JNC: SPECT with half-time, half-dose superior to full-time

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Both “half-time” and “half-dose” wide-beam reconstruction (WBR) software can provide myocardial perfusion SPECT quality superior to full-time ordered-subset expectation maximization (OSEM) software, with an associated decrease in scan acquisition time and patient radiation exposure, according to a study published online Feb. 2 in the Journal of Nuclear Cardiology.

WBR uses resolution recovery and noise modeling to cope with decreased SPECT count statistics. Because WBR processing reconstructs half the usual SPECT count statistics, DePuey E. Gordon, MD, professor of radiology at Columbia University College of Physicians and Surgeons in New York City, and colleagues postulated that image quality equivalent to a full-time acquisition could be achieved in either half the time or with half the radiopharmaceutical activity.

Gordon and colleagues performed rest and eight-frame gated post-stress myocardial perfusion SPECT in 156 consecutive patients following 333-444 and 1184-1480 MBq (9-12 and 32-40 mCi) Tc-99m sestamibi injections, respectively, with full-time (rest = 14 minutes; stress = 12.3 minutes) acquisitions.

The full-time SPECT was processed with OSEM software and half-time SPECT processed with the half count density WBR software. A subsequent group of 160 consecutive patients matched in gender, weight and chest circumference received half-dose rest and stress injections of 214.6 and 647.5 MBq (5.8 and 17.5 mCi) with full-time SPECT acquisitions.

Image quality was judged by myocardial count density and uniformity, endocardial edge definition, perfusion defect delineation, right ventricular visualization and background noise. Half-time and half-dose WBR image quality were both superior to standard full-time OSEM. There was no significant difference between the summed stress and rest scores for full-time OSEM vs. half-time WBR in 82 patients with perfusion defects, according to Gordon and colleagues.

“The most likely explanation for this difference is that in most patients the administered activity for the 'half-dose' protocol was actually greater than half that used for the 'full-dose' protocol,” wrote the authors.

With the half-dose protocol, patient radiation exposure could be reduced to approximately 5 to 6 mSv, according to Gordon and colleagues. This gives the opportunity to customize scan protocols to meet specific patient requirements. For example, in an elderly, arthritic or uncooperative patient unable to tolerate a 12- to 15-minute SPECT acquisition, a full radiopharmaceutical dose and reduced-time SPECT acquisition would be beneficial. Alternatively, in a younger patient in whom radiation exposure is a concern, a reduced radiopharmaceutical dose and full-time acquisition would be preferable, suggested Gordon and colleagues.