Search

Respiratory and cardiac motion artefacts impair the quality and reliability of medical imaging, particularly in nuclear medicine. At worst, the interpretation of distorted images may lead to inadequate or unnecessary treatment. Image artefacts can be minimized by gating the image acquisition according to respiratory phase and cardiac contractions. However, currently there are no clinically established dual-gating methods in nuclear medicine imaging. The aim of this study is to validate a previously determined optimized bioimpedance measurement configuration against traditional respiratory and cardiac measurement systems in 12 volunteers. High agreement and excellent correlations (r = 0.944-0.999) were found between respiratory peak-to-peak amplitudes as well as temporal respiratory and cardiac intervals. Above all, good quality respiratory and cardiac gating signals were obtained from all test subjects with a fairly regular sinus rhythm. Importantly, both signals were acquired simultaneously with a single device. Due to the simplicity of this inexpensive method, the technique has high potential to be adopted for dual-gating in clinical practice in the future.

Summary Aim: Reversible or irreversible myocardial damage due to ischemia correlates with altered membrane functions of the cells. To compare myocardial free fatty acid (FFA) metabolism and flow during exercise induced ischemia we studied ten patients with coronary artery disease but without previous myocardial infarction. Methods: A series of post-exercise single-photon emission computed tomography (SPECT) measurements was performed after injection of 123I labelled heptadecanoic acid (HDA). Myocardial perfusion was estimated from the separately performed exercise-redistribution thallium study. Fatty acid metabolic rate, thallium uptake and washout were calculated for anterior, lateral, posterior and septal segments. Results: The more reduced post-exercise FFA metabolic rate (–63 ±18%, mean ±1 SD) compared to flow (–36 ±16%) was related to the severity of myocardial ischemia and wall motion abnormalities. Conclusion: In this small group of patients, the reduced post-exercise FFA metabolic rate tentatively suggests a parsimonious workload of the exercising myocardium by reducing oxygen consumption in patients with coronary artery disease.

The aim of the study was to evaluate quality of myocardial perfusion single-photon emission tomography (SPET) imaging in Finnish hospitals. Nineteen nuclear medicine departments participated in the study. A myocardial phantom simulating clinical stress and rest conditions was filled with routinely used isotope solution (technetium-99m or thallium-201). The cardiac insert included three reversible defects (simulating ischaemia): 30x30x14 mm(3) septal (90% recovery at rest), 30x20x14 mm(3) posterobasal (full recovery) and 20x20x14 mm(3) lateral (full recovery). There were two fixed defects (simulating infarct): 30x20x14 mm(3) postero-apical and 10x10x6 mm(3) apical. The phantom was imaged and interpreted as a myocardial perfusion patient. Reconstruction, printout and reporting were performed according to the clinical routine of each centre. Three nuclear medicine specialists anonymously evaluated the quality of the image sets. The visual scores of the experts were ranked from 1 to 5. Additionally, points from 0 to 8 were given to research reports according to how well perfusion defects were detected. Quantitative points were calculated by comparing background-subtracted and -normalized counts from 12 regions of interest between stress and rest images. Results for technetium studies (12 departments) were better than those for thallium (7 departments). The average visual scores of the experts were 3.7+/-0. 9 for all image sets, 3.2+/-0.5 for thallium users and 3.9+/-0.6 for technetium users (P=0.003). Five laboratories received a low score which, according to the specialists, is barely sufficient for limited clinical use. Average points for the reports were 5.6+/-2.1, 4.9+/-1.5 and 6.5+/-1.7 (P=0.051), and for the quantitation 8.2+/-1. 0, 7.9+/-0.4 and 8.4+/-1.1 (P=0.185), respectively. Seven out of 22 interpreters did not detect the lateral 20x20x14 mm(3) defect; five of them used thallium. This study demonstrated the heterogeneity of myocardial perfusion SPET in Finland. The participating laboratories used a wide scale of methods and, sometimes, inappropriate imaging protocols. The need for quality assurance in nuclear cardiology, correct use of SPET instrumentation and objective comparison of clinical studies is evident. The method described is suitable for external quality assurance and quality improvement of myocardial SPET imaging, and is recommended for regular use in nuclear medicine.

