Low-energy Collimator Research Articles

A nine-pixel matched collimator for low- and medium-energy SPECT imaging

For low-and medium-energy SPECT imaging without collimator exchange, a wide-aperture parallel-hole collimator—called a ‘nine-pixel matched collimator (9-PMC)’—was developed. The hole size of the 9-PMC is matched to nine detector pixels, giving nine (3 × 3) pixels per collimator hole. The 9-PMC was designed to reduce the penetration of medium-energy gamma rays. The performance of the 9-PMC for 99mTc and 111In gamma-ray energy was experimentally evaluated and compared with that of a low-energy collimator. A CdTe detector with 1.4 mm pitch was used in conjunction with the 9-PMC. A four-pixel matched collimator (‘4-PMC’ hereafter) with hole size matched to four detector pixels was also used as a high-sensitivity low-energy collimator. Hole pitch, hole length and septum thickness of the 4-PMC/9-PMC were 2.8/4.2 mm, 26.0/33.4 mm and 0.4/1.0 mm, respectively. The system sensitivities of the 4-PMC and 9-PMC for 99mTc gamma rays were 221 cps MBq−1 and 211 cps MBq−1, respectively. For the 4-PMC, system sensitivities for 171 and 245 keV 111In gamma rays were 232 cps MBq−1 and 503 cps MBq−1, respectively, while for the 9-PMC, the system sensitivities for 171 and 245 keV 111In gamma rays were 145 cps MBq−1 and 106 cps MBq−1, respectively. Spatial resolution of the collimator was analyzed by using modulation transfer functions (MTFs) obtained from the line-source profiles. The results of this analysis demonstrate that the 9-PMC for 99mTc had frequency ranges for similar (or higher) and lower MTF values compared with those for the 4-PMC, while the 9-PMC for 111In had higher MTF values than those for the 4-PMC at a wide frequency range. Hot-sphere phantom images showed that the image contrast of the 9-PMC for 99mTc gamma rays is comparable to that of the 4-PMC, while that of the 9-PMC for 111In gamma rays is higher than that of the 4-PMC. The developed SPECT with the 9-PMC and CdTe detector provided higher image quality for 111In gamma rays, or comparable image quality for 99mTc gamma rays, compared with that of a low-energy collimator.

骨等価溶液を用いた骨SPECT評価用ボディファントムの開発

We developed a custom-designed phantom for bone single photon emission computed tomography (SPECT)-specific radioactivity distribution and linear attenuation coefficient. The aim of this study was to evaluate the accuracy of the phantom. The lumbar phantom consisted of the trunk of a body phantom (background) containing a cylinder (vertebral body), a sphere (tumor), and a T-shaped container (processus). The vertebral body, tumor, and processus phantoms contained a K(2)HPO(4) solution of bone equivalent density and 50, 300 and 50 kBq/mL of (99m)Tc, respectively. The body phantom contained 8 kBq/mL of (99m)Tc solution. SPECT images were acquired using low-energy high-resolution collimation, a 128 × 128 matrix and 120 projections over 360° with a dwell time of 15 sec/view × 4 times. Thereafter, CT images were acquired at 130 kV and 70 ref mAs using adaptive dose modulation. The SPECT data were reconstructed with ordered subset expectation maximization with three-dimensional, scatter, and CT-based attenuation correction. Count ratio, linear attenuation coefficient (LAC), and full-width at half-maximum (FWHM) were measured. Count ratios between the background, the vertebral body, and the tumor in SPECT images were 463.8: 2888.0: 15150.3 (1: 6.23: 32.7). The LAC of the background and vertebral body in the CT-derived attenuation map were 0.155 cm⁻¹ and 0.284 cm⁻¹, respectively, and the FWHM measured from the processus was 15.27 mm. The precise counts and LAC indicated that the phantom was accurate and could serve as a tool for evaluating acquisition, reconstruction parameters, and quantitation in bone SPECT images.

Characterization of parallel-hole collimator using Monte Carlo Simulation.

