Radiation Exposure of Medical Staff Conducting Stress Myocardial Perfusion Imaging.

Background: The myocardial perfusion stress conducted by physicians and nurses requires two imaging sessions, one during stress and the other during rest. Echocardiography is sometimes performed before delayed imaging, and medical laboratory technicians (MLTs) have similar exposure in such cases. This study was designed to investigate the radiation exposure of physicians, nurses, radiologists, and MLTs involved in thallium-201 chloride (201TlCl) stress myocardial perfusion imaging and echocardiography, the details of which have not been reported to date. Methods: The dose rate at thallium-201 (201Tl) was examined using a cylindrical phantom. The exposure of physicians, nurses, and radiologists involved in the 201TlCl stress myocardial perfusion imaging was measured using pocket dosimeters, and that of the MLTs in charge of echocardiography were measured using glass-batch dosimeters. Results: The attenuation of radiation exposure from the phantom with distance was 95% at 50 cm from the center of the phantom, demonstrated that the attenuation of the exposure dose increased with distance. The exposure dose for physicians, nurses, and radiological technologists that participated in 201TlCl stress myocardial perfusion imaging was 0.20-0.23 µSv per exam, whereas it was 6.67-10.00 µSv per exam for MLTs. Conclusion: This study measured the dose received by physicians, nurses, and radiological technologists during stress MPI and the dose received by MLTs during echocardiography. The results provided advanced knowledge for the management of dose received by medical personnel.

Normal model construction for statistical image analysis of torso FDG-PET images based on anatomical standardization by CT images from FDG-PET/CT devices.

PURPOSE: A better understanding of the standardized uptake value (SUV) ranges of fludeoxyglucose positron emission tomography (FDG-PET) is crucial for radiologists. We have developed a statistical image analysis method for FDG-PET imaging of the torso, based on comparisons with normal data. The purpose of this study was to verify the accuracy of the normal model and usefulness of the statistical image analysis method by using typical cancer cases in the liver, lungs, and abdomen. METHODS: Our study and the data collection (49 normal and 34 abnormal cases, in terms of PET/CT findings) were approved by the institutional review board. Our scheme consisted of the following steps: (1) normal model construction, (2) anatomical standardization of patient images, and (3) Z-score calculation to show the results of the statistical image analysis. To validate the Z-score index, we sampled 3603 and 1270 voxels in normal organs and abnormal regions, respectively, from the liver, lungs, and the abdomen. We then obtained the SUV and Z-score for each region. A receiver operating characteristics (ROC) analysis-based method was performed to evaluate the discrimination performances of the SUV and Z-score. RESULTS: The discrimination performances of the SUV and Z-score for the objective regions of interest (ROIs) were evaluated by the areas under the ROC curves (AUCs). As a result of the ROC analysis and statistical tests, all AUCs were found to be larger than 0.98. When the ROIs in the objective regions were combined, the mean AUCs of the Z-score and SUV were 0.99 and 0.98, respectively, the difference being statistically significant ([Formula: see text]). CONCLUSIONS: The results suggested the possibility of applying a quantitative image reading method for torso FDG-PET imaging. Furthermore, a combination of the SUV and Z-score may provide increased accuracy of the determination methods, such as computer-aided detection and diagnosis.

A robust conversion method of radioactivities between plastic and NaI scintillation well counters for long-term quality control and quality assurance.

PURPOSE: The purpose of this study is to specify a simple procedure for a robust data conversion of radioactivity value between plastic scintillator (PL) and NaI scintillator (NaI) devices. MATERIALS AND METHODS: The radioactivity estimate of 100 blood samples was measured by the two devices. The two radioactivities were plotted on the same graph. The least-squares method was applied to obtain the conversion function. The differences between the actual radioradioy (N) from the NaI device and the estimated radioactivity for NaI (N') from the PL device activity (P) were statistically analyzed. RESULTS: N' was determined from P as N' = 4.45 P + 6.28 with high correlation (r = 0.997). The Bland-Altman analysis between N' and N showed no fixed bias and no proportional bias. CONCLUSIONS: A hundred blood samples using a fixed type of sample tubes and a fixed radionuclide may be required to set up the robust conversion function.