In myocardial perfusion SPET studies with 99 Tc m -Q12, we observed that some patients had high liver uptake that interfered significantly in the assessment of the inferior wall. The aim of this study was to assess the effects of the radiochemical purity of 99 Tc m -Q12 on liver uptake. Thirty-one patients undergoing routine myocardial infarction perfusion studies were evaluated. The radiochemical purity of 99 Tc m -Q12 was determined using HPLC. Venous blood samples taken 50 min after injection of 99 Tc m -Q12 during peak exercise were also analysed. Liver uptake was expressed as the liver-to-heart ratio. In addition, the SPET images were classified by two experienced nuclear medicine specialists into three groups representing high-quality images (n = 7), images with high general background activity (n = 13) and images with high liver and/or intestinal uptake (n = 11). The liver-to-heart ratio correlated inversely with the radiochemical purity of 99 Tc m -Q12 (r = -0.65, P < 0.001) and unchanged 99 Tc m -Q12 in plasma (r = -0.44, P < 0.02). The radiochemical purity of 99 Tc m -Q12 was significantly lower in the group with high liver uptake (60.1 ± 4.2%) than in the group with good-quality images (81.8 ± 5.6%, P < 0.01) or with high background activity (82.3 ± 2.5%, P < 0.01). In conclusion, the radiochemical purity of 99 Tc m -Q12 has a significant inverse correlation with the liver-to-heart ratio; thus, the high radiochemical purity of 99 Tc m -Q12 should be confirmed to prevent interference by liver uptake.

Rationale: There are no previous data available regarding [123I]β-CIT binding to the dopamine transporter sites in the basal ganglia in depressed patients. Objective: The present study tested the hypothesis that the brain DAT density in depressed patients is lower than that in matched healthy controls. Methods: Fifteen drug-naive outpatients with major depression and 18 healthy controls were investigated using single photon emission computerized tomography (SPECT) with a high-affinity dopamine transporter specific radioligand, 123I-labeled β-CIT (2β-carbomethoxy-3β-(4-iodophenyl)-tropane). Results: We found a significantly higher [123I]β-CIT uptake in both sides of the basal ganglia in patients with major depression than in the controls (Mann-Whitney U-test, P = 0.002 on the right and P = 0.003 on the left). Conclusions: The radioligand uptake reflecting the DAT density was significantly higher among the patients than in the controls. This finding is unexpected, since it is generally believed that monoaminergic neurotransmission is lower in depression, and therefore it could be assumed that a reduction in dopamine transmission would lead to secondary down-regulation of DAT density. However, it is possible that up-regulation of the DAT may be the primary alteration, which leads to lower intrasynaptic dopamine concentration and to lower dopamine neural transmission.

SummaryPhoton scatter is one of the most important factors degrading the quantitative accuracy of SPECT images. Many scatter correction methods have been proposed. The single isotope method was proposed by us. Aim: We evaluate the scatter correction method of improving the quality of images by acquiring emission and transmission data simultaneously with single isotope scan. Method: To evaluate the proposed scatter correction method, a contrast and linearity phantom was studied. Four female patients with fibromyalgia (FM) syndrome and four with chronic back pain (BP) were imaged. Grey-to-cerebellum (G/C) and grey-to-white matter (G/W) ratios were determined by one skilled operator for 12 regions of interest (ROIs) in each subject. Results: The linearity of activity response was improved after the scatter correction (r = 0.999). The y-intercept value of the regression line was 0.036 (p

Knowledge of the contributions of transit time heterogeneity to the cardiopulmonary system is important for understanding cardiopulmonary function in patients with intracardiac shunt. We determined the heterogeneity of blood transit times occurring between the right atrium and the left ventricle. Eighty two patients with suspected left-to right shunt were investigated with first-pass 99mTc-labelled red blood cell radiocardiography at supine rest. Forty two of them had a pulmonary-to-systemic flow ratio (Qp:Qs) of less than 1.2 and they served as a control group. The remaining study subjects had a Qp:Qs ratio of 1.7 +/- 0.3 (mean +/- SD). The patients with shunt had significantly greater (p0.001) heterogeneity of transit times (49 +/- 9%) than in the controls (39 +/- 7%). Overall heterogeneity of cardiopulmonary transit times in patients with shunt showed a curvature relationship; the highest values were centred in patients with moderate to severe shunt (1.5Qp:Qs2.5). The results suggest that the increased heterogeneity of transit times mainly occurs within the pulmonary capillary bed in patients with intracardiac shunt. This is probably due to the recruitment of the open capillaries without vessel distension.