Objective:Accuracy of in vivo activity quantification improves after the correction of penetrated and scattered photons. However, accurate assessment is not possible with physical experiment. We have used Monte Carlo Simulation to accurately assess the contribution of penetrated and scattered photons in the photopeak window.Materials and Methods:Simulations were performed with Simulation of Imaging Nuclear Detectors Monte Carlo Code. The simulations were set up in such a way that it provides geometric, penetration, and scatter components after each simulation and writes binary images to a data file. These components were analyzed graphically using Microsoft Excel (Microsoft Corporation, USA). Each binary image was imported in software (ImageJ) and logarithmic transformation was applied for visual assessment of image quality, plotting profile across the center of the images and calculating full width at half maximum (FWHM) in horizontal and vertical directions.Results:The geometric, penetration, and scatter at 140 keV for low-energy general-purpose were 93.20%, 4.13%, 2.67% respectively. Similarly, geometric, penetration, and scatter at 140 keV for low-energy high-resolution (LEHR), medium-energy general-purpose (MEGP), and high-energy general-purpose (HEGP) collimator were (94.06%, 3.39%, 2.55%), (96.42%, 1.52%, 2.06%), and (96.70%, 1.45%, 1.85%), respectively. For MEGP collimator at 245 keV photon and for HEGP collimator at 364 keV were 89.10%, 7.08%, 3.82% and 67.78%, 18.63%, 13.59%, respectively.Conclusion:Low-energy general-purpose and LEHR collimator is best to image 140 keV photon. HEGP can be used for 245 keV and 364 keV; however, correction for penetration and scatter must be applied if one is interested to quantify the in vivo activity of energy 364 keV. Due to heavy penetration and scattering, 511 keV photons should not be imaged with HEGP collimator.

An experimental comparison of two different technetium source activities which can imitate thyroid scintigraphy in case of thyroid toxic nodule.

Purpose:In cases of thyroid toxic autonomous nodule, anterior projection of Tc-99m pertechnetate image shows a hot nodule that occupies most, or the entire thyroid lobe with near-total or total suppression of the contra lateral lobe. In this case is very difficult to distinguish toxic nodule from lobe agenesis. Our interest was to estimate and determinate the rate of radioactivity when the source with high activity can make total suppression of the second source with low activity in same conditions with thyroid scintigraphy procedures.Material and methodology:Thyroid scintigraphy was performed with Technetium 99 meta stable pertechnetate. A parallel high resolution low energy collimator was used as an energy setting of 140 KeV photo peak for T-99m. Images are acquired at 200 Kilo Counts in the anterior projection with the collimator positioned as close as the patient’s extended neck (approximately in distance of 18 cm). The scintigraphy of thyroid gland was performed 15 minutes after intravenous administration of 1.5 mCi Tc-99m pertechnetate. Technetium 99 meta stable radioactive sources with different activity were used for two scintigraphies studies, performed in same thyroid scintigraphy acquisition procedures. In the first study, were compared the standard source with high activity A=11.2 mCi with sources with variable activities B=1.33 mCi; 1.03 mCi; 0.7 mCi; 0.36 mCi; and 0.16mCi) in distance of 1.5cm from each other sources, which is approximately same with distance between two thyroid lobes. In the second study were compared the sources with low activity in proportion 70:1(source A = 1.5 mCi and source B=0.021mCi). As clinical studies we preferred two different patents with different thyroid disorders. There were one patient with thyroid toxic nodule in the right lobe, therefore the second patient was with left thyroid nodule agenesis.Results:During our examination, we accurately determined that two radioactive sources in proportion 70:1 will be displayed as only one source with complete suppression of other source with low radioactivity. Also we found that covering of toxic nodules with lead cover (plaque), can allow visualization of activity in suppressed lobe.Conclusion:Our study concluded that total lobe suppression, in cases of patients with thyroid toxic nodule, will happened for sure, if toxic nodule had accumulated seventy times more radioactivity than normal lobe. Also we concluded that covering of the toxic nodule with lead plaque, may permit the presentation of radioactivity in suppressed nodule.

Evaluation of dead-time corrections for post-radionuclide-therapy 177Lu quantitative imaging with low-energy high-resolution collimators

