Christian Boy

Body ownership refers to the special perceptual status of one's own body, which makes bodily sensations seem unique to oneself. We studied the neural correlates of body ownership by controlling whether an external object was accepted as part of the body or not. In the rubber hand illusion (RHI), correlated visuotactile stimulation causes a fake hand to be perceived as part of one's own body. In the present study, we distinguished between the causes (i.e., multisensory stimulation) and the effect (i.e., the feeling of ownership) of the RHI. Participants watched a right or a left rubber hand being touched either synchronously or asynchronously with respect to their own unseen right hand. A quantifiable correlate of the RHI is a shift in the perceived position of the subject's hand toward the rubber hand. We used positron emission tomography to identify brain areas whose activity correlated with this proprioceptive measure of body ownership. Body ownership was related to activity in the right posterior insula and the right frontal operculum. Conversely, when the rubber hand was not attributed to the self, activity was observed in the contralateral parietal cortex, particularly the somatosensory cortex. These structures form a network that plays a fundamental role in linking current sensory stimuli to one's own body and thus also in self-consciousness.

UNLABELLED: Radiolabeled somatostatin analogs represent valuable tools for both in vivo diagnosis and therapy of neuroendocrine tumors (NETs) because of the frequent tumoral overexpression of somatostatin receptors (sst). The 2 compounds most often used in functional imaging with PET are (68)Ga-DOTATATE and (68)Ga-DOTATOC. Both ligands share a quite similar sst binding profile. However, the in vitro affinity of (68)Ga-DOTATATE in binding the sst subtype 2 (sst2) is approximately 10-fold higher than that of (68)Ga-DOTATOC. This difference may affect their efficiency in the detection of NET lesions because it is the sst2 that is predominantly overexpressed in NET. We thus compared the diagnostic value of PET/CT with both radiolabeled somatostatin analogs ((68)Ga-DOTATATE and (68)Ga-DOTATOC) in the same NET patients. METHODS: Forty patients with metastatic NETs underwent (68)Ga-DOTATOC and (68)Ga-DOTATATE PET/CT as part of the work-up before prospective peptide receptor radionuclide therapy. The performance of both imaging methods was analyzed and compared for the detection of individual lesions per patient and for 8 defined body regions. A region was regarded positive if at least 1 lesion was detected in that region. In addition, radiopeptide uptake in terms of the maximal standardized uptake value (SUVmax) was compared for concordant lesions and renal parenchyma. RESULTS: Seventy-eight regions were found positive with (68)Ga-DOTATATE versus 79 regions with (68)Ga-DOTATOC (not significant). Overall, however, significantly fewer lesions were detected with (68)Ga-DOTATATE than with (68)Ga-DOTATOC (254 vs. 262, P < 0.05). Mean (68)Ga-DOTATATE SUVmax across all lesions was significantly lower than (68)Ga-DOTATOC (16.0 ± 10.8 vs. 20.4 ± 14.7, P < 0.01). Mean SUVmax for renal parenchyma was not significantly different between (68)Ga-DOTATATE and (68)Ga-DOTATOC (12.7 ± 3.0 vs. 13.2 ± 3.3). CONCLUSION: (68)Ga-DOTATOC and (68)Ga-DOTATATE possess a comparable diagnostic accuracy for the detection of NET lesions, with (68)Ga-DOTATOC having a potential advantage. The approximately 10-fold higher affinity for the sst2 of (68)Ga-DOTATATE does not prove to be clinically relevant. Quite unexpectedly, SUVmax of (68)Ga-DOTATOC scans tended to be higher than their (68)Ga-DOTATATE counterparts.

