A method to determine the coverage of ivermectin distribution in onchocerciasis-control programmes

AIM: To study the refractive status and corneal topography in Down's syndrome. METHOD: A matched cohort subgroup of 50 individuals with Down's syndrome in the Manchester area aged 15-22 years was studied by refraction, corneal topography, A-scan biometry, slit lamp examination, and orthoptic examination. RESULTS: (1) A linear relation was found between axial length and spherical equivalent refraction. There was no statistical relation between keratometry and the axial length. (2) 80% of the group had a hyperopic refraction (mean +2.46 D, range +0.5 to +7.5 D); 18% were myopic (mean -2.75 D, range -0.5 to -8.0 D); and 2% were emmetropic (within plus or minus 0.5 D of zero). The overall mean spherical equivalent refraction was +1.43 (SD 2.86) D. 63% of eyes could see 6/12 or better and 66% of the individuals had a binocular vision of 6/12 or better. (3) Corneal topography was generally of a regular "bow tie" pattern, but there was a high incidence of oblique cylinders. Mean cylinder strength was 1.14 (1.15) D. (4) The prevalence of overt keratoconus was 2%. 6% had corneal topography with inferior steepening which may be a preclinical keratoconic process. CONCLUSIONS: In this cohort of late teenagers with Down's syndrome, emmetropisation has failed to occur in most individuals. In a similar aged group of non-disabled individuals one would expect about 83% emmetropic (plus or minus 0.25 D), 13% myopic, and 4% hyperopic. The wide spread of oblique cylinders and the small proportion of with the rule astigmatism is probably related to this failure of emmetropisation. The prevalence of 2% keratoconus in Down's syndrome compares with that found by other authors of between 5.5 and 15%. The 6% with inferior steepening on topography will be followed up over the next few years to see if there is any development of clinical keratoconus. Hence we will see if corneal topography is useful as a screening tool for preclinical keratoconus in this high risk group.     

Limits to milk flow and energy allocation during lactation of the hispid cotton rat (Sigmodon hispidus)

INTRODUCTION: Epicardial and endocardial defibrillation electrode systems affect myocardial electrophysiology and sympathetic function differently. Thus, we postulate that antiarrhythmic drugs will interact with these electrode systems differently. METHODS AND RESULTS: Defibrillation energy requirements (DER) at 20% (ED20), 50% (ED50), and 80% (ED80) success were measured at baseline and during lidocaine (10 mg/kg per hour) or D5W treatment for epicardial and endocardial electrodes. Pigs were randomized to treatment (lidocaine or D5W) and electrode system, which resulted in four experimental groups: (1) epicardial electrode + D5W; (2) epicardial electrode + lidocaine; (3) endocardial electrode + D5W; and (4) endocardial electrode + lidocaine. ED50 DER (mean +/- SEM) values at baseline for groups 1-4 were 10.6+/-1, 8.5+/-1, 12.6+/-1, and 12.3+/-1 J, respectively. DER values for groups 1 and 3 during D5W were similar to baseline. Conversely, lidocaine increased ED50 DER values from 8.5+/-1 to 13.5+/-2 J (P < 0.05) in group 2 animals (epicardial electrodes). When lidocaine was administered to group 4 animals (endocardial electrodes), however, ED50 DER values remained similar to baseline values (12.3+/-1 to 14.3+/-2 J, P = NS). Lidocaine increased ED50 DER values by 59% with the epicardial electrode system, which was significantly greater than the 16% increase with the endocardial electrode system (P < 0.05). Electrophysiologic response and electrode impedance were similar between electrode systems. CONCLUSION: Lidocaine increases DER values to a greater extent when using epicardial versus endocardial electrode system. Thus, drug-device interactions are dependent on the electrode system. These data suggest that the electrophysiologic milieu created by endocardial defibrillation mitigates the effects that lidocaine has on DER values.     

