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Photon Energy Recovery for Crosstalk Correction in Simultaneous ^99mTc/²⁰¹Tl Imaging

Centre d'Imagerie Nucléaire, Annecy
Service de Médecine Nucléaire, Épinal, France
Department of Medical Physics and Imaging, Cedars-Sinai Medical Center, Los Angeles, California

Correspondence: For correspondence or reprints contact: Pascal Hannequin, MD, PhD, Centre d'Imagerie Nucléaire, 4 Chemin de la Tour de la Reine, 74000 Annecy, France.

ABSTRACT

Simultaneous ^99mTc sestamibi/²⁰¹Tl imaging enables the acquisition of images of myocardial stress perfusion and myocardial viability in a single process. One of the major limits of this technique is the crosstalk of the ^99mTc downscattered photons into the ²⁰¹Tl window. We propose using the spectral deconvolution technique photon energy recovery (PER) for correcting this crosstalk. Methods: A planar line phantom made of ^99mTc vertical lines and ²⁰¹Tl horizontal lines and a cardiac SPECT phantom including an anterior (2 mL) and an inferior (1.5 mL) myocardial fixed defect were used. The phantoms were filled with an initial ^99mTc/²⁰¹Tl ratio of 5:1. Several successive acquisitions were made from time t = 0 to time t = 48 h (^99mTc/²⁰¹Tl ratio 0) without moving the phantoms. Total number of counts, contrast, and normalized SD (NSD) were calculated on the Tl-raw and the TI-PER planar images. SPECT datasets were analyzed. The Tl-raw images recorded at 48 h were considered the reference "virgin" ²⁰¹Tl images. Results: Total number of counts, contrast, and NSD ranged from 336% to 201 %, 15% to 29%, and 257% to 225% of the virgin ²⁰¹Tl values, respectively, for Tl-raw planar images; whereas values for TI-PER images ranged from 128% to 108%, 61% to 79%, and 154% to 108%, respectively. Anterior and inferior defect contrasts ranged from 1.18 to 1.22 and 1.12 to 1.16 for Tl-raw SPECT images, respectively; whereas for TI-PER images, value ranges were 1.28-1.32 and 1.211.24, respectively. The corresponding reference virgin ²⁰¹Tl values were 1.31 and 1.25 respectively. Summed score, average defect severity, and average defect extent ranges were 4–5, 0.4–0.52, and 4.7–5.9 for Tl-raw images, respectively, and 8–9, 0.59–0.79, and 7.4–8.8 for TI-PER images. The reference virgin ²⁰¹Tl values were 9, 0.73, and 8.7, respectively. Conclusion: PER is quantitatively efficient to remove ^99mTc crosstalk photons from ²⁰¹Tl images for ^99mTc/²⁰¹Tl ratios ranging from 5:1 to 2:1.

Key Words: simultaneous dual-isotope imaging • crosstalk correction • ^99mTc-sestamibi • ²⁰¹Tl • SPECT