Experimental validation of estimated spatially variant radioisotope-specific point spread functions using published positron range simulations and fluorine-18 measurements.

In this work we compare spatially variant radioisotope-specific point spread functions (PSFs) derived from published positron range data with measured data using a high resolution research tomograph (HRRT). Spatially variant PSFs were measured on a HRRT for fluorine-18, carbon-11 and gallium-68 using an array of printed point sources. For gallium-68, this required modification of the original design to handle its longer positron range. Using the fluorine-18 measurements and previously published data from Monte-Carlo simulations of positron range, estimated PSFs for carbon-11 and gallium-68 were calculated and compared with experimental data. A double 3D Gaussian function was fitted to the estimated and measured data and used to model the spatially varying PSFs over the scanner field of view (FOV). Differences between the measured and estimated PSFs were quantified using the full-width-at-half-maximum (FWHM) and full-width-at-tenth-maximum (FWTM) in the tangential, radial and axial directions. While estimated PSFs were generally in agreement with the measured PSFs over the entire FOV better agreement was observed (FWHM and FWTM differences of less than 10%) when using one of the two sets of positron range simulations, especially for gallium-68 and for the FWTM. Spatially variant radioisotope specific PSFs can be accurately estimated from fluorine-18 measurements and published positron range data. We have experimentally validated this approach for carbon-11 and gallium-68, and such an approach may be applicable to other radioisotopes such as oxygen-15 for which measurements are not practical.

Rapid Rechallenge with Clozapine Following Pronounced Myocarditis in a Treatment-Resistant Schizophrenia Patient.

Clozapine is an atypical antipsychotic which is often effective in patients who fail to respond to other antipsychotics, but its use carries substantial risk. Myocarditis is one of the life-threatening adverse effects, which occurs in about 1% of exposed patients. Rechallenge with clozapine is controversial, particularly shortly after the occurrence of the myocarditis, and when there is clear and convincing evidence of cardiac damage. Aggressive use of clozapine, however, may be critical for the recovery of patients early in the course of their illness. Here we report a successful case of clozapine rechallenge following an initial aggressive dosage titration in an inpatient setting.

Rapid Re-challenge with Clozapine Following Pronounced Myocarditis in a Treatment-Resistance Schizophrenia Patient.

Clozapine is an atypical antipsychotic which is often effective in patients who fail to respond to other antipsychotics, but its use carries substantial risk. Myocarditis is one of the life-threatening adverse effects which occurs in about 1% of exposed patients. Re-challenge with clozapine is controversial, particularly shortly after the occurrence of the myocarditis and when there is clear and convincing evidence of cardiac damage. Aggressive use of clozapine, however, may be critical for the recovery of patients early in the course of their illness. Here we report a successful case of clozapine rechallenge following an initial aggressive dosage titration in an inpatient setting.