Psychiatric disorder onset and first treatment contact in the United States and Ontario

The aim of the study was to evaluate the quality of routine brain perfusion single-photon emission tomography (SPET) images in Finnish nuclear medicine laboratories. Twelve laboratories participated in the study. A three-dimensional high resolution brain phantom (Data Spectrum's 3D Hoffman Brain Phantom) was filled with a well-mixed solution of technetium-99m (110 MBq), water and detergent. Acquisition, reconstruction and printing were performed according to the clinical routine in each centre. Three nuclear medicine specialists blindly evaluated all image sets. The results were ranked from 1 to 5 (poor quality-high quality). Also a SPET performance phantom (Nuclear Associates' PET/SPECT Performance Phantom PS 101) was filled with the same radioactivity concentration as the brain phantom. The parameters for the acquisition, the reconstruction and the printing were exactly the same as with the brain phantom. The number of detected "hot" (from 0 to 8) and "cold" lesions (from 0 to 7) was visually evaluated from hard copies. Resolution and contrast were quantified from digital images. Average score for brain phantom images was 2.7 +/- 0.8 (range 1.5-4.5). The average diameter of the "hot" cylinders detected was 16 mm (range 9.2-20.0 mm) and that of the "cold" cylinders detected, 11 mm (5.9-14.3 mm) according to visual evaluation. Quantification of digital images showed that the hard copy was one reason for low-quality images. The quality of the hard copies was good only in four laboratories and was amazingly low in the others when comparing it with the actual structure of the brain phantom. The described quantification method is suitable for optimizing resolution and contrast detectability of hard copies. This study revealed the urgent need for external quality assurance of clinical brain perfusion SPET images.     

Accurate three-dimensional reconstruction of intravascular ultrasound data. Spatially correct three-dimensional reconstructions

BACKGROUND: The geometrical accuracy of conventional three-dimensional (3D) reconstruction methods for intravascular ultrasound (IVUS) data (coronary and peripheral) is hampered by the inability to register spatial image orientation and by respiratory and cardiac motion. The objective of this work was the development of improved IVUS reconstruction techniques. METHODS AND RESULTS: We developed a 3D position registration method that identifies the spatial coordinates of an in situ IVUS catheter by use of simultaneous ECG-gated biplane digital cinefluoroscopy. To minimize distortion, coordinates underwent pincushion correction and were referenced to a standardized calibration cube. Gated IVUS data were acquired digitally, and the spatial locations of the imaging planes were then transformed relative to their respective 3D coordinates, rendered in binary voxel format, resliced, and displayed on an image-processing workstation for off-line analysis. The method was tested by use of phantoms (straight tube, 360 degrees circle, 240 degrees spiral) and an in vitro coronary artery model. In vivo feasibility was assessed in patients who underwent routine interventional coronary procedures accompanied by IVUS evaluation. Actual versus calculated point locations were within 1.0 +/- 0.3 mm of each other (n = 39). Calculated phantom volumes were within 4% of actual volumes. Phantom 3D reconstruction appropriately demonstrated complex morphology. Initial patient evaluation demonstrated method feasibility as well as errors if respiratory and ECG gating were not used. CONCLUSIONS: These preliminary data support the use of this new method of 3D reconstruction of vascular structures with use of combined vascular ultrasound data and simultaneous ECG-gated biplane cinefluoroscopy.     

Interleukin-8 (IL-8) and monocyte chemotactic and activating factor (MCAF/MCP-1), chemokines essentially involved in inflammatory and immune reactions

We analyzed the noise characteristics of two-dimensional (2-D) and three-dimensional (3-D) images obtained from the GE Advance positron emission tomography (PET) scanner. Three phantoms were used: a uniform 20-cm phantom, a 3-D Hoffman brain phantom, and a chest phantom with heart and lung inserts. Using gated acquisition, we acquired 20 statistically equivalent scans of each phantom in 2-D and 3-D modes at several activity levels. From these data, we calculated pixel normalized standard deviations (NSD's), scaled to phantom mean, across the replicate scans, which allowed us to characterize the radial and axial distributions of pixel noise. We also performed sequential measurements of the phantoms in 2-D and 3-D modes to measure noise (from interpixel standard deviations) as a function of activity. To compensate for the difference in axial slice width between 2-D and 3-D images (due to the septa and reconstruction effects), we developed a smoothing kernel to apply to the 2-D data. After matching the resolution, the ratio of image-derived NSD values (NSD2D/NSD3D)2 averaged throughout the uniform phantom was in good agreement with the noise equivalent count (NEC) ratio (NEC3D/NEC2D). By comparing different phantoms, we showed that the attenuation and emission distributions influence the spatial noise distribution. The estimates of pixel noise for 2-D and 3-D images produced here can be applied in the weighting of PET kinetic data and may be useful in the design of optimal dose and scanning requirements for PET studies. The accuracy of these phantom-based noise formulas should be validated for any given imaging situation, particularly in 3-D, if there is significant activity outside the scanner field of view.     

