Pinhole SPECT shows promise for arthritis imaging

Jul 21, 2005

Multipinhole SPECT has long been used as a technique for preclinical animal imaging. In its most common application, the parallel-hole collimator for planar SPECT is replaced with a pinhole collimator on a rotating gamma camera system. In the past few years, the technique has been introduced into the clinical setting, with prospective studies performed in parathyroid imaging, scintimammography, and ankle imaging.

The advantage of multipinhole SPECT imaging is that more pinholes mean higher count rates, and higher count rates mean faster image acquisition times. In addition, because geometric sensitivity increases for points close to the pinhole, small-diameter and high-magnification pinhole geometries may be useful for some imaging tasks when used with large-field-of-view scintillation cameras.

A research team from the Central Institute for Electronics of the Research Center Jülich in Jülich, Germany, and the department of nuclear medicine at the University of Düsseldorf in Germany is currently examining the use of a high-resolution, high-sensitivity, multipinhole SPECT system in the diagnosis of arthritic hands. The initial findings from their work in progress, displayed in a poster presentation at the Society of Nuclear Medicine (SNM) in Toronto last month, showed promise that the technique may find a place in the armamentarium of arthritis imaging.

The group has developed a multiplexing multipinhole imaging technique called HiSPECT, which is commercially available through Bioscan of Washington, DC. The researchers claim that the technology provides a substantial increase in sensitivity while maintaining the resolution benefits of pinhole SPECT.

"The multiplexing or overlapping projection pattern provides a more efficient coverage of the detector and an increase in sensitivity across the field-of-view," they wrote.

The researchers upgraded a Picker (acquired by Philips Medical Systems in 2001) dual-head Prism 2000 gamma camera with a nine-pinhole focusing hand aperture. The detector on the unit is a 6.5 mm-thick Nal crystal with an active area of 220 mm x 240 mm and an intrinsic resolution near 3.6 mm. They used a pyramidal collimator with a depth of 152.5 mm, and typically performed their hand studies at a radius of 90 mm.

The group quantified the resolution and sensitivity of its HiSPECT system through imaging a Jaszczak phantom using the dedicated hand aperture. They reported an average sensitivity of greater than 150 cps/MBq with a reconstructed resolution near 2.5 mm.

"The locations and tilts of the pinholes were chosen such that one serves as a focusing aperture with a cylindrical field-of-view of 110 mm x 110 mm while the other full-hand aperture images a cylindrical field-of-view of 110 mm x 200 mm," the study authors wrote.

The patients (10 with osteoarthritis, 10 with early signs of rheumatoid arthritis, and 10 control subjects) were injected with technetium-99 labeled either with methylene diphosphonate or hydroxyl diphosphonate, according to the researchers.

"In addition to HiSPECT measurements, three-phase scintigraphy and radiographs were performed with all patients, and MR images were taken and registered with corresponding SPECT images in selected rheumatoid arthritis patients," they wrote.

As part of ongoing research, the team exhibited the results of a rheumatoid arthritis study conducted with the new technology. A 44-year-old female with early stage rheumatoid arthritis was injected with 500 MBq of technetium-99, and 15 projections of 80 seconds each were acquired four hours after injection for HiSPECT measurement. Her hand was fixed in position with a plastic-glass device to allow for postmeasurement image fusion. A T1-weighted MR image of the hand was also acquired.

The group reported that no signs of bone erosion appeared in the MRI, but the multi-pinhole SPECT image showed signs of increased bone metabolism in regions of diagnostic interest. Although more study is needed, the researchers wrote that their technique may provide the sensitivity and resolution required for clinical hand imaging.

By Jonathan S. Batchelor
AuntMinnie.com staff writer
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