Adaptive scan duration in SPECT: Evaluation for radioembolization

Abstract

Purpose: It may be challenging to select the optimal scan duration for single-photon emission computed tomography (SPECT) protocols because the activity distribution characteristics can differ in every scan. Using simulations and experiments, we investigated whether the scan duration can be optimized for every scan separately by evaluating the activity distribution during scanning. We refer to this as adaptive scanning. Methods: The feasibility of adaptive scanning was evaluated for the detection of extrahepatic depositions in the pretreatment procedure of radioembolization, in which 99m Tc-labeled macroaggregated albumin ( 99m Tc-MAA) is injected into the liver. We simulated fast 1-min detector rotations and updated the reconstruction with the newly collected counts after every rotation. The scan was terminated when one of the two criteria was met: (a) when the mask difference of the detected extrahepatic deposition between two consecutive rotations was lower than 5%; or (b) when the reconstructed extrahepatic activity was negligible with respect to the total reconstructed activity (<0.075%). The performance of adaptive scanning was evaluated using a digital phantom with various activity distributions, a physical phantom experiment, and simulations based on 129 patient activity distributions. Results: The digital phantom data showed that the scan termination times substantially depended on the activity distribution characteristics. The experimental phantom data showed the feasibility of adaptive scanning with physical scanner measurements and illustrated that fast detector motion was not limiting the adaptive scanning performance. The patient data showed a large spread in the scan terminations times. By adaptive scanning, the mean scan duration of the patient distributions was shortened from 20 min (current clinical protocol) to 4.8 ± 0.2 min. The detection accuracy of extrahepatic depositions was unaffected and the mean difference in the extrahepatic deposition masks (compared with the 20-min scan) was only 7.0 ± 1.0%. Conclusion: Our study suggests that the SPECT scan duration can be personalized by assessing the activity distribution characteristics during scanning for the detection of extrahepatic depositions in the pretreatment procedure of radioembolization. The adaptive scanning approach might also be of benefit for other SPECT protocols, as long as a measure of interest is available for optimization.

Interventional respiratory motion compensation by simultaneous fluoroscopic and nuclear imaging: a phantom study

“…van der Velden et al (2019a) demonstrated that activity recoveries and the lung-shunting can be accurately retrieved when using faster acquisitions (using a one minute instead of 20 min scan duration; 20× more noise). Dietze et al (2020a) demonstrated that extrahepatic depositions could be accurately retrieved when using faster acquisitions (using a mean acquisition duration of five minutes instead of 20 min; 4× more noise). And Kunnen et al (2020) demonstrated that the use of lower activity levels can provide quantitative accurate results (imaging 100 MBq instead of 2 GBq 90 Y; 20× more noise).…”

Technical Note: Nuclear imaging with an x‐ray flat panel detector: A proof‐of‐concept study

“…However, some assumptions can be made based on current clinical care. For instance in radioembolization (which is of one the proposed applications for interventional SPECT scanning), it has been demonstrated that various quantitative measures (e.g., lung‐shunting fraction, tumor uptake ratio) can be accurately determined down to 1/10th of the clinically used number of counts 14‐16 . These findings suggest that the flat panel detector (which similarly has a lower count rate) should also be able to retrieve accurate clinical results.…”