Validation of Monte Carlo dose calculations near 125I sources in the presence of bounded heterogeneities

PURPOSE: Dose distributions around low energy (< 60 keV) brachytherapy sources, such as 125I, are known to be very sensitive to changes in tissue composition. Available 125I dosimetry data describe the effects of replacing the entire water medium by heterogeneous material. This work extends our knowledge of tissue heterogeneity effects to the domain of bounded tissue heterogeneities, simulating clinical situations. Our goals are three-fold: (a) to experimentally characterize the variation of dose rate as a function of location and dimensions of the heterogeneity, (b) to confirm the accuracy of Monte Carlo dose calculation methods in the presence of bounded tissue heterogeneities, and (c) to use the Monte Carlo method to characterize the dependence of heterogeneity correction factors (HCF) on the irradiation geometry. METHODS AND MATERIALS: Thermoluminescent dosimeters (TLD) were used to measure the deviations from the homogeneous dose distribution of an 125I seed due to cylindrical tissue heterogeneities. A solid water phantom was machined accurately to accommodate the long axis of the heterogeneous cylinder in the transverse plane of a 125I source. Profiles were obtained perpendicular to and along the cylinder axis, in the region downstream of the heterogeneity. Measurements were repeated at the corresponding points in homogeneous solid water. The measured heterogeneity correction factor (HCF) was defined as the ratio of the detector reading in the heterogeneous medium to that in the homogeneous medium at that point. The same ratio was simulated by a Monte Carlo photon transport (MCPT) code, using accurate modeling of the source, phantom, and detector geometry. In addition, Monte Carlo-based parametric studies were performed to identify the dependence of HCF on heterogeneity dimensions and distance from the source. RESULTS: Measured and calculated HCFs reveal excellent agreement (< or = 5% average) over a wide range of materials and geometries. HCFs downstream of 20 mm diameter by 10 mm thick hard bone cylinders vary from 0.12 to 0.30 with respect to distance, while for an inner bone cylinder of the same dimension, it varies from 0.72 to 0.83. For 6 mm diameter by 10 mm thick hard bone and inner bone cylinders, HCF varies 0.27-0.58 and 0.77-0.88, respectively. For lucite, fat, and air, the dependence of HCF on the 3D irradiation geometry was much less pronounced. CONCLUSION: Monte Carlo simulation is a powerful, convenient, and accurate tool for investigating the long neglected area of tissue composition heterogeneity corrections. Simple one dimensional dose calculation models that depend only on the heterogeneity thickness cannot accurately characterize 125I dose distributions in the presence of bone-like heterogeneities.     

Articular cartilage volume in the knee: semiautomated determination from three-dimensional reformations of MR images

PURPOSE: To determine the accuracy of semiautomated quantification of articular cartilage volume from three-dimensional (3D) reformations of magnetic resonance (MR) images. MATERIALS AND METHODS: Sagittal, fat-suppressed, 3D, spoiled gradient-recalled-echo MR imaging of two bovine and two human cadaver knees was performed. Articular cartilage volume was calculated from 3D reformations of the MR images by using a semiautomated program written at the authors' institution. Calculated volumes were compared with directly measured volumes of the surgically removed articular cartilage. RESULTS: The percentage of error of the MR imaging-determined volumes was 6.53% +/- 4.75 (mean +/- standard deviation). A strong correlation between the two sets of observations was shown (r=.997). Linear regression showed the calculated volumes to be highly accurate (slope=1.002, P>.25). Repeated reformations yielded volumes that were reproducible (mean absolute error, 0.013 mL +/- 0.019) and not significantly different from the measured volume (P>.10). CONCLUSION: Semiautomated quantification of knee articular cartilage from MR images yields highly accurate cartilage volumes.     

