6 Noninvasive Modalities

1

Positron Emission Tomography Myocardial Perfusion Imaging (PET MPI)

Like single-photon emission computed tomography (SPECT), PET is a functional imaging test that can be used for the diagnosis and risk stratification of CAD. It has a high diagnostic sensitivity and specificity, with high spatial resolution and attenuation correction. PET can also calculate coronary flow reserve, which is a powerful factor that can be used to estimate the risk of future cardiac events. PET can be used to measure the viability of myocardial tissue, helping to distinguish between scar and nearby tissue that is "stunned" but still viable.6

Despite its expanded applications, PET requires an onsite cyclotron or monthly generator replacement for the radiotracers used in imaging. The high cost of PET equipment may continue to limit its more widespread use. Furthermore, the short half-lives of PET radiotracers limit stress procedures to pharmacologic stress tests only.6

This test is considered an applicable imaging service under the Medicare Appropriate Use Criteria (AUC) program.9

Images courtesy of W. A. Jaber, MD
 

Focus on PET

  • It has high sensitivity and specificity for the diagnosis of CAD1,6
  • It can be used to detect perfusion defects6
  • Limited use with pharmacologic stress6
  • Able to quantify coronary blood flow6

2

Echocardiography (Echo)

Echo is a functional imaging test that can be used to evaluate the size of the heart and detect heart muscle weakness, heart valve problems, blood clots, and tumors.1,11 Echo perfusion images are taken using reflected ultrasound beams to visualize cardiac anatomic features in real time. Intravenous contrast agents may be used to enhance image quality.12

Comparing stress echo with resting echo results can help assess changes in ventricular function that may be caused by demand ischemia. The extent and severity of exercise-induced wall motion abnormalities are directly correlated with disease risk. A normal exercise echo result is associated with a very low risk of myocardial infarction (MI) or cardiovascular death.1

Image courtesy of H. C. Lewin, MD.
 

Focus on Echo12

  • It's a rapid test, providing immediate data on cardiac structure and function
  • It's relatively low cost and widely available
  • It doesn't use ionizing radiation

3

Cardiovascular Magnetic Resonance (CMR) Imaging

CMR imaging is used to assess the structure and function of the heart and primary blood vessels. It can also provide information on myocardial viability following MI, and on images of coronary arteries and atherosclerotic plaque. With pharmacologic stress, CMR imaging can be used to study wall motion abnormalities and left ventricular function. No radiation exposure is involved.13

Due to the generation of strong magnetic fields in CMR imaging, it isn't recommended in certain patients with cochlear implants, metal-containing ocular implants, pacing wires, pacemakers, or other implants that could be hazardous. Image acquisition can also be challenging in the context of arrhythmias and because of the need for extended breath holding.13

This test is considered an applicable imaging service under the Medicare AUC program.9

Images courtesy of D. H. Kwon, MD.
 

Focus on CMR Imaging13

  • It doesn't use iodine-containing dyes
  • It doesn't use ionizing radiation
  • It can be used with pharmacologic stress

4

Coronary Computed Tomography Angiography (CCTA)

Noninvasive multisection CCTA is an anatomic test that produces high-resolution images of the coronary anatomy to identify areas of obstructive CAD.1

False-positive results may occur when calcification of coronary artery plaques (part of the atherosclerotic process) interferes with accurate CCTA imaging of lesion severity. Patients who have extensive calcification or who are considered to be at high risk for CAD based on clinical assessment or previous test results may not be the most appropriate candidates for CCTA.1

This test is considered an applicable imaging service under the Medicare AUC program.9

Image courtesy of H. C. Lewin, MD.
 

Focus on CCTA1

  • It shows high-resolution images of the coronary anatomy
  • It has high negative predictive value for CAD
  • It can show stenotic lesions, arterial remodeling, and plaque

5

Coronary Artery Calcium (CAC) Scoring

CT scans can be used to measure calcium levels in coronary arteries, producing a CAC score. This score has been shown to have prognostic value in assessing CAD risk in asymptomatic patients and in predicting the presence of coronary stenosis in symptomatic patients. It can help rule out obstructive coronary disease in patients who have atypical chest pain and are considered to have a low risk of CAD based on clinical assessment.1

It is not clear how well the CAC score correlates to myocardial perfusion abnormalities. Some patients with a CAC score of zero may still have perfusion defects on nuclear MPI. Obstructive CAD may be present in younger patients despite low CAC scores because calcification of atherosclerotic plaques occurs later on in disease progression.1

Image courtesy of H. C. Lewin, MD.
 

Focus on CAC SCORING1

  • It measures calcium levels in coronary arteries
  • It has high sensitivity but low specificity for detecting CAD

6

Hybrid Imaging

Combination or "hybrid" cardiac imaging protocols use complementary data sets from anatomic and functional tests to provide comprehensive information about both anatomic and functional endpoints. For example, PET or SPECT combined with CT scanning allows for assessment of arterial remodeling and plaque composition in addition to assessing flow and severity of CAD. This information may improve diagnostic accuracy and assessment of patient risk to better inform treatment decisions.1

Despite the potential benefits, hybrid imaging may expose patients to additional radiation.1

This test is considered an applicable imaging service under the Medicare AUC program.9

Images courtesy of D. H. Kwon, MD.
 

Focus on Hybrid Imaging

  • It can provide both functional and anatomic information from a single imaging session6
  • It can provide complementary information to help make a better-informed decision1