Cardiac MRI

D R . N A J E E B U . S O F I
L P S I N S T I T U T E O F C A R D I O L O G Y
Cardiac MRI

?
 Unlike other modalities, MRI offers the capability to modulate both the emitted
and received signals so that a multitude of tissue characteristics can be
examined and differentiated without the need to change scanner hardware.
 As a result, from a single imaging session, one could obtain a wealth of
information regarding
 cardiac function and morphology,
 myocardial perfusion & viability,
 hemodynamics,
 large vessel anatomy.
 CMR is now considered the gold standard for the assessment of regional and
global systolic function, myocardial infarction (MI) and viability, and the
assessment of congenital heart disease.

1 . H I S T O R Y
2 . B A S I C P R I N C I P L E S
3 . H A R D W A R E
4 . I M A G I N G M E T H O D S
5 . G A T I N G
6 . C O N T R A I N D I C A T I O N S A N D S A F E T Y I S S U E S
7 . A P P L I C A T I O N S
8 . N O V E L C M R I M A G I N G T E C H N I Q U E S
Contents

Basic Principles of MRI
&
Equipment

 T 1 A N D T 2 W E I G H T E D I M A G E S
 I M A G I N G S E Q U E N C E S
 B L O O D T E C H N I Q U E S
D A R K B L O O D
B R I G H T B L O O D
 I M A G I N G P L A N E S
Imaging Methods

 Pulse sequences are software programs that drive the scanner with
specific operational parameters and optimal settings.
 An Image is said to be ‘Weighted’ to a certain property.
 That property is the primary determinant of signal intensity in the
image.
 Image contrast is generated by difference in that property.
 Pulse sequences are adjusted to emphasize differences in tissue T1 and
T2, which may be inherent or altered by the presence of contrast media.

T1 & T2 Weighted Images
 Relaxation involves 2 main Components:
1. T1 Relaxation : Z vector will slowly Regenerate
2. T2 Relaxation : New transverse vector will Degenerate rapidly
 Degeneration occurs faster than Regeneration , So T2 is Shorter than T1
 T1 & T2 are tissue dependent.
 Free water molecules will lose energy very slowly as compared to big
molecules which offers less space for nuclei to tumble freely without
collisions.
 Adding Gadolinium contrasts makes relaxation faster.

 An individual pulse sequence is a combination of radiofrequency
pulses, gradient field switches, and timed data acquisitions,
all applied in a precise order, that results in either accentuation or
suppression of specific biological parameters.
 A simple way to conceptualize pulse sequences is to consider them as
consisting of two separate elements:
1. Imaging engine is a required component that provides information regarding
the spatial relationship of objects within the imaging field (i.e, it is the main
component that produces the image).
2. Modifiers are optional components that can be added to the imaging engine
either individually or in combination to provide specific information regarding
tissue characteristics or to speed imaging.

Dark Blood & Bright Blood Images

CMR Planes of Imaging
For the core examination,
1. Short Axis (2 Chamber): short-axis stack from the mitral valve
plane through the apex
2. Long Axis ( 2 Chamber)
3. 4 Chamber ( Horizontal Long Axis)
In general, the slice thickness is 5 to 6 mm.

1 . S C O U T I N G
2 . F U N C T I O N & V O L U M E S
3 . P E R F U S I O N A T S T R E S S & R E S T
4 . V I A B I L I T Y A N D & I N F A R C T I O N
5 . A D D I T I O N A L
1. Morphology
2. Flow/velocity
3. T2 weighted edema imaging
CMR Examination

Function & Volumes
 Cine MRI using GRE or SSFP Imaging Engine.
 Captures a movie of the beating heart in order to visualize its contractile
function.
 20 & 25 cine frames are acquired per cardiac cycle, with each frame comprising
35 to 45 ms.
 Single-shot mode or via a segmented k-space data acquisition approach
 Slices 5-6 mm.
 Highly accurate & reproducible in the measurement of ejection fraction,
ventricular volumes, and cardiac mass.
 In recent years, cineMRI has become widely accepted as the gold standard
for the measurement of these parameters.
 Moreover, it is also increasingly used as an end point in studies of left
ventricular remodeling and as a reference standard for other imaging
techniques.