Dosimetry studies with TLDs for stereotactic radiation techniques for intraocular tumours

Between March 1993 and January 1997, stereotactic radiation techniques were used to irradiate 66 intraocular tumour patients with the Gamma Knife (Leksell Gamma Knife, model B unit) at the University of Vienna, Austria. This study investigates the dosimetry for stereotactic irradiation of ocular structures. For the dosimetry program KULA 4.4, Gamma Knife stereotactic irradiation of the eye represents an extreme frontal skull position. In addition, irradiation of the eye may be performed in the usual supine position in exceptional cases only. With the patient in the prone position, the dose planning program has to calculate with a significantly large number of single-beam extrapolations. In our first experiment we measured the isocentre dose for eight different gamma-angle positions, both in prone and supine positions, using TLD measurements in an Alderson head phantom. We found a maximum deviation of +/- 1.6% using these individually calibrated TLDs. In the second experiment we examined the dose cross profiles for the two most frequently used treatment positions (supine position, gamma = 65 degrees, and prone position, gamma = 140 degrees). For this purpose we implanted a specially designed TLD array into the orbit of a human cadaver head. We found excellent agreement of the dose values measured for the isocentre as well as the posterior part of the eye with orbit with deviations of less than -2.7%. However, for the anterior part of the eye, deviations between computer-generated calculations and the TLD measurements were found to range up to -30%. These differences were noticed both for supine and prone positions. For the Gamma Knife stereotactic irradiation of ocular tumours or pathologies, precautions should be taken to avoid significant underdosage in the anterior part of the radiation field.     

An anthropomorphic phantom study on the effect of midvertebral slice placement and region-of-interest positioning on the reproducibility of single-energy quantitative CT (QCT) of the spine

PURPOSE: The purpose of our study was to develop an anthropomorphic phantom with a 3D external reference system capable of geometrically describing the region of interest (ROI) of single-energy quantitative CT (QCT) scans and to study the reproducibility of ROI placement (volume) and bone mineral density (BMD) after operator-defined and algorithm-supported midvertebral slice (MVS) placement. METHOD: In three vertebrae (L1-3) of 10 human cadaveric spines placed in a water phantom, MVSs were defined by an operator and an algorithm-supported technique on lateral digital CT radiographs, and QCT scans were performed accordingly. The measurements were repeated once after repositioning the phantom on the CT table. ROIs of the trabecular bone were determined with a standard technique. The percentage of bone volume was calculated for one ROI not covered by the repetition (volume mismatch percent). RESULTS: Reproducibility with algorithm-supported MVS placement was superior to that of operator-defined positioning with regard to volume mismatch (mean +/- SD): 10.6+/-8.4 vs. 7.9+/-5.3%; and mean of paired BMDs (mean of three vertebral bodies): 2.7 vs. 1.5% (p < 0.05). CONCLUSION: The ROI volume mismatch of repeated QCT scans, which is approximately 10% of ROI volume, can be quantified with an external reference system. Automated placement is superior to the manual technique and should be used in clinical practice.     

Importance of computed tomography in irradiation planning for the thoracic region (author's transl)

The target volumes, anatomical distances and isodose curves in 62 patients undergoing irradiation of the thoracic region have been defined and compared for treatment planning, using an idealized transversal body section on the one hand, and computed tomograms on the other hand. 74% revealed nonconformance of the target volumes, and correction on the radiation field was therefore necessary in 62%, according to the CT-findings. Computed tomograms are superior to conventional treatment planning because they present individual body sections. Thus, deviations of the peak doses amounted to more than 10%: in the region of the mediastinum 7%, in the region of th lungs 29%, and in the region of the spinal cord 13% of the cases.     

An image-processing system for qualitative and quantitative volumetric analysis of brain images

In this work, we developed, implemented, and validated an image-processing system for qualitative and quantitative volumetric analysis of brain images. This system allows the visualization and quantitation of global and regional brain volumes. Global volumes were obtained via an automated adaptive Bayesian segmentation technique that labels the brain into white matter, gray matter, and cerebrospinal fluid. Absolute volumetric errors for these compartments ranged between 1 and 3% as indicated by phantom studies. Quantitation of regional brain volumes was performed through normalization and tessellation of segmented brain images into the Talairach space with a 3D elastic warping model. Retest reliability of regional volumes measured in Talairach space indicated errors of < 1.5% for the frontal, parietal, temporal, and occipital brain regions. Additional regional analysis was performed with an automated hybrid method combining a region-of-interest approach and voxel-based analysis, named Regional Analysis of Volumes Examined in Normalized Space (RAVENS). RAVENS analysis for several subcortical structures showed good agreement with operator-defined volumes. This system has sufficient accuracy for longitudinal imaging data and is currently being used in the analysis of neuroimaging data of the Baltimore Longitudinal Study of Aging.     