Development of a myocardial phantom and analysis system toward the standardization of myocardial SPECT image across institutions.

OBJECTIVE: We developed a novel myocardial phantom and analysis program to standardize using a quantitative index to objectively evaluate the image quality. We aimed to reveal whether our proposed phantom and analysis program are suitable for image standardization. METHODS: An evaluation system of myocardial image based on technical grounds (EMIT) phantom was developed to standardize the image quality of myocardial SPECT and was constructed with the lung and myocardium in the thorax phantom; the myocardial phantom included five normal areas and eight defective areas with four defects in size (5, 10, 15, and 20 mm) and four defects in thickness (10, 7.5, 5, and 2.5 mm). Therefore, this phantom was appropriate to simultaneously simulate eight different defects and normal myocardium. The %rate value, calculated using the region of interest method, and the %count value, calculated from the profile method, were automatically analyzed to evaluate myocardial defects. The phantom was validated using difference in count levels and filter parameters compared with those in previously reported models. RESULTS: The average %count of eight defects by 0.3, 0.4, 0.5, and 0.6 cycles/cm were 56.8, 47.4, 44.3, and 43.4 %, respectively, whereas the %count for 0.3 cycles/cm was significantly higher than that for 0.5 and 0.6 cycles/cm. The uniformity between full- and half-time images was 16.5 ± 4.2 and 18.7 ± 5.5 % for integral uniformity and 3.4 ± 1.2 and 3.4 ± 1.3 % for differential uniformity, respectively, revealing a significant difference in integral uniformity between the two acquisition times. Visual differences in defects were evident in full-time images between 0.30 and 0.50 cycles/cm, and defect detectability of the myocardial image at 0.30 cycles/cm was poor. Normal myocardial thickness widened in comparison with images at 0.50 cycles/cm. Compared with full-time myocardial image at the same cut-off frequency, the half-time myocardial image demonstrated inhomogeneous distribution and thickness of the normal myocardium. CONCLUSION: We developed a new phantom and program to standard image quality among multicenter for myocardial SPECT. The EMIT phantom and quantitative indices were useful for evaluating image quality. The physical characteristics of the image quality, including defects and uniformity, were properly measured by this method.

Development of a single-photon-counting camera with use of a triple-stacked micro-channel plate.

At the quantum-mechanical level, all substances (not merely electromagnetic waves such as light and X-rays) exhibit wave­particle duality. Whereas students of radiation science can easily understand the wave nature of electromagnetic waves, the particle (photon) nature may elude them. Therefore, to assist students in understanding the wave­particle duality of electromagnetic waves, we have developed a photon-counting camera that captures single photons in two-dimensional images. As an image intensifier, this camera has a triple-stacked micro-channel plate (MCP) with an amplification factor of 10(6). The ultra-low light of a single photon entering the camera is first converted to an electron through the photoelectric effect on the photocathode. The electron is intensified by the triple-stacked MCP and then converted to a visible light distribution, which is measured by a high-sensitivity complementary metal oxide semiconductor image sensor. Because it detects individual photons, the photon-counting camera is expected to provide students with a complete understanding of the particle nature of electromagnetic waves. Moreover, it measures ultra-weak light that cannot be detected by ordinary low-sensitivity cameras. Therefore, it is suitable for experimental research on scintillator luminescence, biophoton detection, and similar topics.

Quantitative Analysis of Torso FDG-PET Scans by Using Anatomical Standardization of Normal Cases from Thorough Physical Examinations.

