degraded
by respiratory and other motion-related artifacts.
 Shorter acquisition times are achieved with fast SE (FSE)
pulse sequences, also known as rapid acquisition relaxation
enhancement (RARE)
 Soft-tissue contrast may be less optimal than with SE
techniques because of the wide range of acquired TEs
inherent in FSE methods
 Single-shot FSE (SSFSE) sequences use a very long echo
train in tandem with half-Fourier reconstruction

13. Black-Blo o d Te chniq ue s
 In cardiac imaging, the basic SSFSE technique has not
proven to be useful because the long echo trains required
coupled with the relatively short T2 leads to poor image
contrast and blurring
 However, the SSFSE sequence can be modified for better
cardiac
results by reducing the echo train length, lowering the
effective TE, and using a blood-suppressed preparation
method
 T2-weighted inversion recovery (IR) imaging is now used as
the frontline sequence for depiction of cardiac morphology

14. Black-Blo o d Te chniq ue s
 This technique uses a selective and a non-selective 180°
inversion pulse followed by a long inversion time to null blood
magnetization
 A second selective 180° inversion pulse can also be applied
to
null fat. This is referred to as double (DIR) or triple (TIR)
inversion recovery.
 The sequence is acquired with either a breath-hold or a non-
breath-hold technique and provides excellent delineation of
myocardial–blood interfaces

15. Figure 1. Comparison of short-axis views acquired with ECG-gated SE (left) and T2-weighted DIR imaging.
Note that the ventricular blood signal is minimized and that the blood–myocardial interface is more clearly depicted
on the DIR.

16. Brig ht-Blo o d Te chniq ue s
 Bright-blood imaging yields both morphologic and functional
data.
 Blood generates bright signal intensity (SI), and multiple
consecutive images are acquired that can be viewed
dynamically to depict cardiac motion
 Sequences include gradient-recalled echo (GRE), fast GRE
(fGRE), segmented k-space fGRE, and steady state free
precession (SSFP)
 GRE imaging is well suited for cardiac imaging because of its
short TEs and TRs
 Blood appears bright compared to adjacent myocardium due
to time-of-flight effects as well as the relatively long T2

17. Brig ht-Blo o d Te chniq ue s
 A segmented k-space approach provides high-resolution
dynamic images of the heart that are acquired much more
rapidly than prior techniques
 Using short TEs (2 msec) and TRs (10 msec), multiple
lines (segments) of k-space are acquired during each cardiac
cycle.
 The technique is limited by the need to maintain adequate
enhancement of inflowing blood
 The inability to further reduce TR effectively limits achievable
spatial and temporal resolution
 A new approach to improve cine imaging involves a technique
known as SSFP

18. Brig ht-Blo o d Te chniq ue s
 Image contrast in SSFP depends on the T1/T2 ratio of tissue,
and is less dependent on flow compared to the GRE
techniques
 SSFP uses the available blood signal very efficiently and
accurately
depicts blood, myocardium, and epicardial fat
 SSFP sequences result in improved contrast between
myocardium and ventricular cavities, with a clearer delineation
of trabeculation and papillary muscles as compared to
segmented k-space fGRE techniques
 The other advantage of SSFP is improved temporal resolution

19. Figure 2. Comparison of mid-diastolic short-axis views acquired with segmented k-space GE imaging (left) and
SSFP (right). Substantial blood pool heterogeneities are present in the segmented k-space GE image (left) as
compared with the homogeneous blood pool on the SSFP image (right). The SSFP technique has improved
endocardial border definition throughout the cardiac cycle as compared with the older technique.

20. Figure 3. Set of end-diastolic images obtained in a healthy volunteer with a cine 3D SSFP
(FIESTA) sequence within a single breath-hold. The acquisition was acquired with a variable
temporal k-space sampling scheme (VAST), and a 256x192 matrix in a 34-cm FOV with 4-mm
partitions.