A simplified, practical echocardiographic approach for 3-dimensional surfacing and quantitation of the left ventricle: clinical application in patients with abnormally shaped hearts

The goal of this study was to validate the quantitative accuracy of a system for 3-dimensional (3D) echocardiographic reconstruction of the left ventricle to assess its volume and function in human beings by using 3 apical views as a simplified technique to promote practical clinical application. End-diastolic and end-systolic volumes (EDV, ESV) and ejection fraction (EF) were obtained by 3D echocardiography in 50 patients with dilated or geometrically distorted left ventricles and compared with values from magnetic resonance imaging (20 consecutive patients), angiography (22 consecutive patients), and radionuclide imaging (8 consecutive patients). Three-dimensional results were also compared with 2-dimensional (2D) echocardiographic estimates. Three-dimensional left ventricular reconstruction provided values that correlated and agreed well with pooled data from the other techniques for EDV (y = 0.93x + 9.1, r = 0.95, standard error of the estimate [SEE] = 15.2 mL, mean difference = -0.5 +/- 15.4 mL), ESV (y = 0.94x + 4.3, r = 0. 96, SEE = 11.4 mL, mean difference = 0.4 +/- 11.5 mL), and EF (y = 0. 90x + 4.1, r = 0.92, SEE = 6.2%, mean difference = -0.9 +/- 6.4%) (all mean differences not significant versus 0), with greater errors by 2D echocardiography. Intraobserver and interobserver variabilities of 3D echocardiography were less than 6% for EDV, ESV, and EF. The overall time for image acquisition and 3D reconstruction was 5 to 8 minutes. Although this 3D method uses only a small number of apical views, it accurately calculates EDV, ESV, and EF in patients with dilated and asymmetric left ventricles and is more accurate than 2D echocardiography. The flexible surface fit used to combine the 3 views provides a convenient visual output as well as quantitation. This simple and rapid 3D method has the potential to facilitate routine clinical applications that assess left ventricular function and changes that occur with remodeling.     

Conformal treatment planning for interstitial brachytherapy

PURPOSE: Quality of a brachytherapy application depends on the choice of the target volume, on the dose distribution homogeneity and radiation injury on critical tissue, which should be postulated by advanced brachytherapy treatment planning systems. MATERIAL AND METHODS: Basic imaging method for conformal treatment planning is the cross-sectional imaging. The clinical applicability of a new type 3D planning system using CT and/or MRT-simulation or US-simulation for planning purposes was studied. The planning system developed at Kiel University differs from usual brachytherapy planning systems because of the obligatory use of cross-sectional imaging as basic imaging method for reconstruction of structures of interest. Dose distribution and normal anatomy can be visualized on each CT/MRT/US slice as well as coronal, sagittal, axial and free chosen reconstruction (3D), as well as dose-volume histogram curves and special colour-coded visualization of dose homogeneity in the target can be analyzed. RESULTS: Because of the experience in the clinical routine, as well as on the base of 30 simultaneous planning procedures on both 2D (semi-3D) and 3D planning systems we observed similar time consumption. Advantages of 3D planning were the better interpretation of target delineation, delineation of critical structures as well as dose distribution, causing more accurate volume optimisation of dose distribution. CONCLUSION: Conformal brachytherapy treatment planning for interstitial brachytherapy means significant advantages for the clinical routine compared to 2D or semi-3D methods.     

Comparison of cardiac findings at necropsy in octogenarians, nonagenarians, and centenarians