We evaluated the physical performance of the new Siemens E.CAM gamma camera. The camera is a dual-headed, large detector system with an open gantry dedicated to planar and to multislice single photon emission tomographic (SPET) imaging of the whole body. The energy-independent digital detectors with high-quality photo-multiplier tubes seem to keep the physical performance of the E.CAM camera very stable. The imaging resolution is very good. The SPET resolution is 9.1 mm full-width at half maximum in scatter for high-resolution collimators with a rotational radius of 15 cm. Both planar (or = 2%) and SPET uniformity (or = 4%) are excellent. The detectors can be configured at variable angles which allows flexibility, especially in heart studies. Autocontouring performs whole-body and SPET scans as close to the patient as possible. The patient couch, with its very low gamma-ray attenuation, is firm and can be lowered to make patient loading easier. Camera tuning, calibration, acquisition and processing are controlled by two Power Macintosh 8500 computers. The ICON software is easy to use (a mouse-driven system). However, acquisition interrupts and autocontouring errors were noted during our initial experience. The image quality of routine bone and heart scans was excellent. The E.CAM system allows fast and accurate planar and SPET imaging both in clinical practice and research.

This review article forecasts developments in nuclear medicine instrumentation which are on the horizon. Special attention is paid to the physical properties of detectors and multiple-processor parallel processing systems needed for fast and high-quality imaging in emission tomography. Advances in detector technology will improve imaging resolution below 5 mm and will increase sensitivity and quantitative accuracy. In addition, high count rate list-mode acquisition enables 'true' four-dimensional data-sets. A sandwich-like construction of two different crystals allows the simultaneous use of conventional tracers and positron tracers (multiple emission tomography, MET). Transmission-based attenuation and scatter compensation with fast iterative reconstruction methods will further improve image quality. The clinical and scientific importance of improved images and the limits on advances in instrumentation are also reviewed.

Epidemiological studies have suggested that patients with rheumatoid arthritis (RA) have increased mortality due to cardiovascular disease. We studied cardiac performance in 12 asymptomatic male patients with RA and 14 control subjects to elucidate early disturbances in cardiac function. In echocardiography, isovolumic relaxation time was longer (64 +/- 6 vs. 49 +/- 3 ms, mean +/- SEM, P = 0.010) and peak filling rate (134 +/- 10 vs. 159 +/- 6 mm s-1, P = 0.015) lower in patients with RA than in control subjects, reflecting an impairment in left ventricular diastolic function. Left ventricular systolic function assessed by radionuclide angiocardiography at rest and during exercise was similar in both groups. There were no differences between the patients with RA and control subjects in the heart rate, systolic blood pressure and oxygen uptake during peak exercise. Left ventricular diastolic function is impaired in spite of normal left ventricular systolic function in patients with RA without clinically evident cardiovascular disease and this may contribute to the excess of cardiovascular mortality in patients with RA.

To evaluate apparent diffusion coefficient (ADC) in cerebellar subregions in patients with stroke.The total counts and ADCs were bilaterally measured on cerebellar white matter, gray matters of medial (G1), intermediate (G2), and lateral zones (G3) on SPECT and ADC maps from 20 patients with supratentorial ischemic stroke within the first 48 h and on day 8 after onset. ADCs were also obtained from 15 age-matched controls.Within 48 h, the ADCs were significantly increased bilaterally in the G3, and tended to be increased bilaterally in the white matter and G1, and contralateral G2 compared with controls. On day 8, the ADCs were significantly increased in all contralateral cerebellar subregions and in ipsilateral G1 and G2, and tended to be increased in ipsilateral G3. The ADC value was significantly higher in contralateral than in ipsilateral white matter on day 8. The interhemispheric asymmetry indices (AIs) of ADC and SPECT were significantly associated with each other in G2 and G3 within 48 h, but not on day 8. The AIs of ADC and SPECT were significantly related to each other in the G3 within 48 h and on day 8.Supratentorial ischemic stroke may cause mild cerebellar vasogenic edema.

Alterations in dopaminergic and serotonergic systems have been observed in many neuropsychiatric disorders. We evaluated the reproducibility of dopamine (DAT) and serotonin transporter (SERT) binding measured with single-photon emission computed tomography (SPECT). Two repeated SPECT studies with nor-(β-CIT were performed within one year interval in 11 healthy control subjects. The intraclass correlation coefficient was 0.79 (p < 0.01) for DAT and 0.82 (p < 0.01) for SERT, respectively. The agreements between two measurements were good. Therefore we considered acceptable to use SPECT with nor-(β-CIT in measurements of DAT and SERT binding in various neuropsychiatric disorders.