21. Myocardial Perfusion
 Myocardial regional blood flow is assessed using dynamic
MRI during the first pass of a contrast agent
 The myocardial territory affected by a coronary artery lesion
may or may not exhibit a perfusion deficit during firstpass
imaging under resting conditions
 However, under pharmacological stress the stenotic vessel is
unable to respond like a healthy vessel because of its higher
vascular resistance, which results in a “vascular steal”
phenomenon with increased blood flow to the territories
supplied by the nonstenotic vessels
 A perfusion deficit appears in the perfused myocardial territory
served by the stenotic vessel

22. Acq uisitio n Te chniq ue s
 Conventional fGRE or fast low-angle single-shot (FLASH)
techniques have been used for the assessment of myocardial
perfusion
 These strategies consist of a data acquisition segment that is
preceded by an IR (180° flip angle) or preparatory
radiofrequency (RF) pulse
 This preparatory pulse generates T1 contrast between the
enhancing normal myocardial tissue and non-enhancing
regions of perfusion deficit
 However, these approaches were limited by acquisition times
of 500–700 msec per image, resulting in only one or two scan
locations every one or two heartbeats
 The long acquisition window degrades image quality, as
cardiac motion results in artifacts and edge blurring.

23. Figure 4. Selected myocardial strain (circumferential shortening, Ecc; lower row) maps obtained with the HARP
technique on conventional tagged MR images (upper row) of a canine heart with a left ventricular pacing. Images
are shown in late diastole (left), early systole (middle), and late systole (right). Blue indicates contraction in the
activated pacing site during early systole (solid arrows) and in the whole myocardium in late systole. Red indicates
stretching opposite the pacing site in early systole (arrowheads).

24. Myocardial Viability
 The ability to differentiate between viable and nonviable
myocardium plays a critical role in the prognosis of patients
with coronary artery disease
 Until recently, thallium SPECT and PET were the primary
tools for this evaluation, with dobutamine stress
echocardiography playing an ancillary but growing role
 In the last few years, however, MRI has made a dramatic
appearance in this arena with the introduction and rapid
acceptance of the delayed enhancement (DE) MRI technique
 This imaging sequence identifies irreversible myocardial
damage in both the acute and chronic settings, and combined
with cine imaging can identify reversibly injured tissue that
may benefit from revascularization.

25. Figure 7. 2D DE-MRI in a patient with chronic ischemic disease of the LAD distribution. A two-chamber long-
axis image (left) reveals thinned tissue with transmural hyperenhancement involving the majority of the anterior
wall and the entire apex, indicating a chronic transmural myocardial infarction. The left ventricular cavity is
dilated and there is apical thrombus (black arrow). Cine images (right) at end-diastole (upper) and end-systole
(lower) demonstrate akinesis of the anterior wall and apex (arrowhead).

26. Figure 8. 3D DE-MRI performed in a patient with a chronic infarction of the LAD distribution.
This series of short-axis images from apex to base was acquired in a single breath-hold and has
image quality nearly comparable to that of 2D images.

27. Coronary MRA (CMRA)
 The coronary arteries have long been known to be one of the
most difficult arterial circulations to image using MRI
 The challenges for CMRA are the inherent complex geometry
and tortuosity of the coronary arteries, their small caliber (2–4
mm), and their continual displacement by respiratory and
cardiac motion
 The wide variety of 2D and 3D CMRA techniques investigated
over the past decade has been testimony to these difficulties

28. Bre ath-Ho ld Te chniq ue s
 In the early 1990s, Edelman et al and Pennell et al reported
successful coronary illustration using a breath-hold fat-
suppressed fast 2D GRE pulse sequence with a segmented k-
space scheme
 A single image was obtained during each breath-hold and
imaging was targeted for diastole, when the heart is less
mobile and coronary flow more brisk
 Subsequent clinical assessments, however, revealed mixed
success with sensitivities for the detection of
hemodynamically significant
stenoses