Dead-time (DT) effects rarely cause problems in diagnostic single-photon emission computed tomography (SPECT) studies; however, in post-radionuclide-therapy imaging, DT can be substantial. Therefore, corrections may be necessary if quantitative images are used in image-based dosimetry or for evaluation of therapy outcomes. This task is particularly challenging if low-energy collimators are used. Our goal was to design a simple method to determine the dead-time correction factor (DTCF) without the need for phantom experiments and complex calculations. Planar and SPECT/CT scans of a water phantom containing a 70 ml bottle filled with lutetium-177 (Lu) were acquired over 60 days. Two small Lu markers were used in all scans. The DTCF based on the ratio of observed to true count rates measured over the entire spectrum and using photopeak primary photons only was estimated for phantom (DT present) and marker (no DT) scans. In addition, variations in counts in SPECT projections (potentially caused by varying bremsstrahlung and scatter) were investigated. For count rates that were about two-fold higher than typically seen in post-therapy Lu scans, the maximum DTCF reached a level of about 17%. The DTCF values determined directly from the phantom experiments using the total energy spectrum and photopeak counts only were equal to 13 and 16%, respectively. They were closely matched by those from the proposed marker-based method, which uses only two energy windows and measures photopeak primary photons (15-17%). A simple, marker-based method allowing for determination of the DTCF in high-activity Lu imaging studies has been proposed and validated using phantom experiments.

A study on sensitivity correction factor of gamma camera in whole body bone image

The aim of this study was to calculate a reasonable correction factor that could be corrected when the sensitivity of each gamma camera is measured and a whole body bone scan is performed as a follow-up examination. Seven pieces of equipment were used to analyse the sensitivity measurements of each gamma camera based on the source sensitivity measurement method recommended by the IAEA. These were BRIGHTVIEW, PRECEDENCE, ECAM, ECAM signature, ECAM Plus, SYMBIA T2 and INFINIA. The 99mTc line source for the sensitivity measurement was generated in 4–7 kcps, which are the common values in a whole body bone scan. All the cameras were equipped with a low-energy and high-resolution parallel multi-hole collimator and set at a window width and photo peak of 15% and 140 keV, respectively. After placing the 99mTc source as closely as possible to the collimator, the count was measured for 60 and 120 seconds to calculate correction factor. To determine if the correction factor calculated using the 99mTc line source could be applied to a whole body bone scan of a real patient, a whole body bone scan was performed on 27 patients before applying the correction factor for comparative analysis. According to the experimental results using the 99mTc line source, the gamma camera sensitivity was the highest for ECAM plus, followed in order by the gamma cameras, ECAM signature, SYMBIA T2, ECAM, BRIGHTVIEW, INFINIA and PRECEDENCE. When the results were used to calculate the correction factor based on the ECAM gamma camera, which had a medium-degree of sensitivity, the respective correction factors were 1·07, 1·05, 1·03, 1·00, 0·90, 0·83 and 0·72. The correction factors calculated based on the experiment using a 99mTc line source were similar to those calculated based on the whole body bone scan. Clinical application of correction factor for measured sensitivity enables estimation of factor correction depending on difference in equipment when image is read, which improves accuracy and reliability of examination, and is expected to be used especially for continuous follow-up examination.

Evaluation of a matched filter resolution recovery reconstruction algorithm for SPECT-CT imaging

The aim of our study was to assess improvements in spatial resolution and noise control from the application of the Astonish resolution recovery algorithm for single photon emission computed tomography imaging. Secondary aims were to compare acquisitions made with low-energy general purpose collimators with those obtained using low-energy high-resolution collimators in this context and evaluate the potential of a finer matrix to improve image quality further. A Tc-filled Jaszczak phantom with hot spheres was used to assess contrast and noise. A National Electrical Manufacturers Association triple line source single photon emission computed tomography resolution phantom was used to measure spatial resolution. Acquisitions were made using both low-energy high-resolution and low-energy general purpose collimators. Compared with standard ordered subsets expectation maximization reconstructions, the resolution recovery algorithm resulted in a higher spatial resolution (8 vs. 14 mm full-width at half-maximum) leading to reduced partial volume effects in the smaller Jaszczak spheres. Higher image contrast was achieved alongside lower levels of noise. An edge enhancement artefact was observed in the resolution recovery corrected images. An overestimate of the target-to-background activity was also observed for the larger spheres. The use of such an algorithm results in images characterized by increased spatial resolution and reduced noise. However, small sources of the order of 2-3 cm can be significantly overenhanced.