Understanding of standardized uptake value (SUV) of 2-deoxy-2-[18F]fluoro-d-glucose positron emission tomography (FDG-PET) depends on the background accumulations of glucose because the SUV often varies the status of patients. The purpose of this study was to develop a new method for quantitative analysis of SUV of FDG-PET scan images. The method included an anatomical standardization and a statistical comparison with normal cases by using Z-score that are often used in SPM or 3D-SSP approach for brain function analysis. Our scheme consisted of two approaches, which included the construction of a normal model and the determination of the SUV scores as Z-score index for measuring the abnormality of an FDG-PET scan image. To construct the normal torso model, all of the normal images were registered into one shape, which indicated the normal range of SUV at all voxels. The image deformation process consisted of a whole body rigid registration of shoulder to bladder region and liver registration and a non-linear registration of body surface by using the thin-plate spline technique. In order to validate usefulness of our method, we segment suspicious regions on FDG-PET images manually, and obtained the Z-scores of the regions based on the corresponding voxels that stores the mean and the standard deviations from the normal model. We collected 243 (143 males and 100 females) normal cases to construct the normal model. We also extracted 432 abnormal spots from 63 abnormal cases (73 cancer lesions) to validate the Z-scores. The Z-scores of 417 out of 432 abnormal spots were higher than 2.0, which statistically indicated the severity of the spots. In conclusions, the Z-scores obtained by our computerized scheme with anatomical standardization of torso region would be useful for visualization and detection of subtle lesions on FDG-PET scan images even when the SUV may not clearly show an abnormality.

Performance characteristics of a novel clustered multi-pinhole technology for simultaneous high-resolution SPECT/PET.

OBJECTIVE: Versatile emission computed tomography (VECTor) for small-animal imaging enables fully simultaneous SPECT/PET image acquisition based on clustered multi-pinhole collimation. The present study experimentally evaluated the detailed performance characteristics of the clustered multi-pinhole system for simultaneous (99m)Tc and (18)F imaging from the user perspective. METHODS: Spatial resolution, sensitivity, count rate linearity were determined for the VECTor system (MILabs). Two hot-rod micro-resolution phantoms with 6 sectors were created to test the resolution of (99m)Tc and (18)F. Sensitivity and count rate linearity were measured by scanning (99m)Tc and (18)F point sources positioned at the center of the field of view. Furthermore, we quantified the influence of (18)F on (99m)Tc SPECT images. The ratios of SPECT counts on the (99m)Tc-only and simultaneous (18)F-(99m)Tc at various time points were evaluated as a function of the (18)F-to-(99m)Tc activity concentration ratio. RESULTS: The 0.5-mm hot-rods can be visually distinguished in the (99m)Tc image, and 0.8-mm rods for (18)F remained clearly visible. The point-source sensitivity was 2800 cps/MBq for (99m)Tc and 2899 cps/MBq for (18)F, respectively. Count rates up to 120,000 cps for one bed position were linear for the activity. Spill-over from (18)F into (99m)Tc SPECT images was negligible when the activity concentration of the administered (18)F solution exceeded that of the (99m)Tc solution by up to a factor of 2. CONCLUSIONS: We evaluated the performance characteristics of the VECTor that lead to determination of the optimal administered doses of (99m)Tc and (18)F tracers. We found that the VECTor achieved high resolution and high sensitivity as well as good (99m)Tc and (18)F linearity. Simultaneous SPECT/PET imaging with (99m)Tc and (18)F tracers, and stand-alone (99m)Tc and (18)F imaging using clustered-pinhole collimators is feasible and practical for a wide range of research applications using small animals.

Postprandial decrease in vascular resistance correlated with change in second derivative of finger plethysmogram in young subjects.

BACKGROUND: The second derivative of the finger plethysmogram (SDPTG) comprises five waves termed a to e. The magnitudes of waves b-e are normalized by that of wave a for within- and between-patient comparison. In the present study, affects of meal ingestion for SDPTG in young and elderly subjects are examined. SUBJECTS AND METHODS: Mean arterial pressure and SDPTG before and after meal ingestion in young and elderly subjects were measured. For young subjects, stroke volume and pulse rate were also measured, and the total peripheral resistance (TPR) of the blood vessels was analyzed. Relationship between TPR and the ratio of the peak of SDPTG in young subjects was also analyzed. RESULTS: In young subjects, postprandial d/a was significantly larger and TPR was smaller than before intake and was linearly and significantly correlated with TPR. An increase in the postprandial d/a was also observed in the elderly subjects who were not undergoing hypertension treatment. However, this increase was not observed in elderly subjects who were treated for hypertension. CONCLUSIONS: Change in d/a is considered to be an index of change in TPR. TPR is considered to be decreased by agents for treatment of hypertension, and meal ingestion does not appear to further decrease TPR. These results are considered to be useful for understanding cardiodynamics surrounding meal ingestion.

