Comparison of 1‐ and 2‐day protocols for myocardial SPECT: a Monte Carlo study

Abstract

Myocardial perfusion single-photon emission tomography (SPET) is carried out by combining a rest and a stress study that are performed either on one day or two separate days. A problem when performing the two studies on one day is that the residual activity from the first study contributes to the activity measured in the second study. Our aim was to evaluate how the quantification of myocardial perfusion images is influenced by different types of one-and two-day rest-stress protocols.Methods: A digital phantom was used for the generation of heart images and a Monte Carlo based scintillation camera program was used to simulate SPET projection images. In our simulations, the rest images were normal and the stress images included lesions of different type and localisation. Two programs for quantification of myocardial perfusion images were used to assess the different images in an automated and objective way. Results:The summed difference scores observed with the two-day protocol were 3 ± 1 (mean ± SD) higher for AutoQUANT and 2 ± 1 higher for 4D-MSPECT compared to those observed with the one-day protocol. The extent values were 2 percentage points higher for the two-day protocol compared to the one-day protocol for both programs.Conclusions: There are differences in the quantitative assessment of perfusion defects depending on the type of protocol used. The contribution of residual activity is larger when a one-day protocol is used and if a high dose is given at the first examination. The differences could have clinical consequences and result in incorrect image interpretations.3 IntroductionMyocardial perfusion scintigraphy with single-photon emission tomography (SPET) is a method that is widely used to assess ischaemic heart diseases (1). Such investigations are carried out by combining a rest study and a stress study that are performed either on the same day or on two separate days (2-5). A one-day protocol can be performed either as a stress-rest or a rest-stress combination. Performing a complete study on a single day is of advantage logistically, as well as providing better communication between the patient and the staff. A known potential problem when performing two studies on the same day is that the residual activity from the first study contributes to the activity measured in the second study (2). In order to minimize the effect of this unwanted contribution, a larger amount of activity must be administered to the patient during the second study. The relationship between the activities administered in the two studies is often 300:900 MBq and the total amount is limited by national regulations. This means that there is a tradeoff between the image quality in terms of a high signal-to-noise ratio in the first study and the unwanted contribution from the residual activity from this study in the second study. Clinical studies support the usefulness of both one-day and two-day protocols (2-4;6), but a detailed comparison of these protocols has, to our knowledge, not been performed previously.

Optimized Energy Window Configuration for 201Tl Imaging

“…The number and distribution of the primary and scattered photons in the simulation study were similar to those in a typical clinical study (21). Moreover, the results of the present study were also evaluated with data from some real patients.…”

“…The activity distributions in the organs of the phantom were adjusted on the basis of the 201 Tl uptake of the organs in a healthy person (21). Two small defects were fabricated on the lateral and inferoapical regions of the cardiac left ventricle.…”

A model that accounts for the interdependence of extent and severity in the automatic evaluation of myocardial defects

“…Physical effects, such as photon attenuation, contribution from photons scattered in the patient and distance-dependent collimator resolution blurring, were included in the simulated SPECT projections. The number of simulated photon histories per projection was sufficient to obtain good image quality [14]. Each of the projections was scaled in counts to match a 1 day rest : stress 99m Tc-sestamibi protocol (300 : 900 MBq with a separation time of 3 h).…”

Subendocardial versus transmural ischaemia in myocardial perfusion SPECT – a Monte Carlo study

“…The SPECT projections were stored as 64 · 64 float matrices with a pixel size of 0AE63 · 0AE63 cm 2 . The projections were then scaled to match a 2-day stress-rest protocol (El-Ali et al, 2005a) assuming an administered activity of 600 MBq 99m Tc-sestamibi (for both stress and rest studies), an acquisition time of 20 s per projection, and an activity uptake in the heart of 9 MBq (1AE5%). The projections of heart images at rest and during stress were scaled by the same activity uptake fraction in this study.…”