The Toxoplasma gondii rhoptry protein Rop2 was expressed in Escherichia coli as a fusion protein containing 44 kDa of the 55-kDa mature Rop2, supplied with six histidyl residues at the N-terminal end (Rop2196-561). Humoral response during Toxoplasma infection of humans was analyzed by immunoglobulin G (IgG), IgA, and IgM enzyme-linked immunosorbent assay with Rop2196-561 as the antigen substrate. The analyzed sera were divided according to T. gondii-specific serological tests (IgG, IgA, or IgM indirect immunofluorescence and IgA or IgM immunosorbent agglutination assay) as group A (IgG+ IgA- IgM-; n = 35), group B (IgG+ IgA+ IgM+; n = 21), group C (IgG+ IgA+ IgM-; n = 5), and group D (IgG+ IgA- IgM+; n = 16). Twenty-six T. gondii-seronegative sera from individuals with other infections were also included (group E). Anti-Rop2 IgG antibodies were detected in 82.8% of group A sera and in 97.6% of the sera with acute-phase marker immunoglobulins (groups B, C, and D). The percentage of IgA antibody reactivity against Rop2196-561 was 17.1% in group A, 50% in group D, and 80.8% in groups B and C. The percentage of IgM antibody reactivity was 0% in groups A and C and 62% in groups B and D. Sera from group E failed to show IgA, IgM, or IgG antibody reactivity. Since T. gondii Rop2 elicits a strong humoral response from an early stage of infection, it is suggested that recombinant Rop2196-561 would be suitable for use in diagnostic systems, in combination with other T. gondii antigens, to detect specific IgG, IgA, and IgM antibodies.     

Pulmonary tuberculosis in the adult in a low prevalence area: is the radiological presentation changing?

BACKGROUND AND OBJECTIVE: To investigate the efficacy, predictability, stability, and safety of photorefractive keratectomy (PRK) with scanning spot ablation for the treatment of myopia of less than -6.0 D. PATIENTS AND METHODS: Twenty eyes of 20 patients (11 men, 9 women) were enrolled into the study. The mean age was 26.2 +/- 5.4 years. Mean spherical equivalent myopia was -3.53 +/- 1.13 D, ranging from -2.25 to -6.00 D. Patients underwent excimer laser PRK for the treatment of myopia. Follow-up time was at least 24 months in all patients. RESULTS: Mean spherical equivalent refraction was +0.84 +/- 0.99 D at 1 month, +0.19 +/- 0.54 at 3 months, -0.01 +/- 0.53 at 12 months, and -0.13 +/- 0.50 at 24 months. There was a mean regression of 0.65 D between 1 and 3 months. At 24 months, 16 (80%) of the eyes remained within +0.50 D of emmetropia and 18 (90%) of the eyes remained within +/- 1.0 D of emmetropia. Nineteen (95%) of the eyes had uncorrected visual acuity of 20/40 or better. The mean corneal haze score was maximum at 3 months (0.88 +/- 0.22). There was no clinically significant corneal haze (greater than 2+). One eye (5%) lost 2 or more lines of best-corrected visual acuity. CONCLUSION: Excimer laser PRK with the scanning spot ablation technique is effective, predictable, stable, and safe for the treatment of myopia of less than -6.0 D.     

Age-related changes in D2 receptor binding with iodine-123-iodobenzofuran SPECT

The purpose of this study was to evaluate the effects of age on D2 receptor binding with 123I-iodobenzofuran (IBF) SPECT. METHODS: Subjects were 40 healthy volunteers (age 19-83 yr), including 6 who had test/retest studies. Scans were acquired with a triple-head SPECT camera 3 hr postinjection of IBF (300 MBq). Striatal regions (caudate and putamen) were defined by two different region-of-interest (ROI) sets consisting of large volumes [(CLVs), 2.2 and 6.6 m] and small volumes [(SVs), 0.6 and 1.3 ml]. D2 binding (Rv=V3/V2) was quantified using our previously proposed multilinear regression technique. Effects of age on D2 binding were evaluated by fitting linear, exponential and logarithmic models. RESULTS: The mean Rvs were 26% lower than LV for both putamen and caudate than the corresponding values from the SV due to the partial-volume effect. Although the identifiability of Rv using SV deteriorated slightly, the test/retest reproducibility of Rv measurements was equally excellent for LV and SV. The mean Rvs were 11% higher for putamen compared with those for caudate. D2 binding declined significantly with age (p < 10(-5)) for all three models. The nonlinear models were slightly superior to the linear model in describing the relationship between Rv and age. In these models, D2 binding declined with age, equally for caudate and putamen at 7%-13% per decade; the decline was progressively smaller with age. CONCLUSION: IBF SPECT permitted reliable measurements of D2 binding in the caudate or putamen separately using small ROI volumes that significantly improved the quantitation loss from the partial-volume effect. Our results agreed with previous PET and postmortem findings of D2 binding losses with age. However, these age effects may be nonlinear. Age-related changes in D2 binding must be taken into consideration in clinical IBF SPECT investigations.     