Compression stocking length effects on arterial blood pressure and heart rate following head-up tilt in healthy volunteers.

BACKGROUND: Change in posture from supine to standing induces a footward fluid shift. This shift might decrease arterial pressure (AP) and induce orthostatic hypotension. To prevent decrease in AP, compression stockings are recommended, but the effects of various lengths have not been compared. OBJECTIVE: The aim was to compare AP and heart rate (HR) by compression stocking length during head-up tilt (HUT). METHODS: The effects of elastic compression stockings of three lengths on AP and HR were examined at the onset of HUT. The stockings were knee-high, compressing the foot and calf; thigh-high, compressing the toe to the thigh; and waist-high, compressing the toe to the waist. RESULTS: AP did not significantly change at the onset of HUT without stockings or with any length of stockings compared with the AP in the supine position. HR was significantly higher at the onset of HUT without stockings and with the knee-high and thigh-high stockings than that during supine position. No significant difference in HR was observed among the three conditions. However, the HR increase was significantly depressed with the waist-high stockings. DISCUSSION: These results suggest that the use of waist-high stockings that afford abdominal compression is needed to affect cardiovascular dynamics at the onset of HUT and may prevent orthostatic hypotension.

RR interval variability during galvanic vestibular stimulation correlates with arterial pressure upon head-up tilt.

RR interval variability (RRIV) in the supine position without and with galvanic vestibular stimulation (GVS (off) and GVS (on), respectively), changes in mean arterial pressure (MAP) at the onset of 60° head-up tilt (HUT) during GVS (off), and their relationship were analyzed in 25 healthy young subjects. MAP decreased by less than 5mmHg or increased upon HUT in 12 subjects (UP), but MAP decreased by more than 5mmHg in 13 subjects (DOWN). Applying sinusoidal GVS of 2mA at a random frequency of 0.2 to 10.0Hz did not change the RR intervals or MAP. However, the high frequency component (HF) of RRIV increased in both UP and DOWN subjects. The increase in DOWN subjects was larger than that in UP subjects. The ratio of the low frequency component to HF (L/H) increased in UP subjects during GVS (on), but did not reach a significant level in DOWN subjects. The changes in the HF were significantly correlated with changes in MAP at the onset of HUT; i.e., the subjects with larger increases in the HF during GVS (on) showed larger decreases in MAP. Thus, GVS or vestibular input during HUT possibly activates the vagal nerves, and the dominance of excitation in sympathetic or vagal nerves during vestibular stimulation is important for controlling MAP at the onset of HUT.

Reconstruction of semiautomated cardiac regions of interest using iodine-123 metaiodobenzylguanidine myocardial scintigraphy.

INTRODUCTION: Analysis using cardiac iodine-123 metaiodobenzylguanidine (MIBG) scintigraphy with regions of interest (ROIs) is useful for assessing myocardial sympathetic activity. However, manual placement of the cardiac ROI is sometimes difficult because myocardial MIBG uptake is reduced in patients with heart failure. A new method was developed to reconstruct the semiautomated cardiac ROI in a sympathetic denervated heart. MATERIALS AND METHODS: Using dynamic planar data, a summed image was generated and the matrix size was changed. Then, the radial count profiles originating from the center of the left ventricle were generated to extract the myocardial count profiles. An asymmetric Gaussian distribution was fitted to each profile and the epicardial border was defined by the threshold method. This program was tested in 50 patients, and its reproducibility was validated when compared with the manual tracing method. RESULTS: The semiautomated method yielded a better quality image compared with the standard image with higher counts. Cardiac ROIs were generated successfully in each patient within normal limits. The intraobserver and interobserver agreements were excellent (P<0.0001 each). This approach showed a significantly higher consistency in measuring the heart-to-mediastinum ratio as compared with the manual tracing method (P<0.05). CONCLUSION: The semiautomated method is useful in generating cardiac ROIs with high reproducibility in myocardial MIBG imaging.

