PET v. SPECT Images

What’s the Difference?

The nuclear societies data support increased accuracy of PET over SPECT, particularly for heavier patients, where breast, chest wall, and diaphragmatic attenuation interfere with conventional SPECT. Patients who need PET because SPECT is not sufficient for their clinical presentations are individuals who: have suspected multi-vessel balanced or diffuse CAD, are morbidly obese (BMI > 40), cannot exercise, have dense breasts or breast implants, high-risk patients, or have previously had equivocal or inconclusive SPECT exams.

Limitations of SPECT include the obese population, which often produces low count studies resulting in poor diagnostic quality. Women’s breast tissues create “shadow artifacts” over the anterior wall and men’s diaphragms push up to mask inferior walls, both of which result in a limited SPECT. Even in a high quality nuclear cardiac lab there is the diagnostic dilemma: artifact versus true disease or disease that might be masked by artifact.

Cardiac PET holds advantages that go further than its ability to correct for attenuation artifacts, which has been a struggle for SPECT. PET has a high diagnostic accuracy regardless of patient status. There are high counting statistics in the myocardium with superior tracer extraction fractions and superior target to background. PET also possesses high-energy coincidence photons: 511 keV vs. 140 keV. Above all, PET maintains less radiation exposure for personnel.

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