(18)F-FDG PET/MRI evaluation of retroperitoneal fibrosis: a simultaneous multiparametric approach for diagnosing active disease.

PURPOSE: The aim of this study was to evaluate integrated (18)F-FDG PET/MRI as a one-stop diagnostic procedure in the assessment of (active) idiopathic retroperitoneal fibrosis (RPF) METHODS: A total of 22 examinations comprising a PET/CT scan followed by a PET/MRI scan in 17 patients (13 men, 4 women, age 58 ± 11 years) with histopathologically confirmed RPF at diagnosis or during follow-up under steroid therapy were analysed in correlation with laboratory inflammation markers (ESR, CRP). The patient cohort was subdivided into two groups: 6 examinations in untreated and 16 in treated patients. Tissue formations in typically periaortic localization suggestive of RPF were visually and quantitatively evaluated. The PET analysis included the assessment of SUVmax and a qualitative score for FDG uptake in RPF tissue in relation to the uptake in the liver. MRI analysis included evaluation of the T2-weighted image signal intensity, contrast enhancement and diffusion restriction (ADC values). Mean values were compared using the Mann-Whitney U test. ADC, SUVmax and ESR values were correlated using Pearson's correlation. RESULTS: MRI analysis revealed restricted diffusion in 100 % and 56 %, hyperintense T2 signal in 100 % and 31 %, and contrast enhancement in the periaortic tissue formation suggestive of RPF in 100 % and 62.5 % in the untreated and treated patients, respectively. In the qualitative and quantitative PET analysis, statistically significant differences were found for mean FDG uptake scores (2.5 ± 0.8 in untreated patients and 1.1 ± 0.9 in treated patients) and mean SUVmax (7.8 ± 3.5 and 4.1 ± 2.2, respectively). A strong correlation was found between the ADC values and SUVmax (Pearson r -0.65, P = 0.0019), and between ESR and CRP values and SUVmax (both r = 0.45, P = 0.061). CONCLUSION: Integrated (18)F-FDG PET/MRI shows high diagnostic potential as a one-stop diagnostic procedure for the assessment of (active) RPF providing multiparametric supportive information.

Assessment of lesion response in the initial radioiodine treatment of differentiated thyroid cancer using 124I PET imaging.

UNLABELLED: (124)I PET/CT images from differentiated thyroid cancer patients were retrospectively analyzed to assess the relationship between absorbed radiation dose (AD) to lesions and their response after radioiodine therapy. METHODS: Patients received serial (124)I PET/CT scans before and after their first radioiodine treatment. The pretherapy PET data were used to segment the lesion volumes and to predict the therapy-delivered ADs after administration of the therapeutic (131)I activity. The segmentation method's lower volume limit of determinability was a sphere of 0.80 mL, which classified the lesions into a known-volume group (>0.80 mL) or a small-volume group (≤0.80 mL) with their respective average and minimum ADs. The posttherapy PET data were used to assess the lesion-based therapy success. In the known-volume group, the response rate was calculated on the basis of lesions that received average ADs above the generally accepted threshold of 85 Gy for metastases and 300 Gy for thyroid remnants (TRs) and was expressed as the percentage of completely responding lesions. In the small-volume group, the metastasis and TR responses were evaluated for 3 minimum-AD groups: 5 to 10 Gy (TR, 5 to 30 Gy), >10 to 85 Gy (TR, >30 to 300 Gy), and >85 Gy (TR, >300 Gy). Their response rates were calculated in terms of the percentage of completely responding lesions in each minimum-AD group. RESULTS: In total, 59 lesions in 17 patients were amenable to reliable volume estimation. The response rates were 63%, 88%, and 90% for lymph node metastases (LMs), pulmonary metastases, and TRs, respectively. The response rates of 168 small lesions in 34 patients were more than 82% for LMs and more than 91% for TRs in each of the 3 minimum-AD groups; all small pulmonary metastases responded completely. CONCLUSION: In the known-volume group, the response rate for TRs matched well with historical data derived using (131)I scintigraphy imaging, whereas the response rate for LMs was not as high as expected, which may be explained by too short a follow-up time for a few LMs and a higher sensitivity of PET imaging. Small lesions were treated effectively, suggesting that they are considerably smaller than 0.80 mL.

