Rotating Gamma Camera Research Articles

Monte Carlo Simulation and Reconstruction: Assessment of Myocardial Perfusion Imaging of Tracer Dynamics With Cardiac Motion Due to Deformation and Respiration Using Gamma Camera With Continuous Acquisition.

PurposeMyocardial perfusion imaging (MPI) with single photon emission computed tomography (SPECT) is routinely used for stress testing in nuclear medicine. Recently, our group extended its potential going from 3D visual qualitative image analysis to 4D spatiotemporal reconstruction of dynamically acquired data to capture the time variation of the radiotracer concentration and the estimated myocardial blood flow (MBF) and coronary flow reserve (CFR). However, the quality of reconstructed image is compromised due to cardiac deformation and respiration. The work presented here develops an algorithm that reconstructs the dynamic sequence of separate respiratory and cardiac phases and evaluates the algorithm with data simulated with a Monte Carlo simulation for the continuous image acquisition and processing with a slowly rotating SPECT camera.MethodsA clinically realistic Monte Carlo (MC) simulation is developed using the 4D Extended Cardiac Torso (XCAT) digital phantom with respiratory and cardiac motion to model continuous data acquisition of dynamic cardiac SPECT with slowly rotating gamma cameras by incorporating deformation and displacement of the myocardium due to cardiac and respiratory motion. We extended our previously developed 4D maximum-likelihood expectation-maximization (MLEM) reconstruction algorithm for a data set binned from a continuous list mode (LM) simulation with cardiac and respiratory information. Our spatiotemporal image reconstruction uses splines to explicitly model the temporal change of the tracer for each cardiac and respiratory gate that delineates the myocardial spatial position as the tracer washes in and out. Unlike in a fully list-mode data acquisition and reconstruction the accumulated photons are binned over a specific but very short time interval corresponding to each cardiac and respiratory gate. Reconstruction results are presented showing the dynamics of the tracer in the myocardium as it continuously deforms. These results are then compared with the conventional 4D spatiotemporal reconstruction method that models only the temporal changes of the tracer activity. Mean Stabilized Activity (MSA), signal to noise ratio (SNR) and Bias for the myocardium activities for three different target-to-background ratios (TBRs) are evaluated. Dynamic quantitative indices such as wash-in (K1) and wash-out (k2) rates at each gate were also estimated.ResultsThe MSA and SNR are higher with higher TBRs while biases were improved with higher TBRs to less than 10%. The correlation between exhalation-inhalation sequence with the ground truth during respiratory cycle was excellent. Our reconstruction method showed better resolved myocardial walls during diastole to systole as compared to the ungated 4D image. Estimated values of K1 and k2 were also consistent with the ground truth.ConclusionThe continuous image acquisition for dynamic scan using conventional two-head gamma cameras can provide valuable information for MPI. Our study demonstrated the viability of using a continuous image acquisition method on a widely used clinical two-head SPECT system. Our reconstruction method showed better resolved myocardial walls during diastole to systole as compared to the ungated 4D image. Precise implementation of reconstruction algorithms, better segmentation techniques by generating images of different tissue types and background activity would improve the feasibility of the method in real clinical environment.

Prognostic Value of Single-Photon Emission Computed Tomography of Left Ventricular Synchronized with ECG for Cardiotoxicity Assessment in Patients with Malignant Lymphoma after High Dose Chemotherapy with Autologous Stem Cell Transplantation