[Evaluation of the edge enhancement effect of phase contrast imaging using newly-developed photostimulable phosphor plate].

We investigated whether the use of a newly developed columnar-crystal-type photostimulable-phosphor plate (CP1M200, referred to as system C) helps to provide improved edge-enhanced effect in phase contrast imaging. Physical characteristics of 2 conventional particulate-crystal-type photostimulable-phosphor plates (RP-5PM, referred to as system A and RP-6M, referred to as system B) and system C were measured. Then, an acrylic plate phantom and RMI152 phantom were imaged using 3 types of plates, and the edge-enhancement effects were evaluated based on the profile curve of the acrylic plate phantom. Visual evaluation of the RMI152 phantom images was conducted. The results showed that the modulation transfer function (MTF) of system C was superior to those of the other systems. The WS of system C was superior to those of the other systems in the low frequency band region, and inferior to those of the other systems in the high frequency band region. The presence of an edge-enhanced image was not detectable in the profile curve of the acrylic plate in system A, although that was shown in systems B and C due to their excellent sharpness. In the visual image evaluation of the RMI152 phantom, image quality of system C was superior to those of the other systems. Phase contrast imaging with a digital detector of a columnar-crystal-type photostimulable-phosphor plate is considered to provide improved edge-enhancement over that of conventional plates.

Image-quality assessment method for digital phase-contrast imaging based on two-dimensional power spectral analysis.

With use of the phase shift of X-rays that occurs when they pass through an object, phase-contrast imaging (herein referred to as "phase imaging") can produce images different from those of conventional contact imaging (herein referred to as "conventional imaging"). For this reason, assessment of the image quality based on noise-equivalent quanta (NEQ) and detective quantum efficiency (DQE) which does not include object-based information may not be appropriate for comparison of image quality between phase and conventional images. As an alternative method, we conceived a new image-quality assessment method with images that contain information about an object. First, we constructed images with an object and without an object under the same imaging parameters; then, we obtained two-dimensional power spectra by Fourier transform of those images. Second, we calculated the radial direction distribution function with the power spectra, and the distribution of signal intensity, which we defined as a signal intensity distribution function (SIDF). In this way, differences in image quality were evaluated relatively based on the SIDF of the imaged object. In our study, we first confirmed that phase-imaging evaluation was not appropriate by comparing NEQ and DQE of conventional, magnification, and phase imaging. Further, comparing the image quality of projected plant seeds by employing conventional, magnification, and phase imaging, we found that the phase-imaging method provided a higher image quality regarding edge sharpness than did conventional and magnification imaging. Therefore, based on these results, our image assessment method is considered useful for evaluation of images which include object-based information.

Mobility of an elastic glove for extravehicular activity without prebreathing.

INTRODUCTION: The current U.S. extravehicular activity (EVA) suit is pressurized at 0.29 atm, which is much lower than the pressures of sea level and inside a space station. Higher pressure can reduce the risk of decompression sickness (DCS), but mobility would be sacrificed. We have demonstrated that a glove and sleeve made of elastic material increased mobility when compared with those made of nonelastic material, such as that found in the current suit. We hypothesized that an elastic glove of 0.65 atm that has no risk of DCS also has greater mobility compared with a non-elastic glove of 0.29 atm. METHODS: The right hands of 10 healthy volunteers were studied in a chamber with their bare hands at normal ambient pressure, after donning a non-elastic glove with a pressure differential of 0.29 atm, and after donning an elastic glove with a pressure differential of 0.29 and 0.65 atm. Range of motion (ROM) of the index finger and surface electromyography (EMG) amplitudes during finger flexion were measured. RESULTS: ROM with gloves was significantly smaller than that of bare hands, but was similar between conditions of gloves regardless of elasticity and pressure differentials. However, EMG amplitudes with the elastic glove of 0.29 and 0.65 atm were significantly smaller than those with the non-elastic glove of 0.29 atm. DISCUSSION: The results suggest that mobility of the elastic glove of 0.65 atm may be better than that of the non-elastic glove of 0.29 atm, similar to that used in the current EVA suit.

