Evaluation of brain activity in FDG PET studies.

PURPOSE: A tool (Gemini) was developed for quantifying regions of interest (ROIs) in registered MR and PET data. Its use was validated through phantom and simulated studies. METHOD: Hot spheres were imaged in a phantom (3:1 and 5:1 target-to-nontarget ratios). The computerized 3D Hoffman brain phantom was used to simulate PET studies. Spherical local activity features of two diameters (4 and 10 mm) and five intensities (5, 15, 25, 50, and 100% increase over gray matter) were added to the data in the thalamus and Brodmann area 37. The data were reprojected into sinograms and blurred with a 7 mm kernel. Poisson noise was added, and the sinograms were then reconstructed and analyzed using both SPM96 and Gemini spherical ROIs. RESULTS: Based on phantom and simulated data, the 95th percentile of intensity within a Gemini ROI afforded a reasonable joint optimization of variance (reliability) and accuracy (validity). SPM96 and Gemini results were similar for the larger (10 mm) feature, but in this application, Gemini was more sensitive than SPM96 for the small feature (4 mm). CONCLUSION: Gemini, a tool for display and measurement of spherical ROIs in registered PET and MR data, is precise and accurate for testing hypotheses of differences in localized brain activity, comparing favorably with SPM96.

Intermodality, retrospective image registration in the thorax.

UNLABELLED: The purpose of this study was to develop an accurate, retrospectively applicable procedure for registering thoracic studies from different modalities in a short amount of time and with minimal operator intervention. METHODS: CT and PET studies were acquired from six patients. The pleural surfaces in both image sets were determined by segmenting based on 50% of the maximum soft-tissue value in the study. These surfaces were converted into three-dimensional volumes and used to register the CT and PET studies in three dimensions using a sum of least squares fitting approach. The registered PET study was then displayed in a hot metal scale overlayed on top of the gray scale CT study. The accuracy of the fit was evaluated through a phantom study and preliminary clinical evaluation. RESULTS: A phantom study was performed to determine the limits of this technique. The accuracy was determined to be less than 2.3 mm in the x and y direction and 3 mm in the z direction. Preliminary clinical evaluation was also performed with encouraging results. CONCLUSION: This technique accurately registers PET and CT images of the thorax, retrospectively, without the need for external fiducial markers or other a priori action.

Evaluation of emission-transmission registration in thoracic PET.

UNLABELLED: The intent of this investigation was to quantitate the amount of misregistration between PET emission and transmission scans of the thorax that occurs in a normal clinical environment. METHODS: The data from 17 FDG myocardial studies were evaluated. Prior to injection, a transmission study was acquired for 15 min using a 68Ge/68Ga ring source. The location of the cross-hairs from a laser alignment system was marked on the patient who was then removed from the scanner and injected with 10 mCi of FDG. After 45 min, the patient was placed back on the table and repositioned with the previously placed marks and a 15-min emission scan was acquired. The outline of the lungs on both the transmission and emission images was manually segmented. Both attenuation-corrected and noncorrected emission images were evaluated and the one that provided clearer visualization of the outline of the lungs was chosen for segmentation. The segmented contours of the transmission and emission scans were then registered with the method described by Pelizzari et al. using the transmission image as the "head" and the emission image as the "hat." The allowable transformations were x and y shifts and rotation in the transverse plane. RESULTS: Shifts in the x-axis averaged 2.4 mm (range: 0.2-7.3 mm, 80% less than 3.3 mm) with shifts in the y-axis averaging 2.6 mm (range: 0.1-8.7 mm, 80% less than 2.4 mm) and rotations in the transverse plane averaging 1.6 degrees (range: 0.2 to 5.1 degrees, 80% less than 2.4 degrees). A phantom study indicated that the accuracy of this method of evaluating misregistration was 2.35 mm and 1.81 mm in the x and y directions, respectively. CONCLUSION: Our preliminary evaluation indicates that careful application of laser alignment is an adequate method of registration in most cases.

Tolerance to and physical dependence on N-allylnormetazocine (NANM) in chronic spinal dogs.

Six female chronic spinal dogs were administered N-allylnormetazocine (NANM) chronically by the intravenous route starting at 0.3 mg/kg/day. The dose was escalated to a stabilization dose of 10 mg/kg/day. The dogs became tolerant to NANM's ability to produce canine delirium and its anorexigenic and respiratory stimulant effects. Naltrexone increased the amplitude of the flexor reflex and pulse rate in the body temperature, pupillary constriction, bradycardia and tachypnea. Appetite was decreased and weight was lost. These data indicate that chronic administration of NANM produces tolerance and a unique type of physical dependence. Some changes produced by chronically administered NANM were naltrexone antagonizable, others were not suggesting that NANM may have several mechanisms of action.

The effects of morphine- and nalorphine- like drugs in the nondependent and morphine-dependent chronic spinal dog.

Three different syndromes produced by congeners of morphine have been identified in the nondependent chronic spinal dog. These syndromes have been attributed to interaction of agonists with three distinguishable receptors (mu, kappa and sigma). Morphine is the prototype agonist for the mu receptor, ketocyclazocine for the kappa receptor and SKF-10,047 for the sigma receptor. The morphine syndrome (mu) in the dog is characterized by miosis, bradycardia, hypothermia, a general depression of the nociceptive responses and indifference to environmental stimuli. Ketocyclazocine (kappa) constricts pupils, depresses the flexor reflex and produces sedation but does not markedly alter pulse rate or the skin twitch reflex. SKF-10,047 (sigma), in contrast to morphine and ketocyclazocine, causes mydriasis, tachypnea, tachycardia and mania. The effects of these three drugs can be antagonized by the pure antagonist naltrexone, indicating that they are agonists. Further, chronic administration of morphine, ketocyclazocine and SKF-10,047 induces tolerance to their agonistic effects. Morphine suppresses abstinence in morphine-dependent dogs while ketocyclazocine does not. Ketocyclazocine at best precipitated only a liminal abstinence syndrome in the morphine-dependent dog, indicating that it had little affinity for the morphine receptor. Ketocyclazocine thus appears to be a selective agonist at the kappa receptor. Further, it has been shown that buprenorphine is a partial agonist of the mu type which both suppressed and precipitated abstinence in the morphine-dependent dog while morphine and propoxyphene are stronger agonists. Apomorphine and SKF-10,047 produce similar pharmacologic effects suggesting that sigma activity may involve a dopaminergic mechanism.