Perfusion at Stress & Rest
 Movie of the transit of contrast media (typically gadolinium-based) with the blood
during its initial pass through the left ventricular (LV) myocardium (first-pass
contrast enhancement).
 4 to 5 short-axis views are obtained every heartbeat
 Total of 40 to 60 heartbeats consisting of the entire first-pass
 Patient then partially pulled out
• Adenosine 140 mcg/kg/min
• Patient returned after 2 minutes
• Gadolinium contrast administered (0.075-0.10 mmol/kg)
• After contrast clears from LV myocardium adenosine stopped (total 3 - 3.5 mins)
 15 minutes for contrast to wash out from blood pool
 Rest perfusion scan
 Additional gadolinium contrast (0.075-0.10 mmol/kg) 4ml/s
 Delayed enhancement imaging
 After 5 minutes
 Total duration ~ 45 minutes

Viability & Infarction
 Myocardial viability and infarction are simultaneously examined using
the technique known as delayed enhancement MRI (DE-MRI).
 Gadolinium cannot penetrate intact sarcolemmal membrane
 Injured myocytes take up gadolinium and increased tissue
concentration
 Chronic infarction, interstitial space is increased
 High tissue concentrations of gadolinium leads to shortened T1
relaxation times
• Infarct - bright/hyperenhanced
• Viable - black/nulled

Flow & Velocity
 Velocity encoded cine imaging (VENC-MRI), phase contrast velocity
mapping
 Signal from moving blood or tissue will undergo a phase shift relative to
stationary tissue if a magnetic field gradient is applied in the direction
of motion
 Cine loop across cardiac cycle - pixel intensity proportional to blood
velocity
 Grayscale - White maximum in one direction, black maximum in the
other direction

T2 Weighted Edema Imaging
 Necrotic myocardium - tissue water content increases markedly.
 Longer intrinsic T2 for infarcted myocardium (60-65 ms) compared
with that of normal (45-50 ms).
 Uses
 Chronic lesions vs recent onset
 Possible role in identifying myocardium at risk
 STIR, when used in conjunction with DE-MRI, could accurately
distinguish acute (<2 weeks) from chronic MI (>4 weeks) in >90% of
cases.

 Rapid and complex motion of heart and pulsatility of great vessels due
to normal contractility causes technical difficulty .
 Effects of Respiratory motion further complicate cardiac imaging.
 Tackled by implementation of :
1. ECG Gating
2. Respiratory Gating
3. Breath holding Techniques
4. Rapid high performance gradients

 Gating of White Blood images allows for the evaluation of dynamic
Cardiac function and physiology throughout Cardiac Cycle. Examples
include motion of the Myocardium and valve leaflets. Images are
typically reviewed in cine form.
 Gating in Black Blood images serves to time image acquisition during
the diastolic Phase of the Cardiac cycle, thereby limiting Cardiac
motion artifact.

Contraindications and Saftey Issues

1. Absolute Contraindication:
Ferromagnetic Cerebrovascular Aneurysm Clips
Choclear Implants
Hydrocephalus shunts
2. Strong Relative Contraindication:
Permanent Pacemaker
AICD
3. Interval of 6 weeks is recommended in:
Cardiac Occluder Devices
Embolization Coils with weakly ferromagnetic material
Old Vena cava filters
4. Safely Scanned:
Prosthetic Heart Valves
Sternal Wires
Joint replacement
Dental Implants
Retained Epicardial Pacing leads
Annuloplasty Rings
Coronary Stents

Nephrogenic Systemic Fibrosis
 Fibrosing disorder seen only in Renal Failure patients.
 Estimated incidence is 1-7 % in those with eGFR <30ml/min/m2
 Marked expansion and fibrosis of the dermis in association with CD34
+ fibrocytes.
 Systemic Involvement: Muscles, Lungs, Heart.
 Chronic Unremitting course.
 Course:
28% - No improvement ;
20% Modest improvement;
28% death

