An investigation of the Venetian blind effect.

When a rectangular wave grating is binocularly viewed with a neutral density filter over one eye, an illusory rotation resembling that of a partially opened Venetian blind is perceived (Cibis and Haber, 1951). Using a binary classification task, in the first experiment, the probability of perceiving a rotation in a given direction was measured as a function of a factorial combination of inter-ocular contrast (see Note 1) and luminance ratios. The probability of a rotation in a given direction decreased monotonically with the luminance of the brighter bars when the grating contains a less than unity contrast. This result is inconsistent with (i) the model of the Venetian blind effect proposed by Cibis and Haber (1951), (ii) a mechanism based on irradiation with a compressive non-linearity (von Helmholtz, 1911/1924, pp. 186-193) and (iii) contemporary stereo-energy/cross-correlation models of stereopsis. In the second and third experiments, we tested the prediction that irradiation combined with an early compressive non-linearity in response implies a positive relationship between both the threshold contrast or average luminance disparity to perceive rotation and the magnitude of perceived rotation, and the blur width at the bar's edge. No support was found for the prediction. We propose an intensity difference model of the probability of perceiving a rotation in a given direction as a function of the interocular difference in luminance or contrast.

Usefulness of 123I-MIBG scintigraphy in the evaluation of patients with known or suspected primary or metastatic pheochromocytoma or paraganglioma: results from a prospective multicenter trial.

UNLABELLED: Although (123)I-MIBG has been in clinical use for the imaging of pheochromocytoma for many years, a large multicenter evaluation of this agent has never been performed. The present study was designed to provide a prospective confirmation of the performance of (123)I-MIBG scintigraphy for the evaluation of patients with known or suspected primary or metastatic pheochromocytoma or paraganglioma. METHODS: A total of 81 patients with a prior history of primary or metastatic pheochromocytoma or paraganglioma and 69 with suspected pheochromocytoma or paraganglioma based on symptoms of catecholamine excess, CT or MRI findings, or elevated catecholamine or metanephrine levels underwent whole-body planar and selected SPECT 24 h after the administration of (123)I-MIBG. Images were independently interpreted by 3 masked readers, with consensus requiring agreement of at least 2 readers. Final diagnoses were based on histopathology, correlative imaging, catecholamine or metanephrine measurements, and clinical follow-up. RESULTS: Among 140 patients with definitive diagnoses (91, disease present; 49, disease absent), (123)I-MIBG planar scintigraphy had a sensitivity and specificity of 82%. For patients evaluated for suspected disease, sensitivity and specificity were 88% and 84%, respectively. For the subpopulations of adrenal (pheochromocytoma) and extraadrenal (paraganglioma) tumors, sensitivities were 88% and 67%, respectively. The addition of SPECT increased reader confidence but minimally affected sensitivity and specificity. CONCLUSION: This prospective study demonstrated a sensitivity of 82%-88% and specificity of 82%-84% for (123)I-MIBG imaging used in the diagnostic assessment of primary or metastatic pheochromocytoma or paraganglioma.

Influence of 99mTc-tetrofosmin SPECT myocardial perfusion imaging on the prediction of future adverse cardiac events.

BACKGROUND: The impact of myocardial perfusion imaging (MPI) on prediction of risk for future cardiac events was examined by comparing predictions based on clinical information alone and in combination with MPI findings. METHODS AND RESULTS: A 3-cardiologist Cardiac Event Prediction Panel (CEPP) estimated three-year cardiac event (non-fatal MI; aborted sudden cardiac death; cardiac death) risk based on clinical data (C) for 371 subjects. CEPP repeated this estimation after receiving Summed Stress Scores (SSS) and Summed Rest Scores (SRS) from blinded reading of rest-stress (99m)Tc-tetrofosmin MPI SPECT studies (C + MPI). The C and C + MPI estimates were then compared with three-year and total event rates. MPI was normal (SSS 13) in 77 (21%). Eighteen cardiac events occurred within 3 years and 33 occurred during a mean follow-up of 3.9 years. C + MPI estimates of low risk (<1-1.5%/year) identified significantly more patients who did not have events than C. C + MPI three-year event-rate predictions were more accurate than those made with C (P < .01). C + MPI categorization also provided better delineation of incremental risk on time-to-event analyses. CONCLUSIONS: (99m)Tc-tetrofosmin MPI single photon emission computed tomography (SPECT) findings significantly improve accuracy of cardiac event rate prediction compared to those based on clinical information alone.

(123)I-mIBG scintigraphy in patients with known or suspected neuroblastoma: Results from a prospective multicenter trial.

BACKGROUND: A prospective trial was conducted to confirm the diagnostic performance of (123)I-mIBG scintigraphy in patients with known or suspected neuroblastoma. PROCEDURE: One hundred patients (mean age 4.7 years) were enrolled, 86 with a previous diagnosis of neuroblastoma, 13 with suspected disease based upon symptoms, imaging findings, and elevated catecholamines, and one adult with an abdominal tumor thought to be of neuroendocrine origin. All patients underwent whole-body planar imaging 24 hr following IV administration of 1-10 mCi (37-370 MBq) (123)I-mIBG. SPECT imaging of the thorax/abdomen/pelvis was performed in 51 patients. Images were interpreted by three blinded readers, with consensus requiring agreement of at least two readers. Disease status was confirmed by histopathology, imaging results, catecholamine measurements, and follow-up. RESULTS: Sixty-four patients had active disease, 30 were without disease, and 6 were judged indeterminate because of insufficient confirmatory data. (123)I-mIBG scintigraphy had a sensitivity of 88% (56/64) and specificity of 83% (25/30). Sensitivity was 91% (30/33) among the subset of subjects who had both planar and SPECT imaging. Among 53 patients with recent histopathology, sensitivity and specificity were 93% and 92%, respectively. Most false-negative interpretations were in patients with minimal residual disease (n = 4), while false-positive interpretations generally involved atypical adrenal or other physiological uptake (n = 4). CONCLUSIONS: This prospective multicenter trial of (123)I-mIBG scintigraphy documents high sensitivity and specificity of this imaging technique in patients with both newly diagnosed and previously treated neuroblastoma.