First introduced at the 2007 SNM conference, high-definition PET (HD-PET, Siemens Healthcare, Malvern, PA) was designed to correct for distortions caused by the circular geometry of commercial PET scanners, according to Ludovic Le Meunier, a Siemens employee based at Cedars-Sinai Medical Center in Los Angeles, where the system is being used.

The high-definition technique involves the use of a point source of radiation that's mounted on a 3D robot to measure point-spread functions across the field-of-view of an image to correct for distortions. Dedicated software is then used to reconstruct images, resulting in improved signal-to-noise ratios and uniform spatial resolution of 2 mm, compared to spatial resolution of 4.5 to 5 mm for filtered back projection (FBP) reconstruction and about 5 mm for ordered subset expectation maximization (OSEM) algorithms, Le Meunier said in a presentation on Sunday.

Although high-definition PET was originally targeted at oncology imaging, Le Meunier and Cedars-Sinai researchers decided to test the technique in cardiac imaging. They used high-definition PET in two groups of patients: 15 patients referred for resting cardiac perfusion assessment with rubidium-82 and 14 patients referred for myocardial viability assessment with fluorine-18 FDG.

Scans were performed on a Biograph 64 TruePoint PET/CT system (Siemens Healthcare), and images reconstructed with HD-PET were compared to three other reconstruction techniques: FBP, 2D attenuation-weighted OSEM (AWOSEM), and 3D AWOSEM. Cedars-Sinai's QPET software was used to analyze images for automatic detection of the left ventricle and reorientation of the heart and quantitative analysis.

High-definition PET produces better quality PET images compared to three other image reconstruction techniques, thanks in part to better contrast-to-noise ratios, according to Ludovic Le Meunier. Image courtesy of the author.

The group found high-definition PET to be superior to the other reconstruction techniques in both the perfusion and viability patient groups. For the perfusion patients who received rubidium, the researchers saw contrast-to-noise ratio improvements as shown in the table below for static and gated patients:

Contrast-to-noise ratios, static versus gated perfusion patients Static Gated FBP 4.0 ± 1.7 1.6 ± 0.7 2D-AWOSEM 10.4 ± 4.4 4.1 ± 1.7 3D-AWOSEM 10.7 ± 4.0 4.1 ± 1.5 HD-PET 17.6 ± 5.9 7.0 ± 2.8 p-value < 0.05

Improvement was also seen in the viability patients who received FDG:

Contrast-to-noise ratios, static versus gated viability patients Static Gated FBP 7.9 ± 3.0 3.7 ± 1.3 2D-AWOSEM 25.6 ± 13.0 10.3 ± 4.1 3D-AWOSEM 27.7 ± 13.1 11.8 ± 5.4 HD-PET 44.9 ± 21.0 20.9 ± 9.8 p-value < 0.05

The group also saw declines in the average wall thickness and myocardial volume on high-definition PET studies, but these differences were not statistically significant. High-definition PET was equivalent to the other techniques for ejection fraction, wall motion, and wall thickening, Le Meunier said.

In a Tuesday presentation, Le Meunier discussed the use of high-definition PET with an application of the QPET software designed to compensate for motion in the beating heart. In a study of 10 patients, the researchers saw improvements in contrast-to-noise ratio with motion-frozen high-definition PET: 4.5 for standard reconstruction, 5.3 for HD-PET, and 7.4 for motion-frozen HD-PET. Motion-frozen HD-PET images also demonstrated narrower wall thickness and improved the detection of heart defects, he said.

By Brian Casey
AuntMinnie.com staff writer
June 17, 2009

Related Reading

Cedars-Sinai explores PET's future in nuclear cardiology, April 11, 2008

Rubidium PET/CT shows potential for coronary artery disease diagnosis, March 30, 2007

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