Introduction: High-dose chemotherapy (HDC) with autologous hematopoietic stem cells transplantation (auto-HSCT) is currently widely used for the treatment of relapsed and refractory to standard chemotherapy cases of malignant lymphomas. Examination of patients for evaluation cardiotoxic effect of HDC and auto-HSCT is usually performed with an electrocardiography and echocardiography. The method of single photon emission computed tomography of the left ventricular(LV) myocardium, synchronized with the patient's ECG (Gated - SPECT) is rarely used to assess cardiotoxic effect of HDC and auto-HSCT, and its prognostic value in this field is not determined.Objective: to evaluate perfusion and regional myocardial function of the left ventricle (LV) using Gated-SPECT in malignant lymphomas patients receiving HDC and auto-HSCT. To evaluate whether the age and conditioning regimens influence the worsening of indices of hyperperfusion according to Gated-SPECT.Materials and methods: The study included 127 patients (67 with Hodgkin's lymphoma, 28 with non-Hodgkin's lymphoma, 32 with multiple myeloma). The median age was 37 year (range: 19 to 68 years); 80 females, 47 males. Gated-SPECT was used for assessment of perfusion and regional left ventricular function at rest before the HDC and auto-HSCT (point 1) and at discharge (point 2). The each study was performed on a double-headed rotating gamma camera «Forte» (Philips, USA) after intravenous injection of 740 MBq of technetium-99m-methoxyisobutylisonitrile (99mTc-MIBI). Gated-SPECT was used to measure the conventional parameters (total hypoperfusion defect, total LVEF) and also to measure regional myocardial perfusion and thickening used the 20-segment “bull's eye” model (the LV myocardium was divided into 20 segments).Results: The total area of hypoperfusion, expressed as a percentage of the area of the left ventricular myocardial wall did not change significantly during treatment (p> 0,05). However, segmental analysis of regional myocardial perfusion has revealed a statistically significant decrease in the median level uptake of the 99mTc-MIBI in 1,2,3,4,5,6,7,8,9,10,11,13,14,16,17,19,20 segments (p =0,01). The total ejection fraction (TEF) decreased, but change was not significant (median TEF at point 1 was 60,4 %, at point 2 - 59,9 %). But it showed a statistically significant decrease in median of local systolic thickening in 2,3,4,5,6,8,9,11,12,14,15,18,19,20 segments (p <0,05).It was also found that there was no correlation in the age of patients with hypoperfusion changes in the time of admission, but after treatment there was a direct significant weak correlation between these indices (R = 0.22, p = 0.01), So, older patient patient, have the greater size of the general hypoperfusion zone (Table 1).The analysis showed that the conditioning regimen (BEAM, high doses of melphalan or CBV) did not affect the index of the general hypoperfusion zone, which was established when comparing the parameters between pairs: ВЕАМ and high doses of melphalan, ВЕАМ and CBV, CBV and high doses of melphalan. Significant changes of general hypoperfusion zone were not detected when compare this indices at the time patients was admitted to the hospital with indices at the time of discharge from the hospital, that is, after HDC and auto-HSCTConclusions:HDC and auto-HSCT significantly change perfusion and regional LV myocardial function in patients with malignant lymphomas. Changes revealed evidence of diffuse myocardial damage. There was no difference in general hypoperfusion zone between different conditioning regimen before and after the treatment. Gated-SPECT can be considered as a promising method for assessing cardiac HDC and auto-HSCT. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

The origins of SPECT and SPECT/CT

Single photon emission computed tomography (SPECT) has a long history of development since its initial demonstration by Kuhl and Edwards in 1963. Although clinical utility has been dominated by the rotating gamma camera, there have been many technological innovations with the recent popularity of organ-specific dedicated SPECT systems. The combination of SPECT and CT evolved from early transmission techniques used for attenuation correction with the initial commercial systems predating the release of PET/CT. The development and acceptance of SPECT/CT has been relatively slow with continuing debate as to what cost/performance ratio is justified. Increasingly, fully diagnostic CT is combined with SPECT so as to facilitate optimal clinical utility.

