Positron Emission Tomography (PET) in Cardiology

Positron Emission Tomography (PET) in Cardiology

Positron emission tomography (PET) imaging is useful in assessment of myocardial perfusion and viability, atherosclerotic plaque activity as well as cardiac innervation in heart failure. PET is also useful in prosthetic valve endocarditis, endocarditis associated with cardiac implantable electronic devices (CIED), infiltrative cardiomyopathy, aortic stenosis and cardio oncology [1].

PET imaging has superior diagnostic accuracy compared to SPECT (Single Photon Emission Computed Tomography). It has improved spatial and temporal resolution and can measure regional blood flow and has less radiation. In PET, high energy gamma rays of 511 KEV (Kilo Electron Volts) are emitted at 180 degrees during annihilation of the positron and electron. This compares with 140 KEV for technetium. The high energy gamma rays are absorbed by the detectors, giving better resolution images. The radiation exposure of PET was reported as 6 mSv versus 11.6  mSv for SPECT [2].

A meta-analysis compared 82Rb PET with SPECT regarding the detection of obstructive CAD [3]. 15 studies on PET and 8 studies on SPECT having 1344 and 1755 patients respectively were included. They concluded that 82Rb PET is accurate for the detection of obstructive coronary artery disease and is superior to SPECT.

The extent and severity of ischemia and scar noted on PET stress myocardial perfusion imaging has been shown to be a powerful and incremental risk predictor for cardiac death and all cause mortality compared to traditional coronary risk factors [4]. Thus PET is useful in risk stratification as well.

Another role of PET is in the identification of hibernating myocardium which will benefit from revascularization. Preserved metabolic activity in the myocardium noted on PET has been considered the gold standard for myocardial viability. 61 patients with regional wall motion abnormality underwent PET before revascularization. 43 patients who had successful revascularization were included in a study. Patients underwent rest-stress 13N ammonia perfusion scans and FDG scans at rest in a fasting state. FDG PET had best predictive value for improvement in wall motion after revascularization. 13N ammonia PET was useful in predicting non-reversible myocardial scarring when it shows severe hypoperfusion at rest or hypoperfusion without stress induced ischemia [5].

In prosthetic valve endocarditis, acoustic shadowing by the prosthetic valve makes detection of small vegetations in endocarditis difficult. In a study of 72 patients with suspected prosthetic valve endocarditis, 36 had abnormal 18F-fluorodeoxyglucose (18FDG) uptake around the site of the prosthetic valve. This increased the sensitivity of modified Duke criteria at admission from 70% to 97%. FDG is able to identify inflammatory and infectious processes by measuring the metabolic tissue activity. Authors suggested adding FDG uptake around the prosthetic valve as major criterion for the diagnosis of prosthetic valve endocarditis [6].

Similar role for PET has been established in CIED associated infections [7]. In a study, 32 of the 42 patients with suspected CIED infection had positive PET/CT. 24 of them underwent extraction with excellent correlation. 6 patients were treated as superficial infection and had clinical resolution. In one patient, positive PET/CT with negative leucocyte scan was considered as false positive due to Dacron pouch. Remaining 10 patients with negative PET/CT were treated with antibiotics and none had relapse over a mean follow period of 12.9 months.

PET is also useful in the evaluation of cardiac sarcoidosis. In a study, 118 patients were evaluated with 18FDG PET to assess inflammation and 82Rb PET to assess perfusion defects following a high fat/low carbohydrate diet to suppress normal myocardial glucose uptake [8]. The presence of focal perfusion defect and FDG uptake on PET identified patients at higher risk of death or ventricular tachycardia in the study.

Pittsburgh B Compound PET (¹¹C-PiB PET) in patients with light chain (AL) cardiac amyloidosis has shown that 11C-PiB PET indicates the degree of amyloid deposit and is an independent predictor of clinical outcome [9]. 18F sodium fluoride PET may be useful for disease monitoring and localizing amyloid deposition in transthyretin amyloidosis [10].

18FDG PET and computed tomography (CT) can measure disease activity and progression in aortic stenosis [11]. PET can measure valvular calcification and inflammation in aortic stenosis [12]. These are assessed using 18F sodium fluoride and 18FDG PET. Correlation with disease severity was strongest for 18F sodium fluoride PET.

PET has application in cardio oncology as well. Presence of uptake in the right ventricular wall in PET/CT after therapy with anthracycline or trastuzumab in breast cancer patients were associated with cardiotoxicity [13]. Thus oncologic FDG PET/CT scans provide information on tumour response and therapy induced cardiotoxicity.