81
Non-pitting edema with blister and bullae
Peau d’orange skin changes
Cobblestoning and induration skin Contracture

1 . C A D
2 . C M P
3 . A R R Y T H M I A S
4 . P E R I C A R D I A L D I S E A S E S
5 . C H D
6 . V A L V U L A R H E A R D I S E A S E
7 . T H R O M B U S A N D M A S S
Applications

1 . D E T E C T I N G & Q U A N T I F Y I N G M Y O C A R D I A L I S C H E M I A
2 . A S S E S S M E N T O F M Y O C A R D I A L V I A B I L I T Y
3 . M Y O C A R D I A L I N F A R C T I O N
CAD

1.Detecting and quantifying myocardial ischemia
 Appreciation of LV myocardial ischemia has traditionally depended on
identifying abnormalities after experiencing some form of stress of
1. LV myocardial perfusion,
2. wall motion,
3. metabolism,
4. or epicardial coronary artery blood flow
 CMR is unique in that with a single imaging modality one can identify
abnormalities of LV myocardial perfusion or wall motion in a single test
with a relatively high spatial resolution and without administration of
any form of ionizing radiation.

 Based on multimodality appropriate use criteria, stress CMR is
considered appropriate for patients with high pretest probability for
coronary artery disease (CAD) or intermediate pretest probability of
CAD with an uninterpretable ECG or inability to exercise.
 It is also appropriate for patients with an abnormal ECG who are
intermediate to high risk as well as those with an abnormal or
uncertain exercise ECG or those with obstructive CAD of uncertain
significance noted on computed tomography (CT) or invasive coronary
angiography.

Dobutamine Stress Test
 For Dobutamine stress testing, baseline images are acquired in three standard long-axis
and short-axis views at rest.
 Dobutamine (in increasing doses up to 50 μg/kg/min) and atropine are then infused to
achieve a heart rate response that is 85% of the maximum predicted heart rate response
for age.
 Optionally at intermediate stages, repeat wall motion images may be obtained.
 At peak stress or at the first sign of chest pressure consistent with angina, repeat wall
motion and myocardial stress perfusion images are acquired
 The pharmacologic stress agents are then discontinued, and a recovery series of images is
obtained. To interpret the test, the LV is divided into 17 segments .
 The sensitivity and specificity of dobutamine stress CMR for detecting greater than 50%
coronary arterial stenoses with wall motion analyses alone range from 78% to 96%.

2. Contractile Reserve and Viability

 Although LGE techniques are widely used for identifying myocardial scar and
thus infer viability, dobutamine stress CMR measures of LV myocardial
contractile reserve remain important for assessing myocardial segments that
have the potential to recover systolic function after successful epicardial
coronary arterial revascularization.
 After baseline imaging, Low-dose dobutamine infusions in the range of 7.5
to 10 μg/kg/min are administered and repeat assessments of myocardial
contractility are obtained.
 Dobutamine stress CMR has a similar diagnostic accuracy relative to 8F-
fluorodeoxyglucose PET scanning.
 A particular advantage of low-dose dobutamine infusions for assessing
myocardial viability is that they can be administered to patients with reactive
airways disease as well as those with renal dysfunction in whom the use of
gadolinium may be contraindicated.

Vasodilator Stress
 CMR perfusion imaging in general is accomplished after the administration of
contrast agents that help to demonstrate discrepancies in LV myocardial
perfusion between adjacent myocardial segments as well as absolute perfusion
within a particular segment.
 Although intravenous Adenosine or Dipyridamole has traditionally been
administered to accomplish vasodilator stress, Regadenoson has been
utilized in the CMR environment as well. This agent is beneficial for the study
of those individuals with obstructive or reactive airways disease in that
regadenoson will enhance endothelial independent vasodilation of the coronary
microcirculation but not precipitate bronchial constriction associated with lung
disease.