Motion-tracking technique in unrestrained small-animal single-photon emission computed tomography

Medical researchers have used structural and functional imaging techniques to study various neurological phenomena. Humans are typically conscious for both structural and functional neuroimaging studies. The use of functional neuro-imaging techniques in mouse-based animal models is typically accomplished with restrained or anesthetized mice. A system was developed to perform functional imaging with single-photon emission computed tomography of awake mice to avoid the confounding influences of anesthesia or physical restraint. This review article provides an overview of the technique and how it is presently being used. The system is designed for brain imaging and uses infrared reflectors to track the head position as a function of time. The detected photons are acquired in list mode and are time-stamped. The position of the rotating gamma camera is also recorded as a function of time. These three sets of data are integrated together in an iterative image reconstruction program that performs motion compensation. The successful performance of the system is demonstrated in moving phantom and awake animal studies. The system and methodology has the potential of being a powerful tool in behavioral neuroimaging studies involving awake, unrestrained mice.

New SPECT technology: potential and challenges

The article by Bocher et al. in this issue [1] reports on the performance of a novel SPECT system specifically designed for cardiac imaging based on the use of a set of pinhole collimators in combination with cadmium zinc telluride (CZT) detectors. The system is inspired by earlier work on multipinhole imaging [2] and the conceptual design has previously been demonstrated in simulation studies [3]. Also early clinical validation studies have appeared recently [4, 5]. The described system (available from GE Healthcare) joins a range of novel organ-specific commercial systems that have recently been introduced to the consumer with reported improvement in resolution and sensitivity (usually reported as potential for reduced acquisition time; see recent reviews [6, 7]). Specific examples are the D-SPECT from Spectrum Dynamics [8, 9] and the Cardius from Digirad [10]. Clinical validation studies for these systems are now also appearing (e.g. [11, 12]). The developers of these systems deserve congratulations for introducing innovations that undoubtedly yield the largest advance in SPECT performance since the introduction of the rotating gamma camera, which has dominated clinical use for several decades. Until recently the development in SPECT performance has been incremental, mainly involving refinement rather than major changes in system design, perhaps mainly due to the clinical demand for systems that offer flexibility in application. The recent innovation has been inspired at least partly by the rapid developments in preclinical imaging systems where ultrahigh resolution and relatively high sensitivity have been demonstrated. Bringing new designs to fruition has only been possible due to the combination of several factors: the improved reliability of alternative detector materials, the development of fast electronics, the development of efficient reconstruction algorithms and, not least, the demand for organ-specific systems where optimization for a specific purpose rather than flexibility in application is indicated.

Perturbative Refinement of the Geometric Calibration in Pinhole SPECT

The paper investigates the geometric calibration of a rotating gamma camera for pinhole (PH) single photon emission computed tomography (SPECT) imaging. Most calibration methods previously applied in PH-SPECT assume that the motion of the camera around the object belongs to a well-defined class described by a small number of geometric parameters, for instance seven parameters for a circular acquisition with a single pinhole camera. The proposed new method refines an initial parametric calibration by applying to each position of the camera a rigid body transformation that is determined to improve the fit between the measured and calculated projections of the calibration sources. A stable estimate of this transformation can be obtained with only three calibration sources by linearizing the equations around the position estimated by the initial parametric calibration. The performance of the method is illustrated using simulated and measured micro-SPECT data.

Effect of linearization correction on statistical parametric mapping (SPM): A99mTc-HMPAO brain perfusion SPECT study in mild Alzheimer’s disease