The iodine-123 labelled selective ligand N-(3-iodoprop-2E-enyl)-2beta-carbomethoxy-3beta-(4-methylphe nyl)nortr opane ([(123)I]PE2I) has been developed and has been shown to be suitable for single-photon emission tomography imaging of the dopamine transporter. In this study the influence of age on ligand binding was investigated in 16 healthy males with an age range of 23- 75 years. Single-photon emission tomography (SPET) imaging was performed with a triple-headed gamma camera. A simplified reference region model, in which the input function was derived from the non-displaceable cerebellar compartment, was used to calculate the volume of distribution in the striatum. The volume of distribution was shown to decline with age (-0.4%/year; P0.005). The results were in agreement with in vivo and in vitro findings of a decline in dopamine transporter binding with age. The findings confirm the suitability of [(123)I]PE2I for SPET imaging in clinical routine but emphasize the necessity of using age-matched controls in patient studies.

Serotonin transporter (SERT) imaging can be used to study the role of regional abnormalities of neurotransmitter release in various mental disorders and to study the mechanism of action of therapeutic drugs or drugs' abuse. We examine the quantitative accuracy and reproducibility that can be achieved with high-resolution SPECT of serotonergic neurotransmission.Binding potential (BP) of (123)I labeled tracer specific for midbrain SERT was assessed in 20 healthy persons. The effects of scatter, attenuation, partial volume, misregistration and statistical noise were estimated using phantom and human studies.Without any correction, BP was underestimated by 73%. The partial volume error was the major component in this underestimation whereas the most critical error for the reproducibility was misplacement of region of interest (ROI).The proper ROI registration, the use of the multiple head gamma camera with transmission based scatter correction introduce more relevant results. However, due to the small dimensions of the midbrain SERT structures and poor spatial resolution of SPECT, the improvement without the partial volume correction is not great enough to restore the estimate of BP to that of the true one.

Interest in clinical fluorodeoxyglucose (FDG) imaging with multiple-head gamma cameras is growing. To improve sensitivity, triple-head coincidence imaging has been proposed. We report our initial experiences with a triple-head coincidence gamma camera with 19 mm sodium iodide crystal thickness. Several positron emission tomography-image quality parameters were evaluated using a Carlson and line source phantom. The system sensitivity with two-dimensional axial shields was 830 cps kBq-1 ml-1 and maximum noise equivalent count rate 1900 cps for an 18F-activity of 50 MBq. The imaging resolution was in central axial 7.0 mm and in central transaxial 7.6 mm, respectively. The average scatter fraction in scattered media was 29%. Clinical brain, heart and whole body images studies with [18F]FDG were acquired and they show good correlation with the phantom image quality. As a conclusion, triple-head coincidence gamma camera provides relatively high-count rate imaging with good contrast and resolution.

Reversible or irreversible myocardial damage due to ischemia correlates with altered membrane functions of the cells. To compare myocardial free fatty acid (FFA) metabolism and flow during exercise induced ischemia we studied ten patients with coronary artery disease but without previous myocardial infarction.A series of post-exercise single-photon emission computed tomography (SPECT) measurements was performed after injection of 123I labelled heptadecanoic acid (HDA). Myocardial perfusion was estimated from the separately performed exercise-redistribution thallium study. Fatty acid metabolic rate, thallium uptake and washout were calculated for anterior, lateral, posterior and septal segments.The more reduced post-exercise FFA metabolic rate (-63 +/- 18%, mean +/- 1 SD) compared to flow (-36 +/- 16%) was related to the severity of myocardial ischemia and wall motion abnormalities.In this small group of patients, the reduced post-exercise FFA metabolic rate tentatively suggests a parsimonious workload of the exercising myocardium by reducing oxygen consumption in patients with coronary artery disease.

In non-ischaemic myocardium glucose uptake is assumed to be proportional to blood flow. We investigated the effect of regional vascular heterogeneity on glucose metabolism at various flow rates in the isolated blood-perfused dog hearts. Aortic bolus injections contained an intravascular reference tracer (albumin) and two of three glucoses: L-glucose (an extracellular tracer), D-glucose and 2-deoxy-D-glucose. Flow ranged from 0.5 to 2 4 ml min(-1) g(-1). Vascular heterogeneity was calculated from the albumin outflow dilution curve. A three-region convection-diffusion from the abumin outflow dilution curve. A three-region, convection-diffusion model was fitted to outflow dilution curves to estimate glucose metabolic rate (consumption). The results of 2-deoxy-D-glucose experiments showed that the lumped constant was dependent on flow, glucose metabolic rate was proportional to flow and dependent on the heterogeneity of the myocardial vasculature. The results support the views that without accounting the regional flow heterogeneity, glucose metabolic rate will be underestimated.