 The stress perfusion protocol includes a stress perfusion assessment, followed
by evaluation of LV wall motion, rest perfusion, and LGE identification of
myocardial injury/fibrosis. Utilizing this methodology, the sensitivities and
specificities for identifying flow-limiting coronary arterial stenosis when
compared to contrast coronary angiography have both exceeded 90%.
 The overall sensitivity and specificity of CMR vasodilator perfusion tests for
identifying flow-limiting coronary artery stenosis were 91% and 81%,
respectively.

Algorithm for detection of CAD

3.MYOCARDIAL TISSUE CHARACTERIZATION
 The most widely used imaging method for identifying myocardial injury
and fibrosis associated with MI is through CMR-based assessments of
LGE.
 LGE has several important uses in the setting of patients with
suspected CAD. These include:
A. Identification of the extent of acute and remote MI
B. Prediction of recovery of myocardial contractility after successful coronary artery
revascularization in chronic ischemic heart disease
C. Characterization of prognosis, visualization of cardiac thrombus or microvascular
obstruction
D. and, when combined with T2 imaging methods, localization of the area of
myocardial salvage

 High correlations between LGE and TTC-stained measures of infarcted
myocardial segments.
 The relatively high spatial resolution of LGE images enhances its sensitivity for
detecting MI.
 CMR may be used to identify micro infarcts because of relatively small
epicardial coronary artery branch occlusions or embolization of distal vessels
related to percutaneous coronary artery revascularization procedures.
 CMR has been shown to be more sensitive than both SPECT and PET imaging
for detecting small infarcts.
 In a large multicenter clinical trial of 282 patients, the sensitivity for detecting
acute MI was 99%.

 Transmural extent of LGE can additionally predict the likelihood of
functional recovery of stunned myocardium because there is an inverse
relationship between transmurality and recovery of function.
 In patients evaluated chronically (months to years) after MI, the
assessment of transmural extent of infarction has also been shown to
identify the likelihood of functional recovery of systolic thickening after
percutaneous coronary artery revascularization procedures.

 For those individuals with no LGE, recovery of function of resting segments
with akinesis can approach 80%. Conversely, in those individuals with greater
than 50% transmural extent of infarction, the likelihood of recovery of systolic
thickening after coronary artery revascularization falls below 10%.
 When the transmural extent of infarction ranges between 1% and 50%. In these
situations, there is approximately a 40% to 60% chance of recovery of systolic
thickening.
 The ability to identify those segments with a potential for systolic thickening
after revascularization improves to nearly 90% through the identification of
contractile reserve with low dose intravenous dobutamine.

Microvascular Obstruction
 In the setting of acute MI, the coronary artery microcirculation can be damaged to an
extent such that no gadolinium may be temporarily delivered to specific areas within an
infarct zone. No Reflow Phenomenon.
 These areas have been shown histopathologically to be associated with microvascular
obstruction caused by plugging of the small arterioles with thrombotic debris.
 The characteristic image finding indicates a very dark central core nested within a
relatively bright LGE region of myocardium consistent with acute/subacute necrosis.
Often on the cine wall motion images, these areas display marked hypokinesis or
akinesis.
 Presence of microvascular obstruction is associated with an adverse cardiac prognosis
and very little opportunity for recovery of systolic thickening longitudinally over time. In
addition, the presence of microvascular obstruction has also been associated with adverse
LV remodeling and worse patient outcomes.

Myocardial Area at Risk and Salvageable
Myocardium
 Patients presenting with acute chest pain syndromes, it is important to
recognize that edema imaging utilizing either T2-weighted or T2 mapping
sequences may be combined with LGE techniques to identify the area at
risk and salvageable myocardium as well as to differentiate stress-induced
cardiomyopathies from actual MI.
 In the setting of an acute infarction, bright signal observed in T2 imaging
techniques predicts the maximal area of myocardium that is at risk for necrosis.
 Myocardial salvage relates to a term that defines the difference between the
area at risk subtracted from the extent of necrosis as determined with LGE.
This region represents an area of risk of reinfarction in patients in whom
inadequate coronary artery blood flow recurs.