Chewing-gum stimulation did not reduce the absorbed dose to salivary glands during radioiodine treatment of thyroid cancer as inferred from pre-therapy (124)I PET/CT imaging.

BACKGROUND: The goal of this prospective study was to estimate the absorbed (radiation) doses to salivary glands in radioiodine therapy of thyroid cancer under chewing-gum stimulation using (124)I positron emission tomography (PET)/computed tomography (CT) imaging. METHODS: Duplex ultrasonography was conducted in three test persons for visual comparison of the glandular blood flow with three different stimulation types (no stimulation, chewing tasteless gum base, sucking on lemon slices). Ten patients with newly diagnosed differentiated thyroid cancer received (124)I PET/CT dosimetry after thyroidectomy and prior to radioiodine therapy. Patients underwent a series of three (124)I PET/CT scans (4, 24, and ≥96 h after administration of 23 MBq (124)I). They were instructed to chew gum base (tasteless) approximately 20 min after ingesting the (124)I-containing capsule in the course of the first day. Absorbed doses per administered (131)I activity to the salivary glands were calculated and compared with the previously published results of the lemon-juice stimulation and non-stimulation groups. RESULTS: The sonograms in the three test persons showed that glandular blood perfusion by lemon-juice stimulation was clearly increased compared with non-stimulation or chewing of gum base. The sonogram comparison between the chewing-gum stimulation and non-stimulation demonstrated a minor increase of blood flow for the gum base-stimulated salivary glands. The mean ± standard deviation of the absorbed dose per activity under chewing-gum stimulation for the submandibular and parotid glands (within parentheses) was 0.22 ± 0.09 Gy/GBq (0.22 ± 0.08 Gy/GBq). Compared with the absorbed doses of the non-stimulation group, 0.24 ± 0.08 Gy/GBq (0.21 ± 0.05 Gy/GBq), those of the chewing-gum stimulation group showed no significant change (P > 0.60), but the absorbed doses of the lemon-juice stimulation group, 0.35 ± 0.14 Gy/GBq (0.33 ± 0.09 Gy/GBq), were significantly higher (P < 0.04) than those of the chewing-gum stimulation group. CONCLUSIONS: The results suggest that salivary flow induced by chewing gum base does not cause a significant reduction of the salivary gland absorbed dose compared with that in the non-stimulation group. The increased blood flow appears to be a decisive factor causing the increased (131)I absorbed doses in the lemon-juice stimulation group.

S-ketamine and GABA-A-receptor interaction in humans: an exploratory study with I-123-iomazenil SPECT.

OBJECTIVE: We aimed to probe for regional cerebral effects of S-ketamine on in vivo GABA-A-receptor binding in healthy human subjects. METHODS: We investigated I-123-iomazenil SPECT before, during and after administration of S-ketamine in a blinded placebo-controlled study design (n = 12 in both groups). Analyses of SPECT were performed with voxel-based statistical parametric mapping (SPM), and statistical comparisons were made between the groups. We also assessed biochemical and behavioural changes during S-ketamine infusion. RESULTS: S-ketamine induced positive and negative symptoms measured by the Brief Psychiatric Rating scale (BPRS). It increased the cortisol and prolactin levels. Image analysis revealed significantly decreased I-123-iomazenil binding in bilateral dorsomedial prefrontal cortex during S-ketamine administration when compared to placebo. CONCLUSION: Our study delivers preliminary evidence for an in vivo interaction of S-ketamine with GABA-A-receptors in human dorsomedial prefrontal cortex.