Detectability of small objects in PET/computed tomography phantom images with Bayesian penalised likelihood reconstruction.

OBJECTIVES: This study investigated the subcentimetre lesion detection gains of a Bayesian penalised likelihood reconstruction (BPLR) (Q.Clear, GE Healthcare, Milwaukee, USA) in PET/computed tomography (CT) phantom images and compares observer performance with ordered subset expectation maximisation (OSEM) reconstruction images (VUE Point HD, GE Healthcare). METHODS: Images were presented to three blinded experienced observers to identify lesions and assign confidence ratings. Responses were analysed using jackknife alternative free receiver operator characteristic (JAFROC) software. Phantom lesions (active and nonactive) were constructed using putty. Seventy nonactive and 93 (F) active lesions, with diameters of 3, 5 or 7 mm were suspended in active backgrounds at varying contrast ratios (2:1-32:1) within an National Electrical Manufacturers Association 2012 phantom. PET/CT images were acquired with a GE Discovery 710 and reconstructed using both BPLR (penalisation coefficient 400) and high-definition attenuation corrected (HDAC) OSEM (2 iterations, 24 subsets). RESULTS: Small but significant (P = 0.009) visual detection gains were seen for active lesions with BPLR [weighted JAFROC figure of merit (wJAFROC FOM) = 0.77] over OSEM (FOM = 0.74). When split by subset, these improvements were significant for 5 mm and lesion to background ratio of 8:1. No significant (P = 0.514) differences were seen for the identification of nonactive lesions of any size (BPLR FOM = 0.74 and OSEM FOM = 0.73). CONCLUSIONS: Significant detection gains were demonstrated for small active lesions with BPLR over OSEM. Coupled with the significant increase in contrast-to-noise ratio, these results support the use of BPLR in the imaging of small active (≤7 mm) lesions but show no improvement with BPLR in the identification of true negative lesions.

Improvement in DMSA imaging using adaptive noise reduction: an ROC analysis.

Dimercaptosuccinic acid imaging is the 'gold standard' for the detection of cortical defects and diagnosis of scarring of the kidneys. The Siemens planar processing package, which implements adaptive noise reduction using the Pixon algorithm, is designed to allow a reduction in image noise, enabling improved image quality and reduced acquisition time/injected activity. This study aimed to establish the level of improvement in image quality achievable using this algorithm. Images were acquired of a phantom simulating a single kidney with a range of defects of varying sizes, positions and contrasts. These images were processed using the Pixon processing software and shown to 12 observers (six experienced and six novices) who were asked to rate the images on a six-point scale depending on their confidence that a defect was present. The data were analysed using a receiver operating characteristic approach. Results showed that processed images significantly improved the performance of the experienced observers in terms of their sensitivity and specificity. Although novice observers showed significant increase in sensitivity when using the software, a significant decrease in specificity was also seen. This study concludes that the Pixon software can be used to improve the assessment of cortical defects in dimercaptosuccinic acid imaging by suitably trained observers.

The suitability of gamma camera coincidence systems for nitrogen 13-labeled ammonia myocardial perfusion imaging: a quantitative comparison with full-ring PET.

BACKGROUND: The aim of this study was to examine the quality of nitrogen 13-labeled ammonia (NH(3)) perfusion data from coincidence-capable gamma camera positron emission tomography (GC-PET) systems compared with that from full-ring positron emission tomography (FR-PET). METHODS AND RESULTS: The performance parameters of the GC-PET system were examined and found adequate for imaging at the activity levels used clinically. We studied 15 patients who underwent stress and rest N-13-labeled NH(3) perfusion imaging on FR-PET and GC-PET systems. Quantitative analysis of perfusion values showed that GC-PET uptake was significantly lower than FR-PET uptake in 67.6% of segments. Bland-Altman analysis showed that the mean difference between FR-PET and GC-PET values was from 5.3% to 5.9%. Stress FR-PET identified 49 segments as having impaired perfusion, 46 (93.9%) of which were also identified by GC-PET. Fifty-six additional segments were identified as abnormal by GC-PET. These findings indicated a general overestimation of defect size on GC-PET. Analysis of the degree of perfusion reduction also found that GC-PET tended to overestimate defect contrast. These findings are similar to those previously found by workers examining fluorine 18-fluorodeoxyglucose uptake by both techniques. CONCLUSIONS: Good concordance was shown between GC-PET and FR-PET systems for N-13-labeled NH(3) perfusion imaging, although further work is required to optimize the technique.