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  IN THIS Article
 ::  Abstract
 ::  Cardiac MRI
 ::  Cardiac CT
 ::  Conclusion
 ::  References
 ::  Article Figures

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SYMPOSIUM
Year : 2010  |  Volume : 56  |  Issue : 2  |  Page : 125-130

Cardiac imaging: Current and emerging applications


1 Piramal Diagnostic Services (Formerly Wellspring), Piramal Diagnostics - Jankharia Imaging, Bhaveshwar Vihar, India
2 Department of Radiology, KEM Hospital, Parel, Mumbai, India

Date of Submission13-Jan-2009
Date of Decision12-Mar-2009
Date of Acceptance20-Feb-2010
Date of Web Publication8-Jul-2010

Correspondence Address:
B Jankharia
Piramal Diagnostic Services (Formerly Wellspring), Piramal Diagnostics - Jankharia Imaging, Bhaveshwar Vihar
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0022-3859.65289

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 :: Abstract 

Cardiac magnetic resonance imaging (MRI) and computed tomography (CT) scan have made big inroads as modalities used for evaluation of various pathologies of the heart. Cardiac MRI is typically used for perfusion and viability studies as well as to study various cardiomyopathies, valvular diseases and the pericardium. It has been used in the evaluation of congenital heart diseases over the last two decades. Cardiac CT is used mainly for the evaluation of the coronary arteries, typically in the setting of "to rule out coronary artery disease".


Keywords: Cardiac computed tomography, cardiac magnetic resonance imaging, computed tomography, congenital heart disease, coronary artery disease, magnetic resonance imaging, review, viability


How to cite this article:
Jankharia B, Raut A. Cardiac imaging: Current and emerging applications. J Postgrad Med 2010;56:125-30

How to cite this URL:
Jankharia B, Raut A. Cardiac imaging: Current and emerging applications. J Postgrad Med [serial online] 2010 [cited 2019 Nov 16];56:125-30. Available from: http://www.jpgmonline.com/text.asp?2010/56/2/125/65289


Cardiac magnetic resonance imaging (CMR) and cardiac CT (CCT) are the new kids on the block as far as cardiac imaging is concerned. This review describes the indications for these two modalities.


 :: Cardiac MRI Top


Instrumentation

A 1.5T scanner is required with high-speed gradients and specialized scanning sequences.

Imaging sequences

Image acquisition is done in a particular phase of cardiac cycle to avoid image blur and cardiac motion artifacts. This is called as electrocardiographic gating.

Pulse sequences used for CMR can be broadly divided into dark-blood and bright-blood techniques. A motion picture loop throughout the various phases of cardiac cycle can be produced with gradient echo (GRE) and balanced steady-state sequences to get rapid cine imaging. Cine imaging is useful in the functional assessment of ventricles.

Indications

Congenital heart disease

CMR is useful in understanding complex anatomy in Congenital heart disease (CHD) and gives information not obtained by echocardiography. [1] It is especially useful in evaluating the functional significance in various types of CHDs, e.g. in evaluating right heart function in Ebtein's anomaly. [2] CMR not only detects intraventricular shunts such as atrial and ventricular septal defects, but can also calculate shunt size with phase-velocity mapping. [3] CMR plays an important role in evaluating complex surgical shunts and baffles and has a very important role to play in the postoperative evaluation of patients with tetralogy of Fallot. [4]

Valvular heart disease

CMR can demonstrate the presence and quantify the severity of valvular heart disease. [5] Using phase-velocity mapping as well as ventricular chamber volumes, aortic stenosis and regurgitation as well as mitral disease can be accurately evaluated. The valve areas can be accurately measured using planimetry. [6]

Cardiomyopathies

Arrhythmogenic right ventricular dysplasia (ARVD) [Figure 1] is characterized by fatty or fibrous infiltration of the right ventricle (RV) walls with thinning and pseudo-sacculations. [7] The presence of fat can be identified on T1W images. The cine images show thinning of the anterior and inferior walls, enlargement and dilatation of the RV, areas of dyskinesia or focal bulging, reduced ejection fraction and impaired ventricular filling during diastole. [8]

Hypertrophic cardiomyopathy

The diagnosis is usually made on echocardiography. CMR is better than echocardiography for diagnosing apical hypertrophic cardiomyopathy. [9] CMR also helps in assessing the functional sub-valvular narrowing in patients with hypertrophic obstructive cardiomyopathy. [10] The presence of abnormal areas of enhancement suggests necrosis and fibrosis and may indicate an adverse prognosis. [11]

Inflammatory and infiltrative cardiomyopathy

CMR is an excellent tool for diagnosing myocardial inflammation as in viral myocarditis [12] or sarcoidosis. [13] Abnormal areas of mid-myocardial and epicardial enhancement are seen often with wall motion abnormality. Infiltrative conditions like Fabry's disease [14] and amyloidosis [15] can also be diagnosed reliably.