Quantification of myocardial area at risk in the absence of collateral flow: The validation of angiographic scores by myocardial perfusion single-photon emission computed tomography

ObjectivesOur study aimed to compare the area at risk (AAR) determined by single-photon emission computed tomography (SPECT) with the Bypass Angioplasty Revascularization Investigation (BARI) and modified Alberta Provincial Project for Outcome Assessment in Coronary Heart Disease (APPROACH) angiographic scores in the setting of patients undergoing coronary angioplasty for either unstable angina or an STEMI. BackgroundRadionuclide myocardial perfusion imaging prior to reperfusion has classically been the most widely practised technique for assessing the AAR and has been successfully used to compare the efficacy of various reperfusion strategies in patients with an ST-segment elevation myocardial infarction (STEMI). The BARI and modified APPROACH scores are angiographic methods widely used to provide a rapid estimation of the AAR; however, they have not been directly validated with myocardial perfusion single-photon emission computed tomography (SPECT). MethodsFifty-five patients with no previous myocardial infarction who underwent coronary angioplasty for single-vessel disease (unstable angina: n = 25 or an STEMI: n = 30) with no evidence of collaterals (Rentrop Collateral Score <2) were included in a prospective study. In STEMI patients, the 99mTc-tetrofosmin was injected prior to opening of the occluded vessel and, in patients with unstable angina after 10-15 seconds of balloon inflation. Acquisition was performed with a dual-head gammacamera with a low-energy and high-resolution collimator. A total of 60 projections were acquired using a non-circular orbit. No attenuation or scatter correction was used. Maximal contours of hypoperfusion regions corresponding to each coronary artery occlusion were delineated over a polar map of 17 segments and compared with the estimated AAR determined by two experienced interventional cardiologists using both angiographic scores. ResultsMean AAR percentage in SPECT was 35.0 (10.0%-56.0%). A high correlation was found between BARI and APPROACH scores (r= 0.9, P< .001). Furthermore, a high correlation was also observed between BARI versus SPECT and APPROACH versus SPECT to estimate the AAR (r= 0.9, P< .001 and r= 0.8, P< .001, respectively). Better correlations were observed when the left anterior descending artery (LAD) was revascularized (r= 0.8, P< 0.001 with BARI; r= 0.8, P= .001 with APPROACH) compared to other territories (r= 0.8, P= .001 with BARI; r= 0.7, P= .001 with APPROACH). Also, better correlations were observed in patients who underwent an elective rather than a primary percutaneous revascularization procedure. ConclusionsIn the absence of collateral flow, BARI and APPROACH scores constitute valid methods for AAR estimation in current clinical practice, with more accurate results when used for the LAD territory; both are useful not only in STEMI patients but also in patients with unstable angina.

The effect of type of filters and collimators on the SPECT axis of rotation error

High resolution and artifact free SPECT reconstruction of the distribution of radioactive sources over the entire imaging field requires exact alignment between the electronic and the mechanical axis of rotations. In this paper, the effect of misalignment between the electronic and the mechanical axis of rotations of SPECT system equipped with low-energy high-resolution and low-energy general-purpose collimators through the field of view has been studied. In addition, the useful dimensions of the SPECT field of view without artifact due to axis of rotation error have been calculated. Furthermore, the roles of digital filters in reducing this effect have been studied.

Primary intrathoracic goiter: Incidental diagnosis on 99m-Tc pertechnetate radioisotope thyroid scan

Primary intrathoracic goiter: Incidental diagnosis on 99m-Tc pertechnetate radioisotope thyroid scan

Evaluation of Regional Brain Perfusion in Patients with Pseudoexfoliation Syndrome

Pseudoexfoliation syndrome (PES) is characterised by the accumulation of abnormal extracellular fibrillar material in ocular tissue, which develops with ageing, and can lead to ocular complications, including glaucoma, cataract, zonular damage, and keratopathy. It has been shown that extraocular accumulation of pseudoexfoliation matter can occur in tissues such as the heart, lung, liver, kidney, cerebral meninges, aorta, and adventitia layer of cerebral arteries. Acute vascular complications are seen commonly with the involvement of the systemic vasculature. Pseudoexfoliation syndrome has also been reported in dementia and stroke patients. In this study, the authors aimed to evaluate regional brain perfusion in pseudoexfoliation syndrome patients. Twenty-four patients with PES with glaucoma (14 female, 10 male) and a control group of 19 healthy volunteers (10 female, 9 male) were included in the study. There was no cerebrovascular or psychiatric complaint in the patient or control group, and all subjects were right-handed. Brain perfusion single-photon emission computed tomography (SPECT) images were taken by low-energy general purpose collimator of a single-headed gamma camera after intravenous injection of 25 mCi technetium-99m-hexamethylpropylene amine oxime (Tc99m-HMPAO). To obtain the corticocerebellar ratio by semiquantitative analysis, 3 × 3 pixel regions of interest were drawn on transaxial sections, and the counts of frontal, temporal, parietal, and occipital regions were divided by the counts of the cerebellar region bilaterally. The mean ages of the PES and control groups were 67.83 ± 9.03 and 64.52 ± 6.88 years, respectively. The mean corticocerebellar ratio in PES was decreased in frontal, temporal, parietal, and occipital lobes bilaterally (p value interval min: 0.001, max: 0.049). The results showed that there was a decrease in frontal, temporal, parietal, and occipital cortices perfusion in PES patients bilaterally.

