Fan beam collimation with off center focus for simultaneous emission/transmission SPECT in multi-camera SPECT systems

Journal Article · Sun May 01 04:00:00 EDT 1994 · Journal of Nuclear Medicine

OSTI ID:197963

Hawman, E G; Ficaro, E P; Hamill, J J ^[1]

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1. Univ. of Michigan, Ann Arbor, MI (United States); and others

A practical method is introduced to overcome the truncation difficulties inherent in the centered fan beam/line source method of transmission scanning for SPECT attenuation correction. By offsetting the focal point of the fan beam collimator, the untruncated FOV can be increased. The maximum increase occurs when a marginal ray of the offset-fan collimator passes through the center-of-rotation, and gives a FOV nearly double that of a centered fan. Initial tests of the offset fan concept used a slit collimator Am-241 point source placed 62.5 cm away from the crystal face of an uncollimated gamma camera. The point source was located 18.25 cm to one side of the central axis. A 22.2 cm diameter cylindrical phantom with various inserts was imaged. Transmission projections were acquired with 3.2 mm sampling, 90 views in 360{degrees}. These projections were rebinned into a set of 45 parallel-beam projections in 180{degrees} and re-constructed by filtered back projection. Excellent images were obtained with no visible distortion or hot ring artifacts. The phantom was 6 cm off center, showing that a 34 cm FOV could be reconstructed without truncation distortions and without resorting to iterative reconstruction. Offset-fan designs for a triple headed SPECT system with 40 cm detectors show that an untruncated FOV of 37 cm diameter can be obtained. For dual-head cameras with 53 cm detectors, the FOV is 49 cm. Phantom and human studies were performed with an offset-fan collimator on a triple head SPECT system with simultaneous emission/transmission (Tl-201/Am-241) acquisition. The offset-fan beam design avoids truncation difficulties of the centered fan geometry for multi-head SPECT systems and provides the greater FOV needed for untruncated attenuation correction in cardiac SPECT studies.

• OSTI ID: 197963
• Report Number(s): CONF-940605--
• Journal Information: Journal of Nuclear Medicine, Journal Name: Journal of Nuclear Medicine Journal Issue: Suppl.5 Vol. 35; ISSN JNMEAQ; ISSN 0161-5505
• Country of Publication: United States
• Language: English

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