Iron deposition

In patients with thalassemia, iron deposition in the myocardium is a significant cause of death. [16] Using the T2* parameter, the myocardial iron content can be quantified and then followed up regularly to see efficacy of chelating agents. [17]

Ventricular function

CMR is more accurate than 2D echocardiography in the functional assessment of the heart. [18] CMR can measure ventricular ejection fraction and end-diastolic and end-systolic volumes.

Coronary artery imaging

Despite reports in the literature, [19],[20] CMR is still not a robust modality for the evaluation of the coronary arteries. [21]

Myocardial perfusion and viability

Perfusion: First pass perfusion studies can be performed using intravenous gadolinium and stress with either adenosine or dipyridamole. [22] The technique is sensitive for diagnosing areas of hypoperfusion, corresponding to the presence of ischemia. [23]

Myocardial viability [Figure 2]

Using special sequences, delayed hyperenhancement can be studied with CMR. It has been shown that all infarcts [24] show delayed hyperenhancement, 5-10 min after the injection of intravenous gadolinium. The extent of infarction correlates with the ability to recover function after revascularization [25] and thus this study can help decide whether revascularization will be of help in patients with myocardial infarction.

Cardiac and pericardial masses and thrombi

CMR is an accurate means to evaluate cardiac and pericardial masses. [26] Gadolinium enhancement differentiates thrombus from neoplasm. [27]

Pericardial diseases

CMR is an accurate tool for diagnosing pericardial effusion and constrictive pericarditis. [28] Pericardial thickening of more than 4 mm in a patient with a restrictive physiology is usually diagnostic. [29] The presence of paradoxical septal deviation in early diastole in the first expiratory breath on real-time CMR has been shown to be a useful sign to diagnose constriction. [30]


 :: Cardiac CT Top


Instrumentation

At the bare minimum, a 64-slice CT scanner is required for accurate CT angiography (CTA). [31] Faster, 256- and 320-slice [32] and dual-source [33] CT scanners are now available as well.

Procedure

Irrespective of the speed of the scanner, the best images are obtained with a lower heart rate [34] and thus beta-blockers are routinely used to bring down the heart rate to around 65 beats per min or less. Intravenous contrast is used at a high injection speed to opacity the coronary arteries. A calcium score study is often performed prior to the intravenous injection and in some centers if the score is more than 800, a CTA is then not performed. Cardiac CT is contraindicated in those patients with severe allergy to iodinated contrast or in those suspected to be pregnant.

Indications

Coronary artery imaging

Cardiac CT has a negative predictive value of around 97-99% [35],[36] in the evaluation of coronary artery disease [Figure 3]. The positive predictive value varies from 44-93%, depending on the patient selection criteria. [37] In view of this, the main indication of cardiac CT is still in the setting of "to rule out coronary artery disease", i.e. to screen for coronary artery pathology in the setting of medium to high-risk but asymptomatic patients or in patients with atypical symptoms. [36]

Post-bypass [Figure 4]

Cardiac CT is an excellent tool to study bypass grafts and to assess their patency [38] and is currently used as the first tool in the evaluation of patients suspected to have graft pathology.

Post-stent

The results in patients with stents to diagnose in-stent pathology are quite variable [39] due to difficulties in in-stent lumen visualization, and cardiac CT is typically used mainly in patients with larger stents and to look at disease elsewhere in the coronary tree. Catheter angiography remains the gold standard for in-stent lumen visualization.

Coronary artery anomalies

Cardiac CT is the gold standard in the evaluation of coronary artery anomalies. [40]

Functional assessment

Cardiac CT reconstruction in multiple phases allows the assessment of ejection fraction and end-diastolic and end-systolic volumes with considerable accuracy. [41]

Valvular diseases

Cardiac CT has been found useful in the evaluation of aortic and mitral valve areas and the extent of calcification. [42] The evaluation of valve areas may help in decision-making as far as management is concerned.