Quantitative mapping of basal and vasareactive cerebral blood flow using split-dose 123I-iodoamphetamine and single photon emission computed tomography.

A new method has been developed for diffusible tracers, to quantify CBF at rest and after pharmacological stress from a single session of dynamic scans with dual bolus administration of a radiotracer. The calculation process consisted of three steps, including the procedures of incorporating background radioactivity contaminated from the previous scan. Feasibility of this approach was tested on clinical SPECT studies on 16 subjects. Two sequential SPECT scans, 30 min apart, were carried out on each subject, after each of two split-dose administrations of 111 MBq IMP. Of these, 11 subjects received acetazolamide at 10 min before the second IMP injection. Additional PET scans were also carried out on 6 subjects on a separate day, at rest and after acetazolamide administration. The other 5 subjects were scanned only at rest during the whole study period. Quantitative CBF obtained by this method was in a good agreement with those determined with PET (y(ml/100 g/min)=1.07x(ml/100 g/min)-1.14, r=0.94). Vasareactivity was approximately 40% over the whole cerebral area on healthy controls, which was consistent with a literature value. Reproducibility of CBF determined in the rest-rest study was 1.5+/-5.7%. Noise enhancement of CBF images, particularly the second CBF, was reduced, providing reasonable image quality. Repeat assessment of quantitative CBF from a single session of scans with split-dose IMP is accurate, and may be applied to clinical research for assessing vascular reactivity in patients with chronic cerebral vascular disease.

[Usefulness of attenuation correction with transmission source in myocardial SPECT].

Attenuation correction in SPECT has been used for uniformly absorptive objects like the head. On the other hand, it has seldom been applied to nonuniform absorptive objects like the heart and surrounding lungs because of the difficulty and inaccuracy of data processing. However, since attenuation correction using a transmission source recently became practical, we were able to apply this method to a nonuniform absorptive object. Therefore, we evaluated the usefulness of this attenuation correction system with a transmission source in myocardial SPECT. The dose linearity, defect/normal ratio using a myocardial phantom, and myocardial count distribution in clinical cases was examined with and without the attenuation correction system. We found that all data processed with attenuation correction were better than those without attenuation correction. For example, in myocardial count distribution, while there was a difference between men and women without attenuation correction, which was considered to be caused by differences in body shape, after processing with attenuation correction, myocardial count distribution was almost the same in all cases. In conclusion, these results suggested that attenuation correction with a transmission source was useful in myocardial SPECT.

Ray tracing analysis of overlapping objects in refraction contrast imaging.

We simulated refraction contrast imaging in overlapping objects using the ray tracing method. The easiest case, in which two columnar objects (blood vessels) with a density of 1.0 [g/cm3], run at right angles in air, was calculated. For absorption, we performed simulation using the Snell law adapted to the object's boundary. A pair of bright and dark spot results from the interference of refracted X-rays where the blood vessels crossed. This has the possibility of increasing the visibility of the image.

Evaluation of edge effect due to phase contrast imaging for mammography.

It is well-known that the edge effect produced by phase contrast imaging results in the edge enhancement of x-ray images and thereby sharpens those images. It has recently been reported that phase contrast imaging using practical x-ray tubes with small focal spots has improved image sharpness as observed in the phase contrast imaging with x-ray from synchrotron radiation or micro-focus x-ray tubes. In this study, we conducted the phase contrast imaging of a plastic fiber and plant seeds using a customized mammography equipment with a 0.1 mm focal spot, and the improvement of image sharpness was evaluated in terms of spatial frequency response of the images. We observed that the image contrast of the plastic fiber was increased by edge enhancement, and, as predicted elsewhere, spectral analysis revealed that as the spatial frequencies of the x-ray images increased, so did the sharpness gained through phase contrast imaging. Thus, phase contrast imaging using a practical molybdenum anode tube with a 0.1 mm-focal spot would benefit mammography, in which the morphological detectability of small species such as microcalcifications is of great concern. And detectability of tumor-surrounded glandular tissues in dense breast would be also improved by the phase contrast imaging.