Existing methods to determine the binding potential in brain receptor and transporter studies with single-photon emission computed tomography (SPECT) show a marked dependence on the physical performance of the scanner and on the regions of interest (ROIs) drawn. We examined the influence of the physical performance on the binding potential.The authors tested three gamma cameras (single-, dual- and triple-head) and two reconstruction techniques (conventional filtered back-projection and iterative reconstruction method) to determine the binding potential in brain receptor studies. Both human and organ-like phantom studies were performed.The binding potential was completely dependent on the imaging resolution, on the reconstruction technique used and on the ROIs drawn. The results of the phantom study revealed that the striatum-to-cerebellum ratio was only 37% of the actual one for the single-head, 63% for the dual-head and 72% for the triple-head gamma camera.The multiple head gamma camera with fan-beam collimators and iterative reconstruction with the attenuation based scatter correction is an imaging system of choice which introduces clinically more relevant images and is able to distinguish smaller differences in radioactivity at early stage of disease. However, for quantitative purposes the improvement without the use of the recovery coefficient is not great enough to restore the binding potentials to those of the true ones.

In acute ischemic stroke, the infarcted core is surrounded by a zone of tissue that has decreased perfusion. Some of this tissue may be salvaged by prompt, effective treatment. Diffusion-weighted MRI is sensitive in detecting the infarcted tissue, whereas SPECT also detects the hypoperfused tissue around the infarcted core. We studied the potential of combined diffusion-weighted MRI and SPECT to predict infarct growth and clinical outcome in patients not receiving thrombolytic treatment.Sixteen patients with acute stroke were examined consecutively with diffusion-weighted MRI and 99mTc-ethyl cysteinate dimer (99mTc-ECD) SPECT within 24 h of the onset of symptoms. Follow-up diffusion-weighted MRI was performed on the second day and after 1 wk. The volumes of infarcted and hypoperfused brain tissue were measured from diffusion-weighted MRI and SPECT, respectively. The volume difference between the hypoperfused and infarcted tissue on the first day was compared with the possible increase in infarct volume during the follow-up. Each patient's neurologic status was assessed with the National Institutes of Health Stroke Scale (NIHSS).The volume of infarcted tissue increased from 48 +/- 54 cm3 (mean +/- SD) on the first day to 88 +/- 93 cm3 on the second day (P = 0.001) and to 110 +/- 121 cm3 at 1 wk (P = 0.001). The volume of hypoperfused tissue on the first day was significantly greater than the infarct volume (102 +/- 135 cm3; P = 0.001). The volume difference between the hypoperfused and infarcted tissue on the first day correlated significantly with the infarct growth between the first day and 1 wk (r = 0.71; P0.01). Between the first day and 1 wk, the increase of the infarct volume correlated significantly with the change in the NIHSS (r = 0.54; P0.05).A large hypoperfusion zone around the infarct core in the acute phase of ischemic stroke predicts the infarct growth during the first week, and this correlates significantly with the change in the neurologic status of the patient. Combined diffusion-weighted MRI and SPECT performed within 24 h after the onset of symptoms can be useful in the evaluation of acute stroke to predict infarct growth.

We demonstrate the heterogeneity of regional cerebral blood flow using a fractal approach and single-photon emission computed tomography (SPECT).Tc-99m-labelled ethylcysteine dimer was injected intravenously in 10 healthy controls and in 10 patients with dementia of frontal lobe type. The head was imaged with a gamma camera and transaxial, sagittal and coronal slices were reconstructed. Two hundred fifty-six symmetrical regions of interest (ROIs) were drawn onto each hemisphere of functioning brain matter. Fractal analysis was used to examine the spatial heterogeneity of blood flow as a function of the number of ROIs.Relative dispersion (= coefficient of variation of the regional flows) was fractal-like in healthy subjects and could be characterized by a fractal dimension of 1.17 +/- 0.05 (mean +/- SD) for the left hemisphere and 1.15 +/- 0.04 for the right hemisphere, respectively. The fractal dimension of 1.0 reflects completely homogeneous blood flow and 1.5 indicates a random blood flow distribution. Patients with dementia of frontal lobe type had a significantly lower fractal dimension of 1.04 +/- 0.03 than in healthy controls.Within the limits of spatial resolution of SPECT, the heterogeneity of brain blood flow is well characterized by a fractal dimension. Fractal analysis may help brain scientists to assess age-, sex- and laterality-related anatomic and physiological changes of brain blood flow and possibly to improve precision of diagnostic information available for patient care.