Statistical parametric mapping (SPM) was employed to investigate the regional decline in cerebral blood flow (rCBF) as measured by 99mTc-hexamethyl propylene amine oxime (HMPAO) single photon emission computed tomography (SPECT) in mild Alzheimer's disease (AD). However, the role of the post reconstruction image processing on the interpretation of SPM, which detects rCBF pattern, has not been precisely studied. We performed 99mTc-HMPAO SPECT in mild AD patients and analyzed the effect of linearization correction for washout of the tracer on the detectability of abnormal perfusion. Eleven mild AD (NINCDS-ADRDA, male/female, 5/6; mean+/-SD age, 70.6+/-6.2 years; mean+/-SD mini-mental state examination score, 23.9+/-3.41; clinical dementia rating score, 1) and eleven normal control subjects (male/female, 4/7; mean+/-SD age, 66.8+/-8.4 years) were enrolled in this study. 99mTc-HMPAO SPECT was performed with a four-head rotating gamma camera. We employed linearization uncorrected (LU) and linearization corrected (LC) images for the patients and controls. The pattern of hypoperfusion in mild AD on LU and LC images was detected by SPM99 applying the same image standardization and analytical parameters. A statistical inter image-group analysis (LU vs. LC) was also performed. Clear differences were observed between the interpretation of SPM with LU and LC images. Significant hypoperfusion in mild AD was found on the LU images in the left posterior cingulate gyrus, right precuneus, left hippocampus, left uncus, and left superior temporal gyrus (cluster level, corrected p < 0.005). With the LC images, significant hypoperfusion in AD was found only in the bilateral posterior cingulate gyrus and left precuneus (cluster level, corrected p < 0.005). A pattern of greater rCBF distribution at the high flow cortices and low flow cortices was observed on LC and LU images, respectively, in the case of both controls and mild AD patients. Hippocampal hypoperfusion could be detected by means of SPM in the LU images but not in the LC images. The results of SPM may vary in 99mTc-HMPAO SPECT with or without linearization correction, which should be carefully evaluated when interpreting the pattern of rCBF changes in mild Alzheimer's disease.

99mTc-labelled red blood cell single-photon emission computed tomography for the diagnosis and follow-up of juvenile nasopharyngeal angiofibroma*

To confirm the usefulness of blood pool scintigraphy with Tc-labelled red blood cells ((99m)Tc-RBCs) in the diagnosis and follow-up of juvenile nasopharyngeal angiofibroma. A prospective study design was used. (99m)Tc-RBCs were prepared by a modified in-vivo method. After the rapid intravenous injection of 370-740 MBq of (99m)Tc-RBCs, dynamic imaging of 1-min duration was performed. After dynamic imaging, static acquisitions at 5 min (second phase: blood pool phase) and 2 h (third phase: static image) were obtained. In addition, single-photon emission computed tomography (SPECT) imaging was performed at 2 h. SPECT images were obtained using a rotating gamma camera (GE-Starcam 4000 XR/T). All patients showed no activity in the first phase and mild activity in the second phase (blood pool phase). All patients with juvenile nasopharyngeal angiofibroma showed a prominent increased activity in the third phase and in SPECT images. This study shows that blood pool scintigraphy with (99m)Tc-RBC SPECT is very accurate, easy to perform and a suitable alternative to pre-operative and post-operative imaging techniques, including computed tomography scan, magnetic resonance imaging (MRI) and MRI angiography, for the detection of juvenile nasopharyngeal angiofibroma.

CBF imaging and global CBF quantification in normal rats using dedicated pinhole SPECT system

This work is intended to evaluate [99mTc]-radiolabeled pharmaceuticals for brain perfusion measurements in rats using pinhole SPECT. Our experiments aim to obtain quantitative data in normal animals. A dedicated Anger type rotating gamma camera (field of view 170 mm 170 mm, 25 photomultiplicators) was used with 1.5 mm hole diameter's pinhole collimator (Gaede Medizinsysteme Gmbh, Freiburg, Germany). 15 to 20 mCi of [99mTc]-hexamethyl propylamine oxime (Amersham Health, Little Chalfont, UK), was administered to 10 Wistar adult rats under general gaseous anesthesia (isoflurane 2%), through intravenous femoral catheter. During tracer administration, 120 planar images of 0.5 s were recorded. Ten minutes after, 48 projections of 1 min were acquired over a 180 dorsal arc. A specific cone beam algebraic reconstruction algorithm, taking into account distorsion of projection through pinhole, was employed leading to reconstructed voxel's sizes of 0.34 mm3. Micro-CT (eXplore LOCUS, General Electric Medical Systems, London, Canada) images of the same animal were fused with SPECT data for anatomical registration. Using the Patlak formalism, modified by Matsuda, we calculate global CBF values for each cerebral hemisphere. Images' contrast reflects normal tracer's uptake in the different cerebral territories. Signal to noise ratios in human and rat brain perfusion's images are comparable. Calculation leads to a gCBF of 110.1 ml/100g/min 11.4 value in the range of reference data. This technique could be used to assess CBF in pathological conditions in rats.