Intramyocardial Hemorrhage
 CMR is well suited to identify intramyocardial hemorrhage utilizing a
combination of T2-weighted and T2*-weighted imaging, as well as LGE.
 T2*-weighted imaging is very useful to identify the presence of hemoglobin
degradation products. These products produce a low signal intensity on T2*-
weighted images.
 Hemorrhagic infarcts are associated with infarction transmurality, a larger MI
size, and reduced LVEF.
 Those with myocardial hemorrhage experienced a greater increase in LV end
systolic volume 4 months after the infarct relative to those without evidence of
myocardial hemorrhage. These data suggest that the presence of myocardial
hemorrhage identified by T2*-weighted imaging during CMR may predict
adverse LV remodeling.

Imaging of atherosclerotic plaques
 MRI of Carotid artery and Descending aorta remains the most comprehensive
non invasive method to assess plaque structure and activity
 Carotid bifurcation is relatively immobile, large, and superficial to the skin
surface, and it shows the full spectrum of atherosclerotic lesion types.
 Contrast weighted sequences helps to discriminate fibrous cap, hemorrhage,
calcifications, and loose matrix.
 Contrast enhanced dynamic MRI - plaque neovascularisation
 USPIO (Ultrasmall super-paramagnetic particles of iron oxide) target
macrophage activity at high affinity based on histologic and electron
microscopic analyses of atherosclerotic plaques and this may be imaged using
T2* Weighted MRI
 24 to 36 hours after USPIO injection carotid macrophage plaque activity can
be measured

Accurate assessment of Regional viability

 CMR is an extremely useful technique in the assessment of the heart
failure (HF) patient.
 The pattern of LGE can be quite useful in differentiating causes of
cardiomyopathies.
 T2-weighted imaging can be used to demonstrate myocardial edema,
such as in acute myocarditis.

 The utility of DE-MRI in the setting of cardiomyopathy is based on the
understanding that rather than simply measuring viability, the presence and
pattern of hyperenhancement holds additional information. Recently, a
systematic approach to interpreting DE-MRI images in patients with heart
failure or cardiomyopathy has been proposed.
 This approach is based on the following three steps.
 Step 1: The presence or absence of hyperenhancement is determined.
In the subset of patients with longstanding severe ischemic
cardiomyopathy, the data indicate that virtually all patients have prior MI.
The implication is that in patients with severe cardiomyopathy but without
hyperenhancement, the diagnosis of idiopathic dilated cardiomyopathy
should be strongly considered.

 Step 2: If hyperenhancement is present, the location and distribution of
hyperenhancement should be classified as a CAD or non-CAD pattern. To
distinguish these patterns, the concept that ischemic injury progresses as a
wavefront from the subendocardium to the epicardium is fundamental.For
example, hyperenhancement patterns that spare the subendocardium and are
limited to the middle or epicardial portion of the LV wall should generally be
considered as non-CAD.
 Step 3: If hyperenhancement is present in a non-CAD pattern, further
classification should be considered. There are now considerable data that
demonstrate that certain nonischemic cardiomyopathies have predilection for
specific scar patterns.

HCM
 Pathological and physiological LVH
 End-diastolic wall thickness–to–cavity volume ratio less than 0.15
mm/mL/m2 and lack of LGE of the ventricular myocardium can provide
accurate differentiation between physiologic and pathologic LVH.
 Myocardial scarring is common in HCM patients who are asymptomatic
or minimally symptomatic.
 Rickers et al reported that in 6% of patients with suspected or known HCM,
cineMRI established the diagnosis of HCM, whereas no hypertrophy was seen
on echocardiography.
 Echo underestimates hypertrophy in basal anterolateral wall by 33% as
compared to CMR. In addition 40% of Apical Aneurysm are missed by Echo.
 Can assess septal thickness after surgical myomectomy/Alcohol septal ablation.
 Markedly elevated LV mass index (men > 91 g/m2; women > 69 g/ m2)
sensitive (100%), maximal wall thickness of more than 30 mm specific (91%)
for cardiac deaths