To study its usefulness as a tracer for assessment of the perfusion and viability of myocardium, 15-(p-iodophenyl)pentadecanoic acid (IPPA) was compared with technetium-99m sestamibi (MIBI). Dual-tracer single-photon emission tomography rest imaging was performed no more than 2 months before and 3 months after coronary artery bypass grafting in 28 patients with previous anterior (n=13) or inferior (n=15) infarction. The size of MIBI and IPPA defects decreased from 14%+/-12% and 13%+/-9% to 10%+/-11% and 9%+/-7%, respectively (P0.001 for both). The MIBI uptake increased in the infarct zones from 35%+/-11% to 43%+/-8% (P0.001), and in the peri-infarct zones from 50%+/-11% to 55%+/-10% (P0.05). The IPPA uptake increased in the infarct zones from 37%+/-11% to 44%+/-13% (P0.001), and in the peri-infarct zones from 51%+/-11% to 57%+/-12% (P0.05). In nine patients with improved regional echocardiographic wall motion score after bypass surgery, the pre-operative uptake values of both MIBI and IPPA in the infarct and peri-infarct zones were on average slightly but not significantly higher than in 19 patients with no observed improvement in regional wall motion score. In patients with improved regional wall motion, the MIBI scans and the IPPA scans showed (non-significant) decreases in defect size and increases in infarct and peri-infarct zone uptake after bypass surgery. Similar (in some cases significant) changes were observed in the patients without improvement in wall motion. Thus IPPA and MIBI provided similar information about perfusion and viability in pre- and postoperative evaluation of patients with clinically evident myocardial infarction and with normal global ejection fraction. Regardless of the tracer used, the resolution capability of the dual-tracer method with a rest imaging protocol was not sufficient to differentiate viable from non-viable infarction defects in unselected individual patients with a normal ejection fraction.

Background and Purpose —More effective imaging methods are needed to overcome the limitations of CT in the investigation of treatments for acute ischemic stroke. Diffusion-weighted MRI (DWI) is sensitive in detecting infarcted brain tissue, whereas perfusion-weighted MRI (PWI) can detect brain perfusion in the same imaging session. Combining these methods may help in identifying the ischemic penumbra, which is an important concept in the hemodynamics of acute stroke. The purpose of this study was to determine whether combined DWI and PWI in acute ( Methods —Forty-six patients with acute ischemic stroke underwent DWI and PWI on days 1, 2, and 8. No patient received thrombolysis. Twenty-three patients underwent single-photon emission CT in the acute phase. Lesion volumes were measured from DWI, SPECT, and maps of relative cerebral blood flow calculated from PWI. Results —The mean volume of infarcted tissue detected by DWI increased from 46.1 to 75.6 cm 3 between days 1 and 2 ( P 3 after 1 week ( P r =0.699, P r =0.827, P r =0.824, P Conclusions —Combined DWI and PWI can predict infarct enlargement in acute stroke. PWI can detect hypoperfused brain tissue in good agreement with SPECT in acute stroke.

Changes in pulmonary circulation caused by muscular exercise and body position are usual in daily life. By using first-pass radiocardiography and fractal analysis, pulmonary circulation in man was evaluated at rest and during muscular exercise. At rest, pulmonary circulation was heterogeneous as described by the relative dispersion (which is the coefficient of variation, i.e. the standard deviation of the pulmonary transit times divided by the mean transit time; RD = 0.51 +/- 0.06) and fractal in nature. During exercise, pulmonary circulation became more homogeneous (RD = 0.35 +/- 0.04; P0.001). The calculated fractal dimension decreases from 1.09 at rest to 1.06 during exercise. The model identifies a cubic-law response for circulation heterogeneity and a quarter-power law for resistance during muscular exercise.

Photon scatter is one of the most important factors degrading the quantitative accuracy of SPECT images. Many scatter correction methods have been proposed. The single isotope method was proposed by us.We evaluate the scatter correction method of improving the quality of images by acquiring emission and transmission data simultaneously with single isotope scan.To evaluate the proposed scatter correction method, a contrast and linearity phantom was studied. Four female patients with fibromyalgia (FM) syndrome and four with chronic back pain (BP) were imaged. Grey-to-cerebellum (G/C) and grey-to-white matter (G/W) ratios were determined by one skilled operator for 12 regions of interest (ROIs) in each subject.The linearity of activity response was improved after the scatter correction (r = 0.999). The y-intercept value of the regression line was 0.036 (p0.0001) after scatter correction and the slope was 0.954. Pairwise correlation indicated the agreement between nonscatter corrected and scatter corrected images. Reconstructed slices before and after scatter connection demonstrate a good correlation in the quantitative accuracy of radionuclide concentration. G/C values have significant correlation coefficients between original and corrected data.The transaxial images of human brain studies show that the scatter correction using single isotope in simultaneous transmission and emission tomography provides a good scatter compensation. The contrasts were increased on all 12 ROIs. The scatter compensation enhanced details of physiological lesions.