A computerized human reference brain for rCBF/SPET technetium-99m exametazime (HMPAO) investigation of elderly.

Using the bull's eye approach, a reference brain from the single photon emission tomography (SPET) images of 10 subjects aged 62-81 years with excellent mental and physical health was constructed. SPET images were acquired twice, 1 week apart, using a single detector rotating gamma camera collecting 64 planar images over a 360 degrees orbit. The centre of each transaxial slice was first defined with an automatic edge detecting algorithm applied to an anterior-posterior and a side profile of the brain. Each slice was divided into 40 sectors. Maximum counts/pixel in each sector was picked. The 40 maximum count values from one transaxial slice were allowed to form a horizontal row in a new parametric image on the x-axis and slice number from the vertex to the basal parts of the brain on the y-axis. This new image was scaled to a 64 x 16 pixel matrix by interpolation, which meant a normalization of all studies to the same size. The parametric image in each subject was scaled with regard to intensity by a factor calculated by a normalization procedure using the least squares analysis. Mean and SD for each pixel were calculated, thereby constructing a "mean parametric image", and a "SD parametric image". These two images are meant to be used as the reference brain for evaluation of patient studies. This method can be used for objective measurements of diffuse brain changes and for pattern recognition in larger groups of patients. Statistical multifactorial analysis of parameters used for acquisition and data processing is possible.

An ultra-high-energy collimator for small animal imaging in dual-isotope study of 18F and 99mTc

We have developed a pinhole collimator for small animal imaging using dual-isotopes, such as gamma and positron emitters. A lead cylinder containing a pinhole was placed around the subject (a small animal). The cylinder was equipped with a non-collimator gamma camera, and dual-isotope ( 99mTc-MIBI and 18F-FDG) SPECT was performed on a Wistar King Aptekman/hok (WKAH) rat. System planar sensitivity and Full-Width at Half-Maximum (FWHM) were measured for each radionuclide. System planar sensitivities for 99mTc and 18F SPECT were 2 and 7 cps/MBq, respectively. FWHMs for 99mTc and 18F SPECT were 2.0±0.5 and 2.7±0.5 mm, respectively. The collimator is relatively light (23 kg), and thus SPECT projection data could be acquired by rotating the gamma camera while the object remained stationary. The pinhole collimator can be used with a conventional rotating gamma camera. The present study demonstrated that it is possible to image organs in vivo in sufficient detail using the newly developed pinhole collimator. Further refinements to the experimental procedure may provide simultaneous high-resolution imaging of small animals using positron and gamma emitters with this collimator.

Therapy with somatostatin analogs in patient with orbitopathy and positive Octreoscan

We prospectively evaluated 28 persons with active endocrine ophthalmopathy and positive sonographic criteria (A-mode) on extraocular eye muscles. To evaluate somatostatin-receptor status SPECT of the orbits was performed with a double-headed rotating gamma camera after application of 110 MBq 111-In-Pentreotide. 9 patients (12/56 eyes respectively) showed a marked uptake ratio (> 2 in circular ROIs by semiquantitative calculation) and were selected for lanreotide (30 mg i.m. every 14 d) treatment. 5 individuals had control scan after clinical progression which became positive in two of them. All but one tolerated modest side-effects of lanreotide treatment (diarrhea). Therapy was discontinued after 3-10 months when thyroid eye disease had lead to fibrotic stage. This subgroup, with the exception of two women, who received corticosteroids additionally, presented stable disease. One of those had to be sent to surgery because of endangered optical nerve. Clinical ophthalmological control showed promising results in patients receiving somatostatin analogues at early stage when positive on octreo-scan.

Combined magnetic resonance imaging and single-photon emission tomography scanning in the discrimination of Alzheimer's disease from age-matched controls.

