Excerpt
Single-photon emission computed tomography (SPECT) has a pivotal role in the non-invasive evaluation of known or suspected coronary artery disease (CAD), thanks mainly to the myocardial perfusion imaging (MPI) assessment.
1 The use of electrocardiographic gating also enabled accurate measurements of left ventricle (LV) wall motion, ejection fractions, and volumes, which allows the possibility to integrate several important functional information to perfusion evaluation.
2 In the last years, the introduction of dedicated cardiac cameras equipped with Cadmium-Zinc-telluride (CZT) technology has further improved the spatial and temporal resolution, with a significant reduction in the acquisition time and injected dose.
3-
5 Nevertheless, attention should also be paid to unexpected artifacts using CZT detectors too. For example, a supine position could limit the evaluation of the inferior wall because of attenuation artifacts from diaphragmatic elevation or adjacent abdominal visceral activity, although less than expected with standard SPECT. Briefly, soft tissue attenuation of tracer activity can result in artifactual perfusion abnormalities in the right coronary artery and left circumflex territories. In such cases, it is advisable to add prone or upright imaging, because in the new position artifactual defects shall resolve or change their location, whereas true perfusion defects shall persist.
2 At present, there is more experience with the conventional supine/prone imaging,
4,
6,
7 while data about upright cardiac images are limited, particularly in female patients.
8,
9 Upright imaging has some benefits as compared with a prone acquisition because the former does not require the patient to raise both hands during image collection, so body posture is stable, and body movements are reduced. Also, prone imaging affects respiration: abdominal breathing prevails over chest breathing at rest, but the prone position places pressure on the abdomen and promotes chest breathing. Therefore, the upright position makes breathing easier with the patient in a relaxed state. At the same time, the movements of the diaphragm are broader in abdominal breathing than in chest breathing; thus, both imaging methods improve evaluation of the inferior wall for breathing-related artifacts. A 2-position imaging approach can be particularly helpful in female patients, in which breast attenuation artifact adds to the issues outlined above. Breast attenuation artifact is challenging when the left breast position varies between the rest-and-stress images. It can be confirmed by repeating the acquisition with the left breast repositioned or with prone or upright imaging to reduce breast attenuation artifacts.
2 There are few data in the literature on the direct comparison between prone and upright imaging. Nakaya et al. observed a higher rate of suppression of soft tissue attenuation artifacts with prone imaging compared to upright artifacts using a conventional gamma camera, but the difference did not affect visual evaluation.
10 Noteworthy, all the previously described artifacts were significantly more familiar with the traditional Anger cameras, which suffered from inaccurate LV reconstructions, above all in smaller hearts.
11 On the contrary, CZT cameras allow the physician to rely on a single position (i.e., supine) in most cases, both in male and female patients.
2,
4,
12 The higher reliability of CZT detectors also lies with the acquisition of a comprehensive dataset on LV function from gated SPECT that can be integrated with MPI into the final interpretation. Therefore, the physician can readily verify whenever fixed, non-reversible perfusion defects are associated with abnormalities in wall motion or myocardial systolic thickening; a mismatch is more likely to be an artifact, notably if the clinical data do not support a prior infarction. Finally, attenuation correction is also possible with an attached full-size computed tomography (CT), which is a useful method to improve the diagnostic accuracy of the inferior wall ischemia.
13 Unfortunately, CT attenuation correction is not widely used due to the significant cost increase of the hardware. The assessment of the potential additional value of upright imaging to the conventional supine imaging is useful to weigh the need for a longer acquisition and manage discordant findings between upright and supine images. In the current issue of the Journal of Nuclear Cardiology, Muhammad W. Athar and associates analyzed supine and upright images after stress and at rest using a D-SPECT CZT dedicated cardiac camera.
14 The authors found that MPI assessment by multiple nuclear test quantitative variables was more accurate in supine than upright imaging, both in male and female patients. These findings, if confirmed by more extensive studies, may limit the patient selection for upright CZT imaging system. …