Standardization of metaiodobenzylguanidine heart to mediastinum ratio using a calibration phantom: effects of correction on normal databases and a multicentre study

This study was performed to demonstrate that the results obtained with a calibration phantom could be used as a tool for standardizing measurement of heart to mediastinum (H/M) ratio in cardiac metaiodobenzylguanidine (MIBG) imaging. Images of the phantom containing (123)I-MIBG were acquired on the cameras in 10 hospitals (11 camera types) to determine the relationship between H/M ratios using different collimators: low-energy (LE) and medium-energy (ME)/low-medium-energy (LME) collimators. The effect of standardization on the ME-comparable H/M ratio was examined in two settings: a Japanese standard MIBG database (n = 62) and multicentre studies (n = 49). In a multicentre study, probable Alzheimer's disease (AD, n = 18) and probable dementia with Lewy bodies (DLB, n = 31) were studied and standardized by the calibration phantom method. Linear regression equations between LE and ME collimators were obtained for the phantom study in all institutions. When the H/M ratio with an LE collimator was corrected based upon the calibration phantom, the corrected values were comparable to those obtained using ME collimators. The standard database also exhibited a normal distribution after standardization as determined by skewness and goodness-of-fit test. A mixture of the populations by LE and ME collimators showed significant separation of AD and DLB groups (F ratio = 24.9 for the late H/M), but the corrected values resulted in higher F ratios for both early and late H/M (F ratio = 34.9 for the late H/M). Standardization of H/M ratios by the heart-chest calibration phantom method is feasible among different collimator types. This method could be practically used for multicentre comparison of H/M ratios.

Comparison of Pinhole and High-Resolution Parallel-Hole Imaging for Nodular Thyroid Disease

Pinhole has been the main standard collimator to be used for thyroid imaging. There has been a gradually increasing trend to replace pinhole with the use of high-resolution low-energy parallel-hole collimator with zoom in thyroid imaging. The objective of this study is to compare parallel-hole collimator acquisition of thyroid gland with that obtained by pinhole collimator to find the effect on the diagnostic information in nodular thyroid disease. A total of 29 patients, 24 women and 5 men, aged 18 to 70 years who were routinely referred for thyroid imaging for the assessment of nodular disease were studied. Each patient was injected with 185 MBq (5 mCi) of Tc-99m sodium pertechnetate intravenously. After 20 minutes, acquisition using pinhole followed by parallel-hole collimators was obtained. For pinhole acquisition, a 3-mm insert was used, and 3 images were obtained in the anterior and anterior oblique projections. For parallel-hole acquisition, anterior view was obtained for 250 K. The collimator was placed as close as possible to the patient. The image quality, number, and definition of nodules were evaluated by 2 independent, qualified nuclear medicine physicians. Differences were resolved by consensus. There were 14 patients who had nodular patterns and 15 had no apparent nodules. There were 40 nodules of different sizes detected by pinhole imaging. Only 10 (25%) of these nodules were observed on parallel-hole images. Pinhole imaging must be used for thyroid imaging particularly in patients suspected of having nodular disease.

