Interpreting myocardial perfusion scintigraphy using single-photon emission computed tomography. Part 1

Abstract

This article discusses the protocol for myocardial perfusion scintigraphy performed with single-photon emission computed tomography (SPECT). Indications for SPECT are listed with consideration given to the results of the increasingly more common angio-CT examinations of the coronary arteries (multislice computed tomography). The paper also presents basic information about interpreting the results, including the scores of left ventricle myocardial perfusion using the 17-segment polar map, and explains the concept of total perfusion deficit.

Keywords: bool eye imaging; coronary artery disease; myocardial perfusion scintigraphy.

Fig. 1

Protocols for two-day (top) and one-day (bottom) examinations. The radiopharmaceutical labeled with ^99mTc accumulates in cardiomyocytes proportionally to the flow of blood and is not subject to redistribution. The accumulation of the radiotracer reflects the flow of blood (myocardial perfusion) at the time when the radiotracer is intravenously injected. In order to obtain the image of cardiac perfusion during stress and rest, the radiotracer must be administered twice: at the peak of stress and during rest. In patients with a low risk of coronary artery disease, the initial examination should consist in stress scintigraphy. The two-day protocol is recommended in patients after coronary incidents or after percutaneous or surgical revascularization; in this case, the order in which the examinations are performed has little significance as the image has to be registered both under conditions of stress (exercise or pharmacological provocation with dobutamine or adenosine) and during rest. If the one-day protocol is employed, the first examination is usually the stress examination, with radiotracer dosage of approximately 8–10 mCi. After 3 h, a resting examination is performed with a higher dose of the isotope (24–30 mCi). Both the one-day and the two-day protocol can be considered to have equal diagnostic value; the choice which one to use depends on the preferences of the laboratory performing the investigation

Fig. 2

The principles of constructing a polar map

Fig. 3

Normal results of myocardial perfusion scintigraphy. Middle: a normal polar map of left ventricular perfusion with noticeably lower radiotracer activity on the circumference of the basal segments and, to a lesser degree, in the apex. Top right: stress and rest perfusion scores (in this case amounting to 0 points). Bottom right: the polar map divided into 17 segments. The examination was performed in the Laboratory of Nuclear Medicine of the Silesian Center for Heart Diseases in Zabrze (Cedars-Sinai Medical Center software; QPS – Quantified Perfusion Spect)

Fig. 4

Polar map division according to Cedars-Sinai Medical Center software. Top left: polar map division based on arteries; top right: division based on coronary artery groups. In the polar map divided according to arteries, the areas which cannot be unequivocally assigned to the supply area of a particular coronary vessel due to variable vascularization are blackened. LAD – left anterior descending branch, Cx – circumflex branch, RCA – right coronary artery. Bottom: left ventricular polar map division into 17 segments according to the American Heart Association. The order in which the segments are numbered is counterclockwise. Basal segments are numbered 1–6, midle segments: 7–12, and paraapical segments: 13–16. The figure also assigns the segments to particular coronary artery groups. The area assigned to the left anterior descending artery and its branches is marked with blue; the group of segments assigned to the circumflex artery and its branches is marked with yellow, and the right coronary artery group is marked with red. It should be noted that the assignment of the polar map segments to specific coronary arteries is approximate and schematic; it may vary depending on the type of left ventricular vascularization

Fig. 5

The figure presents the extent of a stress perfusion deficit. All the areas on the polar map with values below normal are blackened (blackout polar map). The perfusion deficit involves the inferolateral wall, extending over 18 cm², i.e., 22% of the left ventricular surface. The ischemic area may correspond to the right coronary artery or the circumflex branch. The examination was performed in the Laboratory of Nuclear Medicine of the Silesian Center for Heart Diseases in Zabrze (Cedars-Sinai Medical Center software; QPS – Quantified Perfusion Spect)

Fig. 6

The figure presents the severity of a stress perfusion deficit (in the same patient as in Fig. 5). The most severe perfusion deficit is present in segment 5 (the inferolateral basal segment according to AHA), and the artery responsible for the ischemia is most likely the right coronary artery. The examination was performed in the Laboratory of Nuclear Medicine of the Silesian Center for Heart Diseases in Zabrze (QPS software)

Fig. 7

An example of scoring myocardial perfusion. In this case, the summed score of perfusion deficits amounted to 12 during stress (SSS) and 0 during rest (SRS). Therefore, the difference (SDS) amounted to 12 points. The perfusion deficit is located within the anterior wall, septum, and apex (supply area of the left anterior descending branch). Due to the number of segments affected by stress perfusion deficits, the examination result is significantly positive

Fig. 8

Illustration of the concept of Total Perfusion Deficit for a single cardiac segment. The light blue curve shows the circular activity profile, the dark blue curve shows the lower margin of the normal values of the activity profile