To compare the utility of temporal lobe magnetic resonance imaging (MRI) and single-photon emission tomography (SPET) scanning in discriminating between subjects with Alzheimer's disease (AD) and age-matched controls. Thirty subjects with NINCDS-ADRDA AD (23 probable AD, 5 possible AD, 2 definite AD) and 22 age- and sex-matched controls underwent T1-weighted coronal MRI scanning (0.3 T) and technetium 99m-HMPAO SPET scanning. MRI scans were analyzed using a digitizer system with volumes of hippocampus, amygdala, entorhinal cortex, parahippocampal gyrus, and whole cerebral cortex calculated. From SPET scans, regional cerebral blood flow (rCBF) was assessed in anterior and posterior frontal, parietal, occipital, and mesial temporal cortex using a region of interest analysis with the cerebellum as a reference area. Using MRI, the areas that best separated groups were left hippocampal and left amygdala volume, resulting in correct classification (patient vs. control) in 79% of cases (sensitivity 77%, specificity 82%). Exactly the same proportion of subjects were correctly classified by SPET, with the most discriminating rCBF changes being left parietal and right posterior frontal. Combining information from both scans improved the proportion of correctly classified subjects in a discriminant function to 90% (sensitivity 93%, specificity 86%; only 2 AD and 3 controls misclassified). All AD subjects had abnormalities on MRI and/or SPET (sensitivity for combined examinations 100%), while abnormalities on both MRI and SPET had a positive predictive value of 100% for dementia (including the detection of one control subject who later had dementia). Significant correlations between MRI and SPET measures were seen in control subjects but not in patients. Both 0.3 T MRI and single rotating gamma camera SPET were equally useful in separating AD subjects from age-matched controls, although the combination of both significantly enhanced discrimination. In particular, all AD subjects had abnormalities on either MRI or SPET and both techniques may have an important role in assisting with clinical diagnosis, though replication in other centers and examination of differentiation of AD from other causes of dementia need to be examined.

Occipital hypoperfusion on SPECT in dementia with Lewy bodies but not AD.

To compare regional cerebral blood flow (rCBF) changes using 99mTc-hexamethylpropyleneamine oxime (99mTc-HMPAO) SPECT in subjects with dementia with Lewy bodies (DLB) and AD and in normal age-matched control subjects; to examine the utility of SPECT changes in the differential diagnosis of AD and DLB. Whole-brain SPECT scans were acquired using a single-headed rotating gamma camera (IGE CamStar XR/T) in elderly subjects with consensus criteria DLB (n = 23; mean age = 79.4 years), National Institute of Neurological and Communicative Disorders and Stroke-Alzheimer's Disease and Related Disorders Association AD (n = 50; 81.9 years), and normal control subjects (n = 20; 78.1 years) after injection with 500 MBq of 99mTc-HMPAO. Region-of-interest analysis was performed using a SPECT template registered in Talairach space, with rCBF normalized to cerebellum. Both DLB and AD subjects had significantly reduced rCBF in parietal and temporal regions compared with the control subjects. The AD group also showed a significant reduction in rCBF in the frontal and medial temporal regions and the DLB in the occipital areas compared with control subjects. AD and DLB groups differed only in occipital perfusion (p < 0.01). SPECT measures (occipital and medial temporal) correctly classified 69% of all subjects, with a 65% sensitivity and 87% specificity for DLB against AD and control subjects. Temporoparietal hypoperfusion on SPECT is common to both AD and DLB. Occipital hypoperfusion is more frequently seen in DLB. Although not diagnostically specific in individual cases, occipital hypoperfusion on SPECT should raise suspicion that DLB may be the cause of dementia, prompting careful search for other features of the disorder.