Evaluation of dual γ-ray imager with active collimator using various types of scintillators

The performance of a specialized dual γ-ray imager using both mechanical and electronic collimation was evaluated by Monte Carlo simulation (MCNP5). The dual imager consisted of an active collimator and a planar detector that were made from scintillators. The active collimator served not only as a coded aperture for mechanical collimation but also as a first detector for electronic collimation. Therefore, a single system contained both mechanical and electronic collimation. Various types of scintillators were tested and compared with each other in terms of their angular resolution, efficiency, and background noise. In general, a BGO active collimator had the best mechanical collimation performance, and an LaCl 3(Ce) active collimator provided the best electronic collimation performance. However, for low radiation energies, the mechanical collimation images made from both scintillators showed the same quality, and, for high radiation energies, electronic collimation images made from both scintillators also show similar quality. Therefore, if mechanical collimation is used to detect low-energy radiation and electronic collimation is applied to reconstruct a high-energy source, either LaCl 3(Ce) or BGO would be appropriate for the active collimator of a dual γ-ray imager. These results broaden the choice of scintillators for the active collimator of the dual γ-ray imager, which makes it possible to consider other factors, such as machinability and cost, in making the imager. As a planar detector, BGO showed better performance than other scintillators since its radiation detection efficiency was highest of all.

Improved Quality of Pediatric 123I-MIBG Images with Medium-Energy Collimators

Our objective was to optimize the quality of (123)I-metaiodobenzylguanidine (MIBG) scans by using a medium-energy collimator to reduce high-energy-photon septal penetration. In addition to the 159-keV γ-ray, (123)I has a small abundance of energies above 400 keV that can compromise the image quality of MIBG studies because of septal penetration. Using a low-energy ultrahigh-resolution collimator (LEUHR), a low-energy high-resolution collimator (LEHR), and a medium-energy collimator, we obtained and compared SPECT and planar images of a SPECT phantom filled with (123)I. These studies were acquired at a count level comparable to clinical MIBG images, 24,000 counts per view for SPECT and 300,000 counts for planar imaging. Also, we evaluated the sensitivity of the 3 collimators at 0 and 10 cm using the National Electrical Manufacturers Association protocol. The image quality for both SPECT and planar (123)I images using the medium-energy collimator was determined to be substantially better than that using the LEUHR or LEHR collimator. The septa of the medium-energy collimator are thicker than those of the low-energy collimators (1.14 vs. 0.13-0.16 mm), leading to a significant reduction in septal penetration of the high-energy γ-rays and a marked improvement in image quality. The sensitivity for the medium-energy collimator did not change with distance (8.00 cpm/kBq), as opposed to the LEUHR collimator (6.59 and 5.51 cpm/kBq for 0 and 10 cm, respectively) and the LEHR collimator (14.32 and 12.30 cpm/kBq for 0 and 10 cm, respectively). This variation in sensitivity for the LEUHR collimator is again due to the presence of high-energy photons. Use of a medium-energy collimator substantially improves the quality of both planar and SPECT (123)I images. We recommend that a medium-energy collimator routinely be used for (123)I-MIBG imaging.

Technetium-99m-hexamethylpropylene amine oxime lung scintigraphy findings in patients with Behçet's disease

Behçet's disease (BD) is a multisystem disorder that is characterized by vasculitis, and consists of a triad of recurrent ulcers of the oral and genital mucosa with relapsing uveitis. The prevalence of pulmonary involvement varies in the range of 1-10% in various studies, and its complications are severe and life threatening. To objectively assess the degree of pulmonary vascular endothelial damage in BD, the lung uptake, and the clearance rate of technetium-99m-hexamethylpropylene amine oxime (Tc-99m-HMPAO) were determined. Twenty-three nonsmoking patients with BD (10 female, 13 male) and 11 (six female, five male) healthy nonsmoking controls underwent Tc-99m-HMPAO lung scanning, pulmonary function tests (PFT), chest radiograph examination, contrast-enhanced spiral chest computed tomography scanning, and high-resolution computed tomography examinations. Immediately after the bolus injection of 740 MBq of Tc-99m-HMPAO posterior sequential images were obtained at 1-s intervals for 150 s and subsequent images were obtained at one frame per minute (min) over a 10-min period, using a double-headed gamma camera equipped with a low-energy all-purpose parallel hole collimator. Dynamic images were used to calculate the Tc-99m-HMPAO lung clearance rate (T1/2). Simultaneously, a static anterior image, including a large part of the liver, was obtained of 5-min duration at 10 min after the injection. Regular regions of interests were drawn over the midportion of the right lung and the highest activity area of the liver parenchyma was selected and lung/liver (L/Li) uptake ratios were calculated to represent the degree of pulmonary vascular endothelial damage. Chest radiograph, high-resolution computed tomography, and computed tomography findings in patients with BD were nonspecific for BD. There was also a statistically significant difference between patients with BD (30.26 ± 10.55 s) and normal controls (19.53 ± 6.24 s) on their T1/2 values (P = 0.0004). The results show that the L/Li ratios on the Tc-99m-HMPAO lung scan were significantly higher in patients with BD (0.60 ± 0.19) than those in normal controls (0.39 ± 0.07) (P = 0.0021). Using a cutoff value of 0.50, 15 of 23 (65%) patients with BD had increased L/Li ratios. No correlation was found between the mean T1/2 values of Tc-99m-HMPAO clearance and the PFT in patients with BD. The L/Li ratios were not correlated with PFT in patients with BD. The degree of pulmonary vascular endothelial damage was represented as increased L/Li ratios and decreased lung clearance rate measured on the Tc-99m-HMPAO lung scan in patients with BD. Our results indicated that determining the T1/2 values and the L/Li ratios on Tc-99m-HMPAO lung imaging should be an objective method to assess subclinical pulmonary damage even in the early stages of BD in the patients.