29. Figure 9. DE-MRI in acute myocardial infarction. The lower images demonstrate DE-MRI (left) and cine images in end-diastole
(middle) and end-systole (right). DE-MRI reveals transmural irreversible damage of the distal septum and apex, while the cine
images reveal corresponding dysfunctional myocardium (arrow). The DE-MRI image in the upper row was performed in the two-
chamber long-axis projection and reveals transmural hyperenhancement of acute irreversible damage in the LAD distribution. Note
the microvascular obstruction (‘noreflow’ or focal nonhyperenhancing regions) in the subendocardium of the anterior wall
(arrowheads), which is associated with greater post-infarction complications and poorer prognosis.

30. Navig ato r-Echo Te chniq ue s
 A novel technique for tracking of “view-to-view” tissue position
using a “navigator” echo
 This technique can be used for prospective or retrospective
gating of free-breathing CMRA
 Navigator-gating CMRA is typically performed using a fat-
suppressed 3D GRE technique

31. Figure 11. Comparison between (a and b) free-breathing navigator-echo gated 2D spiral imaging and (c and d)
breath-held multislice 2D spiral imaging. Image acquisition parameters for all images were: 20-cm FOV, 3.0-mm
section thickness, 2048 20 acquisition matrix, and 70° flip angle. This provided a spatial resolution of
0.96x0.96x3.0 mm for all images. Note that the quality of the free-breathing images (3-minute scan time) was
comparable to that of the breath-held images (19-second scan time).

32. FUTURE OF CARDIAC MRI

33. Predictions
 The acquisition of cardiac MR will become easier
 ECG and respiratory gated sequences will allow high
resolution imaging during free breathing
 Three-dimensional time-resolved images of the heart will
provide images in any desired plane
 ECG gating without leads might become a reality, based on
the automatic detection of cardiac motion
 Perfusion imaging will replace nuclear methods as the gold
standard
 MRI-guided interventions will become available that can
visualise morphology and monitor changes in flow and limb
perfusion during therapeutic interventions

34. Summary of General Trends
Time Frame General Trends
Short term
(Present to 3 Years)
Advances in fast scan techniques (pulse
sequences, RF coils, gradients) will have a
major impact in improving the efficiency and
performance of current exams
lntermediate term
(3 to 5 Years)
- Groups of sequences will be better integrated
into more comprehensive exams
- MR data acquisition will become more
intelligent
Long term
(Beyond 5 Years)
- The clinical role of MRI will expand well
beyond that of diagnosis
- The flexibility of contrast and quantitative
nature of MRI will be further exploited
- The scientific role of MRI will expand,
making it the gold standard for many
applications

35. Conclusions
 Cardiac MRI continues to develop and advance
 The advances include substantial overall improvements in
temporal resolution, spatial resolution, motion and other
artifact reduction, and improved depiction of contrast
enhancement for perfusion and viability analyses
 Its clinical use has been limited, but is increasing because of
its proven clinical efficacy, the proliferation of cardiac-capable
MRI systems, and the development of improved pulse
sequences

36. Resources
 Bremerich, Jens, et al. “MRI: Now and in Future.” 01 Mar 2006.
http://www.hospitalmanagement.net/features/feature645/
 “Cardiac MRI: The Basics.” 2006.
http://www.med-ed.virginia.edu/Courses/rad/cardiacmr/index.html
 Earls, James, et al. “Cardiac MRI: Recent Progress and Continued Challenges.”
Jo urnalo f Mag ne tic Re so nance Im ag ing . 16:111–127 (2002).
 Riederer, Stephen. “The Future Technical Development of MRI.” Jo urnalo f
Mag ne tic Re so nance Im ag ing . 1:52-56 (1996).
 “What is Cardiac MRI.” Jul 2009.
http://www.nhlbi.nih.gov/health/dci/Diseases/mri/mri_whatis.html

37. QUESTIONS