Myocarditis
 CMR targets 3 main pathophysiological processes:
1. Myocardial edema by T2-weighted imaging,
2. Regional hyperemia and capillary leak by early gadolinium
enhancement ratio (EGEr),
3. and myocardial necrosis or fibrosis by LGE imaging.
 In cases with high index of clinical suspicion but negative CMR tissue
findings, a repeat study in a few weeks may be necessary for diagnosis
because inflammation may be focal and difficult to detect in the first
few days of disease.
 Early evidence has indicated that a persistence of LGE 4 weeks after
symptom onset is predictive of adverse functional and clinical
outcomes.

 Subepicardium and mid myocardium are usually
involved and Parvovirus has been implicated in these
cases.
 Septal involvement is associated with HHV 6 and has
more serious sequelae.

ARVD
 CMR had a sensitivity of 96% and a specificity of 78% in detecting
ARVC
 Quantitative and volumetric assessment of cardiac function
 Necropsy studies have demonstrated that intramyocardial fat is
frequently seen in normal hearts and that fat infiltration per se should
not be considered synonymous with ARVC.
 Assessment of RV function is more reproducible and specific than fat
infiltration.
 Hyperenhancement consistent with RV fibrosis is found in 67% who
met Task Force criteria for ARVC.
 There is an excellent correlation with histopathology, and DE-MRI
findings were strongly associated with inducible ventricular tachycardia
on programmed electrical stimulation.

Iron overload cardiomyopathies
 Hemolytic anemias/iron overload pathologies
 T2* mapping to exclude cardiac siderosis
 T2* CMR enables amount of myocardial iron to be
estimated
 T2* value < 20 ms highly suggestive of cardiac siderosis
 T2* < 10 ms prone for heart failure
 Used to assess response to chelation therapy

 CMR is helpful in planning EPS procedures given its ability to identify
potential site of ablation or scars and to provide 3D Vol. mapping of
the Atria and Ventricles.
 In patients with AF undergoing Pulmonary venous isolation LA
emptying function and evidence of LV fibrosis are strong markers of AF
recurrence.
 CMR contributes to assessment of patients at risk of SCD by
Quantitation of LVEF & RV pathology, detection of myocardial scar,
identification of Anomalous Coronaries.
 LGE size is a robust risk marker for SCD independent of LVEF.

Pericardial effusion
 Loculated and circumferential effusions
 Simple transudative effusions typically appear bright and homogenous
on T2-weighted images and dark on T1-weighted images. On SSFP
cineMRI, which exhibits T2/T1 weighing, simple effusions appear
bright with the same or even higher image intensity than epicardial fat.
 Complex effusions may appear heterogeneous and darker on T2 and
SSFP imaging. Additionally, unlike simple effusions, complex effusions
may demonstrate increased image intensity on T1weighted imaging
after administration of gadolinium contrast media.

 With T1-weighted FSE imaging, a thickness of up to 3 mm is accepted
as normal.
 First-pass perfusion and pre- and postcontrast T1-weighted techniques
also may be necessary to determine vascularity of a pericardial mass
(e.g., to differentiate tumor vs thrombus).
 CMR is the current test of choice for differentiating constrictive
pericarditis from restrictive cardiomyopathy, not only by assessing
pericardial thickness but also by detecting signs of constrictive
physiology.
 Computed tomography can demonstrate pericardial calcifications but
is inferior to CMR in its limited hemodynamic data and tissue
characterization.