SPECT Imaging for Brain Improvement Quantification in a Patient With Cerebrotendinous Xanthomatosis

Cerebrotendinous xanthomatosis is a rare recessive autosomal disease caused by mutations of the sterol 27-hydroxylase gene (CYP27), which leads to reduced synthesis of bile acids, particularly chenodeoxycholic acid (Cali et al, J Biol Chem. 1991;266:7779-7783; Gallus et al, Neurol Sci. 2006;27:143-149). The disease is characterized by progressive neurologic dysfunction due to accumulation of cholestanol in neurologic tissues (Moghadasian et al, Arch Neurol. 2002;59:527-529; Selva-O'Callaghan et al, Rheumatology. 2007;46:1212-1213). Long-term treatment with chenodeoxycholic acid can arrest or even reverse progression of the disease (Pierre et al, J Inherit Metab Dis. In press).Brain SPECT with 740 MBq of Tc-99m ethyl cysteinate dimmer, using a double-head gamma camera (Siemens E.cam) with high-resolution, low-energy parallel collimators was performed in our patient at onset and 2 years after starting chenodeoxycholic acid treatment. SPECT acquisitions were performed using a 360-degree orbit, 1 image/30 seg/3 degree, and 128 × 128 matrix. Reconstruction was by means of filtered back-projection, Butterworth 5/0.25, without attenuation correction. Pre- and post-SPECT dicom images were reoriented into Talairach space using NeuroGam (Segami Corporation). To visually identify abnormal perfusion regions, volume render brain image was computed, where abnormal perfusion regions were found by comparing with age-matched normal database, and Brodmann areas (BA) were quantified. Pre- versus post-treatment changes were computed by means of relative percentage between counts. Post-treatment SPECT showed better perfusion than pretreatment SPECT with an increase between 5% and 10% in frontal cortex (BA 9, BA 24, BA 32, BA 46, BA 47), parietal cortex (BA 5, BA 31), and temporal cortex (BA 20, BA 22, BA 28, BA 36, BA 37, BA 38), and with an increase of more than 10% in frontal cortex (BA 45) and parietal cortex (BA 23). This case illustrates the benefit of bile acid therapy for halting and even reversing neurologic retardation in this condition.

Multiple Modality $\gamma$-Ray Imager Using LaCl$_{3}$(Ce) Scintillators With Active Collimation Method

Multiple modality γ-ray imaging using mechanical and electronic collimation with different detection methods was proposed and tested by simulation. Although conventional mechanical collimators, which are made from high atomic number and density materials, passively filter the incident radiation, the mechanical collimator reported in this study consisted of LaCl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (Ce) scintillators, which actively collimate the radiation and are used as the 1st detector of an electronic collimator to reconstruct a Compton image. A detector box made from six planar LaCl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (Ce) scintillators was positioned behind the active collimator. The LaCl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (Ce) scintillator arrays used as the active collimator and box detector consisted of voxels, each 2 mm × 2 mm × 5 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> in size. A combination of active collimators and box detectors can produce multiple modalities for both mechanical and electronic collimation. The information from each modality was combined effectively using the maximum likelihood expectation maximization (MLEM) method. Therefore, a reconstructed image from multiple modalities has inherently higher efficiency than each conventional modality. The reconstructed images were evaluated using the resolution-variance curve as a quantitative method. Although mechanical collimation is effective at low γ-ray energy and electronic collimation shows high performance at high γ-ray energy, multiple modalities are superior to the conventional single modalities for intermediate γ-ray energies (364 keV). The angular resolution and absolute efficiency were calculated for each modality and source energy.

