Optimization of injected 68Ga-PSMA activity based on list-mode phantom data and clinical validation.

Optimization of injected gallium-68 (68Ga) activity for 68Ga-prostate-specific membrane antigen positron emission tomography/computed tomography (68Ga-PSMA PET/CT) studies is relevant for image quality, radiation protection, and from an economic point of view. However, no clear guidelines are available for 68Ga-PSMA studies. Therefore, a phantom study is performed to determine the highest coefficient of variation (COV) acceptable for reliable image interpretation and quantification.To evaluate image interpretation, the relationship of COV and contrast-to-noise ratio (CNR) was studied. The CNR should remain larger than five, according to the Rose criterion. To evaluate image quantification, the effect of COV on the percentage difference (PD) between quantification results of two studies was analyzed. Comparison was done by calculating the PD of the SUVmax. The maximum allowable PDSUVmax was set at 20%. The highest COV at which both criteria are still met is defined as COVmax. Of the NEMA Image Quality phantom, a 20 min/bed (2 bed positions) scan was acquired in list-mode PET (Philips Gemini TF PET/CT). The spheres to background activity ratio was approximately 9:1. To obtain images with different COV, lower activity was mimicked by reconstructions with acquisition times of 10 min/bed to 5 s/bed. Pairs of images were obtained by reconstruction of two non-overlapping parts of list-mode data.For the 10-mm diameter sphere, a COV of 25% still meets the criteria of CNRSUVmean ≥ 5 and PDSUVmax ≤ 20%. This phantom scan was acquired with an acquisition time of 116 s and a background activity concentration of 0.71 MBq/kg. Translation to a clinical protocol results in a clinical activity regimen of 3.5 MBq/kg min at injection. To verify this activity regimen, 15 patients (6 MBq/kg min) with a total of 22 lesions are included. Additional reconstructions were made to mimic the proposed activity regimen. Based on the CNRSUVmax, no lesions were missed with this proposed activity regimen.For our institution, a clinical activity regimen of 3.5 MBq/kg min at injection is acceptable, which indicates that activity can be reduced by almost 50% compared with the current code of practice. Our proposed method could be used to obtain an objective activity regimen for other PET/CT systems and tracers.

What is the value of emission tomography studies in patients with a primary glioblastoma multiforme treated by 192Ir brachytherapy?

BACKGROUND: We studied the use of (201)Thallium SPECT and L-[1-(11)C]-tyrosine PET in patients with a primary glioblastoma multiforme treated with (192)Ir brachytherapy after surgery and external beam radiation therapy. We hypothesised that the patients most likely to benefit from further surgery after deterioration would be those with radiation necrosis and would be recognised by a negative emission tomography scan. METHODS: Twenty-one patients underwent (201)Thallium SPECT performed before brachytherapy, and this was repeated in 19 patients when recurrence was suspected. Nine patients also underwent a PET scan at the same time. Nine patients underwent a second operation. FINDINGS: SPECT and PET were highly concordant concerning the prediction of radionecrosis and/or tumour recurrence. Repeat surgery did not lead to a significant increase in survival. There was no significant association between the duration of survival and tumour-to-background ratio but the number studied was small. Both SPECT and PET showed highly active lesions, which were proved to be recurrent tumour by clinical and histological follow-up. CONCLUSION: Although PET and SPECT are both highly sensitive in detecting active tumour tissue, emission tomography was not clinically valuable in the investigation of patients with a primary glioblastoma treated with brachytherapy.

Effects of psychotherapy on regional cerebral blood flow during trauma imagery in patients with post-traumatic stress disorder: a randomized clinical trial.

BACKGROUND: Functional brain-imaging studies in post-traumatic stress disorder (PTSD) have suggested functional alterations in temporal and prefrontal cortical regions. Effects of psychotherapy on these brain regions have not yet been examined. METHOD: Twenty civilian PTSD out-patients and 15 traumatized control subjects were assessed at baseline using psychometric ratings. Cerebral blood flow was measured using trauma script-driven imagery during 99mtechnetium hexamethyl-propylene-amine-oxime single-photon emission computed tomography scanning. All 20 out-patients were randomly assigned to treatment or wait-list conditions. Treatment was brief eclectic psychotherapy (BEP) in 16 weekly individual sessions. RESULTS: At baseline, greater activation was found in the right insula and right superior/middle frontal gyrus in the PTSD group than in the control group. PTSD patients treated with BEP significantly improved on all PTSD symptom clusters compared to those on the waiting list. After effective psychotherapy, lower activation was measured in the right middle frontal gyrus, compared to the PTSD patients on the waiting list. Treatment effects on PTSD symptoms correlated positively with activation in the left superior temporal gyrus, and superior/middle frontal gyrus. CONCLUSIONS: BEP induced clinical recovery in PTSD patients, and appeared to modulate the functioning of specific PTSD-related sites in the prefrontal cortical regions.