Investigation of the vertebrobasilar arterial system in vertigo by vestibulocochlear test, SPECT and angiography

Objective: Perfusion of the areas of cochleovestibular structures was investigated using Tc-99m HMPAO single photon emission computerized tomography (SPECT) in the young patients with vertigo presumed to have peripheral vestibular abnormalities and compared the results with cochleovestibular test results, and vertebrobasilar angiography findings. Methods and patients: The study was performed on 20 patients with vertigo and 17 control subjects who had performed vertebral arteriography due to another disease. The patients with vertigo presumed to be on peripheral vestibular disorder were included in the study. Systemic and otorhinolaryngological examination were carried out. Audiovestibular function was evaluated in all patients and control subjects. Brain SPECT was performed with a one-head rotating gamma camera system from 64 projections into a 64×64 matrix, using low energy and high-resolution fan beam collimators with a sampling time of 30 s. The images taken from cerebellum, temporal, parietal and occipital lobes which are supplied by a vertebrobasilar system were compared visually with the other side and asymmetry in the perfusion was searched. After cochleovestibular tests and laboratory had been completed, vertebral arteriography was performed bilaterally in all patients. Results of digital subtraction angiography (DSA) and the vestibulocochlear test were compared with images of SPECT. Data analysis was done with Yates χ 2 and percentages of sensitivity and specificity were calculated. Results: There was vestibular test and cochlear test abnormalities in eight and ten of the patients with vertigo, respectively. SPECT imaging showed hypoperfusion and decreased regional blood flow in 12 of the patients. There was statistically significant differences between the study and control groups in SPECT ( P<0.05). Five patients showed abnormal findings in DSA examinations. Conclusion: It is believed that SPECT may be helpful in the detection of vascular pathology in the patients with vertigo.

Optimizing rotating gamma camera PET for brain imaging

Several acquisition geometries were investigated to optimize coincidence count rates and coincidence/singles rate ratios for brain imaging on a rotating gamma camera PET system. Detection efficiency and singles count rate limits on these systems dictate that keeping unused singles from hitting the cameras should improve coincidence rates if radiotracer doses can be adjusted to match the singles detection efficiency of the system. Radius of rotation and camera field of view were adjusted within the constraints of patient positioning. Acquisitions were done with transaxial septa on a graded absorber, and with graded absorber alone. Phantoms included a Ge-68 pin source and an extended head-thorax phantom with F-18 solution. Coincidence detection efficiency was best for the absorber only, with a small radius of rotation. Coincidence/singles ratio was best for graded absorber with small radius of rotation and axial camera field limited to 27 cm. The septa yielded a slightly lower coincidence/singles ratio, but their reduction of scatter and restriction of incidence angle of detected photons (leading to higher spatial resolution) makes their use favorable.

SPECT VISUALISATION OF FLOW THROUGH ARTIFICIAL ORGANS

A measuring set up has been designed to visualise the flow profile in a hollow fiber dialyser (Fresenhis F6) and an artificial lung (Cobe Optima) by means of SPECT techniques. A computer controlled injection system using an electronic valve was developed. Optimisation of the injected volume (radioactive solution of 99mTc) and the speed of injection was necessary to get minimal flow perturbation and a plausible image acquisition. Images are taken by 2 fixed positioned gamma cameras resulting in 2D pictures. Using water instead of blood, the flow rates needed to be adjusted to account the difference in viscosity (factor 2.5). To visualise the flow (100ml/min) in the blood compartment of the dialyser, transport through the membrane is avoided by using high molecular weight radioactive tracers (60kD). Between successive measurements, a rinsing time of 5 minutes is taken into account to remove radioactivity. Because of the hydrophobic membrane and the higher flow rate (2.61/min) in an artificial lung, high molecular weight tracers and rinsing time are unnecessary. The concentration profile in a hollow fiber dialyser shows a lower velocity in the centre. The remarkable activity accumulation in the headers could be due to the adhesion of radioactive tracers to the plastic tube. The 2D imaging of the artificial lung shows very clearly the concentration distribution over time and can be used for understanding the complex flow profile. Because of the axisymmetric shape of the blood compartment in a dialyser, the 2D images can be used to evaluate optimal flow distribution of current and future dialysers. To study in greater detail the flow through an artificial lung, a 3D image should be created using rotating gamma cameras.