Changes in RBE of 14-MeV (d + T) neutrons for V79 cells irradiated in air and in a phantom: is RBE enhanced near the surface?

PURPOSE: The relative biological effectiveness (RBE) for inactivation of V79 cells was determined as function of dose at the Heidelberg 14-MeV (d + T) neutron therapy facility after irradiation with single doses in air and at different depths in a therapy phantom. Furthermore, to assess the reproducibility of RBE determinations in different experiments we examined the relationship between the interexperimental variation in radiosensitivity towards neutrons with that towards low LET 60Co photons. METHODS: Clonogenic survival of V79 cells was determined using the colony formation assay. The cells were irradiated in suspension in small volumes (1.2 ml) free in air or at defined positions in the perspex phantom. Neutron doses were in the range, Dt = 0.5-4 Gy. 60Co photons were used as reference radiation. RESULTS: The radiosensitivity towards neutrons varied considerably less between individual experiments than that towards photons and also less than RBE. However, the mean sensitivity of different series was relatively constant. RBE increased with decreasing dose per fraction from RBE = 2.3 at 4 Gy to RBE = 3.1 at 0.5 Gy. No significant difference in RBE could be detected between irradiation at 1.6 cm and 9.4 cm depth in the phantom. However, an approximately 20% higher RBE was found for irradiation free in air compared with inside the phantom. Combining the two effects, irradiation with 0.5 Gy free in air yielded an approximately 40% higher RBE than a dose of 2 Gy inside the phantom. CONCLUSION: The measured values of RBE as function of dose per fraction within the phantom is consistent with the energy of the neutron beam. The increased RBE free in air, however, is greater than expected from microdosimetric parameters of the beam and may be due to slow recoil protons produced by interaction of multiply scattered neutrons or to an increased contribution of alpha particles from C(n, alpha) reactions near the surface. An enhanced RBE in subcutaneous layers of skin combined with an increase in RBE at low doses per fraction outside the target volume could potentially have significant consequences for normal tissue reactions in radiotherapy patients treated with fast neutrons.     

Capillarization of the muscular tissue of the Black Sea dolphin Phocaena phocaena

Studies have been made on morphological and diffusion parameters of capillaries in cardiac and skeletal muscles of the dolphin P. phocaena. As compared to that in terrestrial mammals, the degree of capillarization of muscle tissue in the dolphin was found to be higher. Higher density of capillaries, as well as shorter radii of diffusion and smaller volumes of tissue cylinders, are responsible for more intensive supply of oxygen per tissue volume unit in dolphins.     

Low-dose spiral computed tomography for measuring abdominal fat volume and distribution in a clinical setting

OBJECTIVES: Computed tomography (CT) has been used to measure body composition, however, a technique with reduced radiation exposure has not yet been introduced. This study tested a low-dose spiral CT technique on a phantom to determine its validity and reproducibility. The method was then applied for volume and distribution measurements in patients. DESIGN: Construction and measurement of a phantom followed by measurement of patients referred to CT for clinical indications. SETTING: Radiology Department, University Hospital. SUBJECTS: Twenty-four post-gastrectomy patients. INTERVENTION: A 22 cm phantom with a known amount of water and fat was scanned using high- and low-dose technique, standard and double table speed during a volumetric scan. The low-dose technique was implemented in the patient group. Total volume, total fat and four defined compartmental fat volumes in the truncal area were measured. RESULTS: The mean fat volume measured using the low-dose CT technique in the phantom was 0.2% above the actual fat content. The coefficient of variation for this method was 5%. By using low-dose, double speed instead of standard-dose technique, radiation exposure to the skin was decreased by more than 90% (equivalent to 4 mGy) of what is used in diagnostic imaging. The patient scans showed that no significant differences in BMI and total measured volume existed between female and male patients, but percent fat and percent subcutaneous fat were significantly larger in women (P = 0.006 and 0.002, respectively), as were percent intraabdominal and mediastinal fat in men (P = 0.002 and 0.003 respectively). CONCLUSIONS: Low-dose spiral CT accurately measures fat volume in vitro, and can be used in vivo for compartmental fat measurements.