Pericardium and cardiac and pericardial masses

Cardiac CT is useful in diagnosing pericardial thickening, calcification, effusion and masses [43] as well as cardiac masses. [44]

Congenital heart disease

The role of cardiac CT in CHD is mainly to evaluate the pulmonary arteries, veins and aorta. [45] It is especially useful in patients with pulmonary atresia to evaluate the presence and extent of major aorto-pulmonary collaterals [46] [Figure 5]. It also helps in the evaluation of Glenn and Fontan shunts [47] and in other postoperative situations.


 :: Conclusion Top


Both cardiac CT and CMR have become extremely useful tools to study various facets of the heart as described above. They both have different strengths. Cardiac CT is best suited to study the coronary tree. CMR is best used to evaluate the myocardium, pericardium and the valves.

 
 :: References Top

1.Gutierrez FR, Ho ML, Siegel MJ. Practical applications of magnetic resonance in congenital heart disease. Magn Reson Imaging Clin N Am 2008;16:403-35.  Back to cited text no. 1      
2.Cantinotti M, Bell A, Razavi R. Role of magnetic resonance imaging in different ways of presentation of Ebstein's anomaly. J Cardiovasc Med (Hagerstown) 2008;9:628-30.  Back to cited text no. 2      
3.Piaw CS, Kiam OT, Rapaee A, Khoon LC, Bang LH, Ling CW, et al. Use of non-invasive phase contrast magnetic resonance imaging for estimation of atrial septal defect size and morphology: A comparison with transesophageal echo. Cardiovasc Intervent Radiol 2006;29:230-4.  Back to cited text no. 3      
4.Norton KI, Tong C, Glass RB, Nielsen JC. Cardiac MR imaging assessment following tetralogy of fallot repair. Radiographics 2006;26:197-211.  Back to cited text no. 4      
5.Masci PG, Dymarkowski S, Bogaert J. Valvular heart disease: What does cardiovascular MRI add? Eur Radiol 2008;18:197-208.  Back to cited text no. 5      
6.Pouleur AC, le Polain de Waroux JB, Pasquet A, Vancraeynest D, Vanoverschelde JL, Gerber BL. Planimetric and continuity equation assessment of aortic valve area: Head to head comparison between cardiac magnetic resonance and echocardiography. J Magn Reson Imaging 2007;26:1436-43.  Back to cited text no. 6      
7.Boxt LM, Rozenshtein A. MR imaging of arrhythmogenic right ventricular dysplasia. Magn Reson Imaging Clin N Am 2003;11:163-71.  Back to cited text no. 7      
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24.Kim RJ, Wu E, Rafael A, Chen EL, Parker MA, Simonetti O, et al. The use of contrast-enhanced magnetic resonance imaging to identify reversible myocardial dysfunction. N Engl J Med 2000;343:1445-53.  Back to cited text no. 24      
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31.Pugliese F, Mollet NR, Runza G, van Mieghem C, Meijboom WB, Malagutti P, et al. Diagnostic accuracy of non-invasive 64-slice CT coronary angiography in patients with stable angina pectoris. Eur Radiol 2006;16:575-82.  Back to cited text no. 31      
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45.Lee T, Tsai IC, Fu YC, Jan SL, Wang CC, Chang Y, et al. Using multidetector-row CT in neonates with complex congenital heart disease to replace diagnostic cardiac catheterization for anatomical investigation: Initial experiences in technical and clinical feasibility. Pediatr Radiol 2006;36:1273-82.  Back to cited text no. 45      
46.Hayabuchi Y, Inoue M, Watanabe N, Sakata M, Nabo MM, Kitagawa T, et al. Assessment of systemic-pulmonary collateral arteries in children with cyanotic congenital heart disease using multidetector-row computed tomography: Comparison with conventional angiography. Int J Cardiol 2010;138:266-71.  Back to cited text no. 46      
47.Leschka S, Oechslin E, Husmann L, Desbiolles L, Marincek B, Genoni M, et al. Pre- and postoperative evaluation of congenital heart disease in children and adults with 64-section CT. Radiographics 2007;27:829-46.  Back to cited text no. 47      


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]

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