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.


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