Intradermal lymphoscintigraphy at rest and after exercise: a new technique for the functional assessment of the lymphatic system in patients with lymphoedema

The aim of this study was to evaluate the effect of implementing a new technique, intradermal injection lymphoscintigraphy, at rest and after muscular exercise on the functional assessment of the lymphatic system in a group of patients with delayed or absent lymph drainage. We selected 44 patients (32 women and 12 men; 15 of 44 with upper limb and 29 of 44 with lower limb lymphoedema). Thirty of 44 patients had bilateral limb lymphoedema and 14 of 44 had unilateral disease; 14 contralateral normal limbs were used as controls. Twenty-three patients had secondary lymphoedema after lymphadenectomy and the remaining 21 had idiopathic lymphoedema. Each of the 44 patients was injected with 50 MBq (0.3-0.4 ml) of (99m)Tc-albumin-nanocolloid, which was administered intradermally at the first interdigital space of the affected limb. Two planar static scans were performed using a low-energy general-purpose collimator (acquisition matrix 128 x 128, anterior and posterior views for 5 min), and in which drainage was slow or absent, patients were asked to walk or exercise for 2 min. A postexercise scan was then performed to monitor and record the tracer pathway and the tracer appearance time (TAT) in the inguinal or axillary lymph nodes. The postexercise scans showed that (i) 21 limbs (15 lower and six upper limbs) had accelerated tracer drainage and tracer uptake in the inguinal and/or axillary lymph nodes. Two-thirds of these showed lymph stagnation points; (ii) 27 limbs had collateral lymph drainage pathways; (iii) in 11 limbs, there was lymph drainage into the deeper lymphatic channels, with unusual uptake in the popliteal or antecubital lymph nodes; (iv) six limbs had dermal backflow; (v) three limbs did not show lymph drainage (TAT=not applicable). TAT=15 + or - 3 min, ranging from 12 to 32 min in limbs with lymphoedema versus 5 + or - 2 min, ranging from 1 to 12 min in the contralateral normal limbs (P<0.001). Intradermal injection lymphoscintigraphy gives a better imaging of the lymph drainage pathways in a shorter time, including cases with advanced lymphoedema. In some patients with lymphoedema, a 2-min exercise can accelerate tracer drainage, showing several compensatory mechanisms of lymph drainage. The effect of the exercise technique on TAT and lymphoscintigraphy findings could result in a more accurate functional assessment of lymphoedema patients.

PTH-032 Scintigraphic gastric emptying: clinical impression vs outcome

<h3>Introduction</h3> In patients presenting with upper gastrointestinal (GI) symptoms, clinical impression of rapid or delayed gastric emptying (GE) may be misleading. This study was undertaken to determine the frequency of rapid/delayed GE compared to clinical presentation in patients referred for GE scintigraphy. <h3>Methods</h3> A retrospective review of 642 (234 males, 408 females, mean age 45 years old) consecutive GE studies was performed. Each patient received a standard solid meal containing two large eggs labelled with 12 MBq of 99mTc-tin colloid and a glass of water. Static imaging in upright position (anterior and posterior 60 s) every 15 min was performed for 150 min using a large field of view gamma camera fitted with a low energy collimator and a computer system. GE was classified as normal, rapid and delayed based on half-emptying time and percentage retained at 150 min. <h3>Results</h3> Seventy (11%) patients with suspected rapid and 572 (89%) with suspected delayed GE were studied. Normal, rapid and delayed GE, respectively, were observed in 11 (16%), 54 (77%) and 5 (7%) patients with the clinical suspicion of rapid GE and 178 (31%), 215 (37%) and 178 (31%) patients with suspected delay in GE. One patient with suspected delay had a biphasic GE pattern. Positive Predictive Value (PPV) of clinical suspicion for rapid GE was 77% while PPV of clinical suspicion for delayed GE was 31%. <h3>Conclusion</h3> Our experience demonstrates that clinical impression is often an unreliable predictor of the outcome of GE scintigraphy, especially in patients suspected of having a delayed GE. GE scintigraphy using solid egg meal is a very useful investigation in the management of patients presenting with complex upper GI symptoms.