References

1. Tarkin JM, Ćorović A, Wall C, Gopalan D, Rudd JH. Positron emission tomography imaging in cardiovascular disease. Heart. 2020 Nov;106(22):1712-1718.
2. Hlatky MA, Shilane D, Hachamovitch R, Dicarli MF; SPARC Investigators. Economic outcomes in the Study of Myocardial Perfusion and Coronary Anatomy Imaging Roles in Coronary Artery Disease registry: the SPARC Study. J Am Coll Cardiol. 2014 Mar 18;63(10):1002-8.
3. Mc Ardle BA, Dowsley TF, deKemp RA, Wells GA, Beanlands RS. Does rubidium-82 PET have superior accuracy to SPECT perfusion imaging for the diagnosis of obstructive coronary disease?: A systematic review and meta-analysis. J Am Coll Cardiol. 2012 Oct 30;60(18):1828-37. 
4. Dorbala S, Di Carli MF, Beanlands RS, Merhige ME, Williams BA, Veledar E, Chow BJ, Min JK, Pencina MJ, Berman DS, Shaw LJ. Prognostic value of stress myocardial perfusion positron emission tomography: results from a multicenter observational registry. J Am Coll Cardiol. 2013 Jan 15;61(2):176-84. 
5. Tamaki N, Kawamoto M, Tadamura E, Magata Y, Yonekura Y, Nohara R, Sasayama S, Nishimura K, Ban T, Konishi J. Prediction of reversible ischemia after revascularization. Perfusion and metabolic studies with positron emission tomography. Circulation. 1995 Mar 15;91(6):1697-705.
6. Saby L, Laas O, Habib G, Cammilleri S, Mancini J, Tessonnier L, Casalta JP, Gouriet F, Riberi A, Avierinos JF, Collart F, Mundler O, Raoult D, Thuny F. Positron emission tomography/computed tomography for diagnosis of prosthetic valve endocarditis: increased valvular 18F-fluorodeoxyglucose uptake as a novel major criterion. J Am Coll Cardiol. 2013 Jun 11;61(23):2374-82.
7. Sarrazin JF, Philippon F, Tessier M, Guimond J, Molin F, Champagne J, Nault I, Blier L, Nadeau M, Charbonneau L, Trottier M, O’Hara G. Usefulness of fluorine-18 positron emission tomography/computed tomography for identification of cardiovascular implantable electronic device infections. J Am Coll Cardiol. 2012 May 1;59(18):1616-25. 
8. Blankstein R, Osborne M, Naya M, Waller A, Kim CK, Murthy VL, Kazemian P, Kwong RY, Tokuda M, Skali H, Padera R, Hainer J, Stevenson WG, Dorbala S, Di Carli MF. Cardiac positron emission tomography enhances prognostic assessments of patients with suspected cardiac sarcoidosis. J Am Coll Cardiol. 2014 Feb 4;63(4):329-36. 
9. Lee SP, Suh HY, Park S, Oh S, Kwak SG, Kim HM, Koh Y, Park JB, Kim HK, Cho HJ, Kim YJ, Kim I, Yoon SS, Seo JW, Paeng JC, Sohn DW. Pittsburgh B Compound Positron Emission Tomography in Patients With AL Cardiac Amyloidosis. J Am Coll Cardiol. 2020 Feb 4;75(4):380-390.
10. Morgenstern R, Yeh R, Castano A, Maurer MS, Bokhari S. ¹⁸Fluorine sodium fluoride positron emission tomography, a potential biomarker of transthyretin cardiac amyloidosis. J Nucl Cardiol. 2018 Oct;25(5):1559-1567. 
11. Pawade TA, Cartlidge TR, Jenkins WS, Adamson PD, Robson P, Lucatelli C, Van Beek EJ, Prendergast B, Denison AR, Forsyth L, Rudd JH, Fayad ZA, Fletcher A, Tuck S, Newby DE, Dweck MR. Optimization and Reproducibility of Aortic Valve 18F-Fluoride Positron Emission Tomography in Patients With Aortic Stenosis. Circ Cardiovasc Imaging. 2016 Oct;9(10):e005131. 
12. Dweck MR, Jones C, Joshi NV, Fletcher AM, Richardson H, White A, Marsden M, Pessotto R, Clark JC, Wallace WA, Salter DM, McKillop G, van Beek EJ, Boon NA, Rudd JH, Newby DE. Assessment of valvular calcification and inflammation by positron emission tomography in patients with aortic stenosis. Circulation. 2012 Jan 3;125(1):76-86. 
13. Kim J, Cho SG, Kang SR, Yoo SW, Kwon SY, Min JJ, Bom HS, Song HC. Association between FDG uptake in the right ventricular myocardium and cancer therapy-induced cardiotoxicity. J Nucl Cardiol. 2020 Dec;27(6):2154-2163.