Evidence from animal studies suggest that centrally acting opiates increase synaptic dopamine (DA) concentration. However, the interaction between mu-opioid receptors and the DA system is unclear. We report here an effect of fentanyl on striatal [123I]beta-CIT binding to the DA transporter in a patient and in rats. A female patient underwent [123I]beta-CIT single-photon emission tomography (SPET) study after intrathecal injection of fentanyl for her back pain. After a 2-week drug-free period, the SPET study was repeated. In the experimental study, male Wistar rats were treated with fentanyl either acutely (50 micrograms/kg, i.p.) before imaging study or subacutely for 4 days (10 micrograms/kg, twice a day, i.p.). Brain planar imaging was performed at 3.5 hours after an intravenous injection of [123I]beta-CIT with gamma camera with a pinhole collimator. In a female patient, [123I]beta-CIT binding in the basal ganglia was decreased by 37% during fentanyl as compared to the binding after 2-week drug-free period. Similarly in rats, acute fentanyl treatment decreased [123I]beta-CIT binding to the striatum by 30% as compared to that of with the control rats. After subacute administration of fentanyl, no significant difference was observed compared to the control group. According to the present data, fentanyl decreases [123I]beta-CIT binding in the basal ganglia both in human and rats, suggesting that opiates possibly directly affect DA reuptake.

Six healthy controls and 13 patients with Parkinson’s disease in different disability stages were studied with high resolution SPET using [123I]β-CIT-FP. The caudatus­to-cerebellum and putamen-to-cerebellum ratios were calculated at 3.5 hours after injection. Patients had the significantly lower ratio than that of the controls in the putamen (3.0 ± 1.0 vs. 4.7 ± 0.4 ) and in the caudatus (3.5 ± 1.1 vs. 4.9 ± 0.5), respectively. There was a significant negative correlation between the ratio and the Hoehn and Yahr stage in the putamen (r = −0.74) and in the caudatus(r = −0.80). Reduced striatal uptake demonstrates the loss of presynaptic nerve endings in the striatum of the patients with Parkinson’s disease.

I-123 or C-11 labelled 2 beta-carbomethoxy-3 beta-(4-iodophenyl)tropane (beta-CIT) is a recently developed radioligand for the study of dopamine and serotonin reuptake sites in humans with single photon emission tomography (SPET) or positron emission tomography (PET). Determination of the radioligand metabolite pattern is fundamental for a quantitative analysis of radioligand binding. The metabolism of [123I]beta-CIT was determined by a gradient HPLC method in plasma samples of six human subjects. Two metabolites of [123I]beta-CIT were found, a polar and a lipophilic. At 4 h after [123I]beta-CIT injection the percentages of parent compound and polar and lipophilic metabolites were 23 +/- 3% (mean +/- SD), 33 +/- 11%, and 44 +/- 8%, respectively. The lipophilic metabolite might pass the blood-brain barrier and account for a fraction of free and nonspecifically bound radioactivity in brain. The existence of a lipophilic metabolite of [123I]beta-CIT may obstruct the use of simple ratio methods for quantitation of the dopamine transporter in brain.

beta-CIT (2 beta-carbomethoxy-3 beta-(4-iodophenyl)tropane) is a new ligand that has a high affinity to dopamine and serotonin re-uptake sites. [123I] beta-CIT was prepared by reacting the corresponding trimethylstannyl precursor with no-carrier-added 123I. Iodogen was used as an oxidizing agent. The labeling mixture was purified by filtration through a mini-column. The purity of the product was confirmed by analytical HPLC. The total radiochemical yield was 67 +/- 5%. The radiochemical purity was95% and the specific activity was107 GBq/mol (2900 Ci/mmol). The final product was confirmed to be free of endotoxins before intravenous administration. Two healthy male volunteers were injected iv with 120-160 MBq of [123I] beta-CIT and scanned with a 3-head gamma-camera (Siemens MultiSPECT3). Dynamic SPECT scans were performed for up to 2 hours. There was a high accumulation of radioactivity in the striatum and in the thalamus, and some in the medial prefrontal area. Thus, we have developed an easy method to prepare [123I] beta-CIT with a high specific radioactivity and in a sufficient radiochemical yield. Specific [123I] beta-CIT binding in striatal and thalamic regions was demonstrated in humans. [123I] beta-CIT is a potential marker of the dopamine and serotonin transporters and can be used to study the pathophysiology of Parkinson's disease, as well as neuropsychiatric disorders.