 CMR can provide key additive data beyond other
imaging methods in assessment of congenital heart
disease based on :
 no need for ionizing radiation,
 3D tomographic imaging of thoracic structures, and
 correlation of complex anatomy with blood flow and physiology

 Compared with echocardiography, CMR is thus more sensitive in
detecting three-dimensional change in ventricular size, function, and
myocardial mass. For aortic stenosis, CMR can visualize and achieve
direct planimetry of the aortic valve orifice at high spatial resolution.
 CMR is a useful tool in assessing patients before or after TAVR.
 Compared to TTE, CMR is more accurate in sizing the Aortic Annulus
before the procedure, which predicts the severity of Aortic regurgitation
after TAVR.
 CMR is more sensitive in detecting significant paravalvular Aortic
regurgitation at TAVR.

 At present, a typical protocol for the evaluation of a cardiac mass
should consist of multiple pulse sequences where the aim is to assess
morphology, motion, perfusion, and delayed enhancement, in addition
to inherent differences in T1 and T2.
 Perfusion MRI may demonstrate increased vascularity, which may be
prominent in malignancies such as angiosarcoma;
 DE-MRI may identify areas of tissue necrosis within the core of a
malignant tumor, which appear as areas of hyperenhancement.
 Fat can be verified by imaging first without and then with fat saturation
techniques.

 Simple cysts can be identified by characteristic high image intensity on
SSFP sequences or by DE-MRI.
 Morphologic characteristics such as tissue invasion or compression,
flow obstruction, and associated pericardial effusion are imaged by this
protocol.

Thrombus
 LV thrombus most common in the LV apex.
 LGE imaging can detect thrombus with a higher sensitivity than
echocardiography by depicting high contrast between the dark
thrombus and its adjacent structures and by imaging in three
dimensions.
 Mural thrombus does not enhance on first-pass perfusion and often has
a characteristic etched appearance (black border surrounding a bright
center) on LGE imaging, thus providing higher diagnostic specificity
than anatomic information alone

 CMR showed higher sensitivity and specificity (88% and 99%,
respectively) than transthoracic (23% and 96%, respectively) and
transesophageal echocardiography (40% and 96%, respectively) for the
diagnosis of LV thrombus.
 patients with ischemic cardiomyopathy were more than five times more
likely to have thrombus than those with nonischemic cardiomyopathy
despite similar mean LVEF. Additionally, myocardial scarring, also
detected by DE-MRI, was identified as a novel risk factor for thrombus.
 Weinsaft et al showed that even when sonographic contrast is routinely
utilized, echocardiography may fail to identify up to 39% of thrombi
detected by DE-MRI.

Magnetic Resonance Spectroscopy
 MRS provides information regarding cellular metabolism.
 Free energy in ATP is produced and stored primarily in mitochondria
and carried to sites of energy consumption (e.g., myofibrils or ion
channels) as phosphocreatine (PCr) through diffusion.
 Phosphorus-31 MRS assesses energy metabolism and hence the
integrity of cellular function by quantifying the ratio of PCr and ATP.
 MRS currently is limited by the low signal-to-noise ratio owing to low
concentration of the high-energy phosphate molecules, resulting in a
limited sensitivity for detection of viable myocardium beyond the
anterior LV.

 However, proton (1H) MRS has up to 20-fold improved sensitivity over
that for 31P MRS and thus can quantify both phosphorylated and
unphosphorylated creatine in any part of the left ventricle.
 Using 1H MRS, lipid overstorage was observed in human myocytes in
diabetics in the absence of systolic dysfunction, which may have
implications for the development of diabetic cardiomyopathy.

Molecular CMR
 Molecular CMR imaging can theoretically provide dramatic
improvement in sensitivity and specificity of disease detection by
characterizing cellular process and also allow preclinical disease
detection.
 Use of gadolinium chelates combined with a fibrin-specific peptide
ligand has been demonstrated to detect thrombi in the left atrium and
coronary stents under experimental conditions.
 Other examples are the use of nanoparticles to target the adhesion
molecule ανβ3- integrin as a marker of angiogenesis in atherosclerosis,
and of USPIO particles to detect macrophages in inflamed carotid
plaques, and tracking of intramyocardial transplanted mesenchymal
stem cells in experimental infarction.

Cardiac MRI

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