Case of the Month Jenny Delfin MD and Ola Akinboboye MD MPH MBA FACC.
Case Presentation • The patient is a 51 year old male with a history of hypertension, DM (II), and hyperlipidemia who presented to our institution with the chief complaint of non-exertional chest pain. • A 2 day stress-rest Tc-99m-sestamibi perfusion study was performed because of his size. • Exercise stress testing was performed on a treadmill using the Bruce protocol.
Case Presentation • Approximately 40 mCi of Tc-99m sestamibi was injected at rest and during stress. • Gated perfusion imaging was performed with attenuation correction using vantage software.
Case Presentation The patient was able to perform 7 minutes of Bruce protocol. Exercise was interrupted because of breathlessness, generalized and leg fatigue. The patient had no chest discomfort during exercise and recovery.
Case Presentation • The maximum heart rate and blood pressure during exercise were 171 bpm (101% of the predicted maximum heart rate for age) and 194/70 mmHg respectively. • The maximum workload attained was 9 METS. Cardiac exam was normal before and after exercise.
Case Presentation • The resting electrocardiogram revealed ST-T abnormalities. There was no electrocardiographic evidence of ischemia during exercise. • The SPECT myocardial perfusion scan raw data showed good image quality with a normal sized left ventricle. • Gated analysis did not reveal any significant wall motion abnormality.
Perfusion Scans • There was no significant perfusion abnormality on the uncorrected perfusion scans (fig 1). • The corrected scans showed a medium-size reversible basal-anterior perfusion abnormality with moderate reduction in counts (fig 2). • However, the quality control indices (fig 3) for the stress and rest studies showed critically low counts and the presence of truncation that was deemed to be non-critical.
Case Presentation • Because the patient has multiple risk factors including diabetes and an equivocal perfusion study, the referring physician elected to perform coronary angiography, which did not reveal any evidence of luminal coronary artery disease.
Teaching Point • The role of single photon emission computed tomography (SPECT) myocardial perfusion imaging in diagnosing and risk stratifying patients with known or suspected coronary artery disease (CAD) has been well established over the years. The sensitivity and specificity of SPECT MPI in detecting angiographically significant CAD are 88% (range 73-98%) and 77% (range 53-96%), respectively.
Teaching Point • One of the major limitations of SPECT MPI is attenuation artifact. More recently, commercialized SPECT attenuation correction systems have been used to overcome this major limitation . • External collimated radionuclide sources or x-ray CT with hybrid systems are utilized in SPECT attenuation correction systems to measure the non-homogeneous attenuation distribution. The attenuation map produced using these commercialized attenuation correction systems is essential for accurate attenuation correction.
Teaching Point • Quality control indices used for SPECT attenuation correction include count statistics, presence or absence of truncation, and presence or absence of banding. High quality attenuation maps should have high count density, minimal or no truncation, and minimal or no banding. Only studies with high quality attenuation maps should be used in assessing for attenuation artifact. . • Manufacturers of SPECT attenuation correction programs recommend that quality control indices be checked for every patient.
Teaching Point • Despite this recommendation, many physicians who interpret attenuation corrected images often forego this very important step, thus leading to incorrect interpretation of these images. • The presence of truncation, though non-critical and low count statistics on the transmission scan probably caused the false-positive perfusion abnormality on the attenuation corrected scans.
Teaching point • It is incumbent upon the physician reading attenuation corrected perfusion scans to confirm that quality control indices are of high quality prior to interpretation of the images.
References •  Lee TH, Boucher CA. Noninvasive tests in patients with stable coronary artery disease. NEJM 2001; 344: 1840-45. •  Bateman TM, Cullom SJ. Attenuation correction single-photon emission computed tomography myocardial perfusion imaging. Semin Nucl med 2005; 35:37-51. • 3)Attenuation correction of myocardial perfusion SPECT scintigraphy: A joint position statement by the American society of nuclear cardiology and the society of nuclear medicine. June 2003.