CARDIOVASCULAR JOURNAL OF AFRICA • Volume 25, No 4, July/August 2014
188
AFRICA
•
LGE sequences for detection of myocardial necrosis/fibrosis
•
T2-weighted images for assessment of myocardial oedema
44
•
T1-weighted sequences before and after contrast injection for
the detection of myocardial hyperaemia.
The Lake Louise criteria for CMR diagnosis of myocarditis state
that CMR findings are consistent with myocarditis if two out of
three of the above criteria are found to be positive.
45
Although
the CMR findings in myocarditis are not specific, they can act as
a useful tool for the assessment of myocardial inflammation in
patients with suspected acute myocarditis.
46
Pericardial disease
CMR is emerging as a most useful tool in the assessment of
the pericardium. CMR, owing to its excellent resolution, can
comprehensively assess pericardial anatomy. Through evaluation
of regional myocardial deformation, ventricular interaction
and venous return, CMR can also assess the physiological
consequences of pericardial constriction. Owing to its combined
anatomical and functional capabilities, CMR is a unique tool that
enables one to distinguish between restrictive cardiomyopathy
and constrictive pericarditis.
Congenital heart disease
Echocardiography is the primary diagnostic tool for the
assessment of congenital heart disease but CMR can provide
valuable information to confirm uncertain diagnoses. The large
field of view allows assessment of the anatomical relationships
between cardiac and vascular structures.
Valvular heart disease
Although echocardiography remains the initial tool for assessing
cardiac valves, CMR can provide similar information in
patients with sub-optimal or unsatisfactory echocardiographic
examination.
47
Valve anatomy and motion as well as the presence
of vegetations, thrombi or tumours can be visualised. Velocity
measurements canbe performed andpressure gradients calculated
accurately with good reproducibility. The concomitant excellent
determination of ventricular function and volume makes CMR
a good alternative when echocardiography is sub-optimal.
Cardiac masses
The goal of CMR for assessing cardiac and paracardiac masses
includes confirming or excluding a mass suspected by X-ray
or echocardiography, assessing its location, mobility and
relationship to surrounding tissues, and imaging the degree
of vascularity; and distinguishing solid lesions from fluid and
determining tissue characteristics as well as the specific nature of
a mass. Owing to its excellent resolution, tissue characterisation
andmultiplanar approach, the extent of intra- or pericardial mass
lesions can be clearly visualised. The additional administration
of gadolinium contrast agents can assess vascularity and help to
differentiate tumour from thrombus.
Coronary artery imaging with CMR
There has been continuous improvement in image quality
and examination time in coronary artery imaging with CMR.
Hamden
et al
.
48
recently compared 3.0-T MRI with 64-slice
CT angiography of the coronary arteries and concluded that,
although both modalities could similarly identify significant
coronary stenosis in patients with suspected or known CAD, CT
angiography showed a favourable trend towards higher diagnostic
performance. CMR is a most useful alternative modality to CT
for the detection of anomalous coronary vessels, especially when
ionised contrast administration is contra-indicated.
49
The future
Imaging speed is likely to continue to increase and larger and
larger imaging volumes will become accessible at any given
spatial and temporal resolution. The ability to accurately assess
total scar burden via T1 mapping could provide a more objective
method of non-invasively quantifying diffuse myocardial
fibrosis, as recent studies have validated this method in various
myocardial diseases.
50,51
Quantitative analysis of perfusion studies will become easier
and more applicable in the clinical setting. Myocardial tagging,
enabling the CMR specialist to quantify diastolic wall motion will
probablymovefromtheresearchenvironmentintoclinicalpractice.
Although coronary artery imaging via CMR is still in its infancy,
the imaging of carotid plaque composition looks promising,
especially in evaluating the response to lipid-lowering drugs.
52
Plaque characterisation with 3.0-T MRCA will probably play an
important role in the diagnosis and risk stratification of CAD
in the future.
Conclusion
CMR is a unique, versatile, rapidly evolving, non-invasive
diagnostic tool offering complete coverage of the heart, and
is independent of chest wall anatomy. Owing to its excellent
resolution, interstudy reproducibility, user independence and
absence of radiation exposure, it is bound to play an increasingly
important role in cardiac imaging.
CMR is regarded as the gold standard for evaluating
ventricular function, because of its reproducibility and validated
assessment of ventricular size, function and mass of both the
left and right ventricles. CMR plays an increasingly important
role in the work-up of ischaemic heart disease as well as the
non-ischaemic cardiomyopathies. Owing to the versatility and
multitude of possible sequences, it is necessary to assemble
lists of sequences into protocols that are specifically tailored to
diagnostic questions or scenarios, in order to decrease scan time,
and streamline and simplify the technique.
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