Tc-99m HMPAO brain perfusion imaging in young Down's syndrome patients.

Down's syndrome (DS) is characterized by moderate mental retardation and a variety of abnormalities involving multiple organ systems. There is a high incidence of Alzheimer's disease (AD) type dementia beyond the age of 35. In this study, single photon emission computed tomography (SPECT) brain perfusion imaging of young Down's syndrome patients was performed to define the perfusion pattern. Tc-99m HMPAO brain perfusion SPECT was performed on 17 young DS patients, aged 3-24 years (mean: 10.9+/-5.9 years). None of the patients had dementia symptoms. Brain perfusion scans were acquired 15 min after i.v. injection of 12 MBq/kg of Tc-99m HMPAO using a single head rotating gamma camera. Images were analyzed visually and semiquantitatively by defining side-to-side asymmetry index. Nine DS cases showed normal brain perfusion. Eight of the 17 cases revealed mostly unilateral parieto-temporal, parieto-occipital and frontal hypoperfusions. The side-to-side asymmetry indices for these visually interpreted regional brain perfusion abnormalities ranged from 6 to 15%. These findings revealing mostly unilateral parieto-temporal and frontal hypoperfusions may not be considered as predictive patterns of dementia related Alzheimer type perfusion deficits in DS. However, such findings may connect to other functional imaging studies related to the higher cortical dysfunction in mental retardation.

めまい症例におけるＳＰＥＣＴの有用性 Ｘ線ＧＴ，ＭＲＩとの比較検討

A total of 204 patients with vertigo or dizziness were examined using N-isopropylp-(I-123) iodoamphetamine (IMP) and single photon emission computed tomography (SPECT) and the findings were compared to X-ray CT and magnetic resonance imaging (MRI) findings. SPECT was performed using a rotating gamma camera. Decreased IMP in the cerebellum and brain stem was observed in 123/204 (60.3%) studies of these patients. Of these 123 patients, 98 were diagnosed as having a vascular disorder. All 98 patients were examined by X-ray CT and only 12 patients (12/98, 12.2%) showed vascular lesions by X-ray CT. Of the 98 patients, 26 were assessed by MRI and 8 patients (8/26, 30.8%) showed vascular lesions.Our findings showed that most patients with vertigo or dizziness of so-called vertebro-basilar insufficiency (VBI) may have some vertebral blood flow disorder, which in some cases is not clearly diagnosed by conventional vestibular examinations, X-ray CT or MRI.SPECT with IMP would likely be useful to evaluate abnormal cerebellar and brain stem perfusion.

Characterization of a pinhole tomograph with 180° acquisition

Pinhole single photon emission computed tomography (SPECT) offers attractions for thyroid imaging, but acquisition must be limited to 180/spl deg/. The authors have mounted a 3.2 mm pinhole collimator on a rotating gamma camera, magnification 2.1, and characterized its response in the 10 cm field-of-view (FOV) by imaging points, lines, and a Picker thyroid phantom. The authors compared both full and half-circle data acquisition. Image reconstruction was done with a new Discrete Vertex Set (DVS) algorithm and the Feldkamp (FDK) algorithm. For full-circle acquisition, spatial resolution is quite uniform across the FOV, averaging 5.3 mm FWHM, and the reconstructed images show an intensity variation less than 5% in all directions; the FDK and DVS algorithms perform similarly. For half-circle reconstruction, spatial resolution shows more variation across the FOV, averaging 5.4 mm FWHM, and the maximum intensity variation is /spl plusmn/20%. Some differences between the FDK and DVS algorithms are apparent. The point response at non-centered positions along the horizontal transverse axis shows tails in the horizontal transverse direction for the FDK-half reconstruction, whereas for the DVS-half reconstruction there is blurring in the vertical direction at these positions. The thyroid phantom with its 6, 9, and 12 mm cold spots and 12 mm hot spot can be visualized in both full and half-circle reconstructions, allowing size determination.