OBJECTIVE: Aripiprazole at clinically effective doses occupies some 90% of striatal dopamine 2 and 3 (D(2)/D(3)) receptors. In order to further characterize its extrastriatal and time-dependent binding characteristics, the authors conducted positron emission tomography (PET) studies with the D(2)/D(3) antagonist [(18)F]fallypride at varying time points after the last aripiprazole administration in patients with schizophrenia. METHOD: Sixteen inpatients with a DSM-IV diagnosis of schizophrenia or schizoaffective disorder receiving treatment with aripiprazole underwent an [(18)F]fallypride PET scan. Receptor occupancy was calculated as the percentage reduction in binding potential relative to unblocked values measured in eight age-matched, medication-free patients with schizophrenia. In addition, aripiprazole serum concentrations were determined as part of a routine therapeutic drug monitoring program in a large group of patients (N=128) treated with aripiprazole. RESULTS: Mean dopamine D(2)/D(3) receptor occupancy was high in all brain regions investigated, with no binding difference across brain regions. Nonlinear regression analysis revealed maximum attainable receptor occupancy (E(max)) values close to saturation. The values for serum concentration predicted to provide 50% of E(max) (EC(50)) were in the range of 5-10 ng/ml in all brain regions. The D(2)/D(3) receptors were completely saturated when serum aripiprazole concentration exceeded 100-150 ng/ml. The mean concentration in the large clinical patient sample was 228 ng/ml (SD=142). CONCLUSIONS: Because of its high affinity for D(2)/D(3) receptors and its long elimination half-life, aripiprazole at clinical doses occupies a high fraction of its target receptor everywhere in the brain. Its dissociation from those receptors is very slow, such that the authors calculate from the results that in patients with serum aripiprazole concentrations in the range typical for clinical practice, D(2)/D(3) receptors must remain nearly saturated for as long as 1 week after the last dose.

CONTEXT: Malignant melanoma has become an increasing interdisciplinary public health challenge worldwide. Sentinel lymph node excision (SLNE) is considered the most sensitive and specific staging test for the detection of micrometastatic melanoma in regional lymph nodes. OBJECTIVE: To compare metastatic node detection and disease-free survival using single-photon emission computed tomography/computed tomography (SPECT/CT)-aided SLNE vs standard SLNE in patients with melanoma. DESIGN, SETTING, AND PATIENTS: A prospective, computerized melanoma patient database at the University Hospital Essen, Skin Cancer Center, Essen, Germany, was used to identify a cohort of 464 patients eligible for SLNE between March 2003 and April 2011. A total of 403 patients with clinically negative lymph nodes, who underwent SLNE with or without preoperative SPECT/CT, qualified for subsequent analysis. MAIN OUTCOME MEASURES: Metastatic node detection and disease-free survival. RESULTS: Between March 2003 and October 2008, 254 patients underwent the standard SLNE technique. After November 2008, 149 patients underwent the SPECT/CT technique. Patients who did not receive SNLE in both intervals (46/300 [15.34%] for standard cohort vs 15/164 [9.15%] for SPECT/CT cohort; P = .06) did not differ in either age (difference, 69.20 years; 95% CI, 62.84-72.07 years; P = .38), tumor depth (difference, 2.90 mm; 95% CI, 2.87-4.54 mm; P = .54), or ulceration of the primary tumor (difference, -8.00%; 95% CI, -35.74% to 19.81%; P = .59). However, using SPECT/CT allowed SLNE in the head and neck area more frequently (2.0% for standard vs 23.5% for SPECT/CT; difference, 21.1%; 95% CI, 14.1%-28.2%; P < .001). In the SPECT/CT cohort, more sentinel lymph nodes per patient were detected than in the standard cohort (2.40 vs 1.87; 95% CI, 1.93-2.18; P < .001). The number of positive sentinel lymph nodes per patient was significantly higher in the SPECT/CT cohort than in the standard cohort (0.34 vs 0.21; 95% CI, 0.21-0.31; P = .04). The local relapse rate in the SPECT/CT cohort was lower than in the standard cohort (6.8% vs 23.8%, P = .03), which prolonged 4-year disease-free survival (93.9% vs 79.2%; P = .02). CONCLUSION: Among patients with clinically lymph node-negative melanoma, the use of SPECT/CT-aided SLNE compared with SLNE alone was associated with a higher frequency of metastatic involvement and a higher rate of disease-free survival.