Influence of downscatter in simultaneously acquired thallium-201/technetium-99m-PYP SPECT.
Simultaneously acquired dual-isotope imaging is a unique and useful approach in SPECT. Photon spillover, however, is a potential limitation of this technique.


METHODS
To investigate the degree of 99mTc downscatter into the 201Tl window in patients, simultaneously acquired dual-isotope 201Tl/99mTc-pyrophosphate imaging was performed in 17 patients with acute myocardial infarction (MI). Thallium-201 SPECT imaging was performed first, with a 201Tl photopeak window after the 201Tl injection (early 201Tl images), followed by 99mTc injection and SPECT acquisition using dual-isotope windows (dual 201Tl images). Twenty-four hours after the 99mTc injection, a third set of 201Tl images was obtained (24-hr 201Tl images). Thallium defect size (extent score) and defect severity (severity score) were calculated from these three sets of 201Tl images to quantify the MI.


RESULTS
Technetium-99m accumulation of varying intensity was recognized in all patients. Extent scores and severity scores were identical in early 201Tl images and 24-hr 201Tl images. Both scores, however, in the dual 201Tl images were decreased by 36% and 53%, respectively.


CONCLUSIONS
There in a considerable 99mTc downscatter into the 201Tl window, which prevents precise quantification of MI in simultaneously acquired dual-isotope 201Tl/99mTc-pyrophosphate imaging.
Ando
H
H
Division of Cardiology, Matsuyama Red Cross Hospital, Ehime, Japan.
Fukuyama
T
T
Mitsuoka
W
W
Egashira
S
S
Imamura
Y
Y
Masaki
H
H
Ashihara
T
T
D005260:Female; D006321:Heart / Q000000981:diagnostic imaging; D006801:Humans; D008297:Male; D008875:Middle Aged; D009203:Myocardial Infarction / Q000000981:diagnostic imaging*; D016698:Technetium Tc 99m Pyrophosphate; D013794:Thallium Radioisotopes; D013997:Time Factors; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods*
D013794:Thallium Radioisotopes; D016698:Technetium Tc 99m Pyrophosphate