This report documents the radiation dosimetry of iodine-123 labelled 2 beta-carbomethoxy-3 beta-(4-iodophenyl)tropane [123I]beta-CIT in humans. The mean absorbed doses for various organs and the effective dose equivalent were estimated from whole-body scans, blood samples and single-photon emission tomography scans acquired up to 22 h after the injection of a known amount of tracer. The basal ganglia, the liver and the lower large intestinal wall received the highest mean absorbed doses of 0.270 mGy/MBq, 0.038 mGy/MBq and 0.034 mGy/MBq, respectively. The effective dose equivalent for adults was estimated using 11 organs and the ICRP-87 radiation dose model and was 0.031 mSv/MBq. The radiation dose to the basal ganglia limits the maximum injected activity of [125I]beta-CIT to 185 MBq for a single study.

The myocardial uptake of glucose and fatty acids into 201Tl redistribution defects were studied in 32 patients with myocardial infarction by tomography using 2-18F-2-deoxyglucose (FDG) and 15-(ortho-123I-phenyl)-pentadecanoic acid (oPPA). A total of 1153 segments were analyzed, 408 (35%) of which showed a persistent thallium-defect in stress-redistribution images. Of the segments with a decreased 201Tl uptake in these redistribution tomograms, 50.5% had a decreased uptake of both FDG and oPPA; in 21.8% FDG as well as oPPA uptake was within normal range. Normal FDG uptake but decreased oPPA uptake was detected in 17.4%, whereas 10.3% of the segments had normal oPPA uptake but decreased FDG uptake (chi-square test, p less than 0.001). A significant correlation of FDG and oPPA uptake (r = 0.51) was found in the segments with persistent 201Tl defect. Thus, a substantial fraction of persistent thallium-defects after healed myocardial infarction exhibit FDG as well as oPPA uptake, probably due to residual fatty acid metabolism in partially ischemic regions.

SPECT studies with L-3-[123I]iodo-alpha-methyl tyrosine (IMT) were carried out in 10 patients with different types of brain tumors--first under fasting conditions (basal) and a week later during intravenous infusion of a mixture of naturally-occurring L-amino acids (AA load). An uptake index (UI) was calculated by dividing tissue count rates by the integral of plasma count rates. The UI decreased by 45.6% +/- 15.4% (n = 10, p less than 0.001) for normal brain and by 53.2% +/- 14.1% for gliomas (n = 5, p less than 0.01) during AA load compared to basal conditions, while two meningiomas and a metastasis showed only a minor decrease (23.9 +/- 5.7%, n.s.). Two pituitary adenomas could not be delineated on the SPECT scans. These data indicate that IMT competes with naturally-occurring L-amino acids for transport into normal brain and gliomas. Transport characteristics of IMT into tumors of nonglial origin appear to be different from those of gliomas. For both types of tumors, it is advisable to perform IMT-SPECT under fasting conditions.

The purpose of this paper is to review different models used in the interpretation of capillary permeability studies using tracer dilution methods, with special emphasis on the role of cyclotron-produced isotopes. The physical model is a simplified description of the biological system, and the mathematical formalism is a device by which the model and experimental data can be compared. If there is a correlation and the solution is unique and consistent, the model is considered acceptable. Capillaries--the end organs of the circulatory system--are physiologically important because they are the site for the exchange of materials (oxygen, glucose, waste products etc.). The positive and negative findings in radionuclide imaging studies are caused by changes in capillary permeability. The indicator diffusion methods have many advantages over the conventional compartmental analyses. The diffusion models take into account the normal histological structure of the tissue and it is possible to get information about both capillary and cellular physiology. Short-lived, cyclotron produced positron emitting radionuclides, carbon-11, nitrogen-13, oxygen-15 and fluorine-18, are suitable for the study of transcapillary exchange.

The objectives of this study were to measure in vivo an instantaneous partition coefficient of xenon, and to estimate the effect of it on calculated flow values obtained from washout experiments. The results suggest that the calculated xenon clearance based on the static equilibrium partition coefficient is not exactly the actual flow, but rather a mathematical flow index, which is highly dependent on flow and diffusion rates.