Single-photon Tomography Research Articles

A YSO/LSO phoswich array detector for single and coincidence photon imaging

The performance of a phoswich array detector module for possible use in a combined single and coincidence photon imaging system has been evaluated. The detector consist of a linear array of discrete 4/spl times/4/spl times/15 mm/sup 3/ YSO elements coupled to a combined detector array/light guide of LSO, 10 mm thick. Since the scintillation light decay time is different in YSO and LSO (70 and 40 ns, respectively), events originating from the two detector materials can be separated by pulse shape discrimination. The front layer of YSO could then be used for detection of low energy, single photon events and the LSO layer for coincidence detection of annihilation radiation. The light collection of the PMTs coupled to the detector was found to be adequate to accurately identify each detector element in the array using the same positioning logic used in conventional EGO block detectors. The average energy resolution of the YSO elements at 140 keV for the block detector was found to be 14.5% FWHM, ranging from 13.8 to 15.4%. Spatial resolution of the detector block in single photon mode, using a high resolution collimator (geometric resolution 6.5 mm at 10 cm) was measured by scanning a /sup 99m/Tc line source. The resolution at 5 and 10 cm from the collimator face was found to be 5.9 and 8.5 mm FWHM, respectively.

PROGRESS IN NUCLEAR MEDICINE IMAGING OF CANCERS

Nuclear imaging is assuming an increasing role in the management of patients with cancer. A variety of new radiopharmaceuticals, several antibody or peptide based, as well as innovative uses of existing radiopharmaceuticals, mean that most nuclear medicine departments equipped with standard imaging devices can image the single photon imaging agents without difficulty.

Brain volumes and regional cerebral blood flow in carriers of the Swedish Alzheimer amyloid protein mutation.

As a preliminary part of a longitudinal clinical study of carriers of the Swedish amyloid precursor protein (APP) 670/671 mutation, 13 members of a family were investigated with magnetic resonance imaging (MRI) brain volumetry and single photon emission computed tomography (SPECT) cerebral blood flow (CBF) measurements. Five of the family members were mutation carriers; eight were not carriers. Two carriers were younger than 40 years of age and had no evidence of cognitive dysfunction or structural or functional brain changes. One carrier with 4 years to expected disease onset showed poor performance in episodic memory tests and also slightly low temporal lobe CBF, although there were no clearly abnormal findings. One carrier with mild Alzheimer disease (AD) had no clear structural brain changes, although CBF measurements showed clear reduction of temporal lobe CBF. One carrier with severe AD had both temporal lobe atrophy and CBF reduction. This indicates that in carriers of the APP 670/671 mutation, reduction of regional CBF is more severe than regional atrophy. The clearest change related to development of clinical AD was a reduction of CBF in the basal and lateral temporal lobes. Further longitudinal studies of these subjects are needed to confirm these preliminary findings, which might provide important data regarding early brain changes in AD.

Inferior Temporal Lobe Atrophy and APOE Genotypes in Alzheimer’s Disease

The apolipoprotein E (APOE) gene σ4 allele is known to be associated with late-onset familial and sporadic Alzheimer’s disease (AD). We assessed the possible relationship between APOE genotypes and morphological or functional changes in AD brains by x-ray computed tomography (CT), magnetic resonance imaging (MRI) and Xe-133 single photon emission CT (SPECT). First, we estimated the change in size of the whole brain and total ventricular system by using two x-ray CT indices, the cerebral index (CI) and ventricular index (VI), respectively. Neither CI nor VI differed significantly among APOE genotypes. Then, we focused on the inferior temporal lobe regions by introducing new MRI indices, the inferior temporal index (ITI), temporal horn index (THI) and infero-medial temporal index (IMTI). We found a significant difference in each MRI index among APOE subgroups; ITI and IMTI were lower, while THI was higher in AD patients with at least one APOE σ4 allele (σ4+ group) than in those without such an allele (σ4– group). Finally, we compared relative regional cerebral blood flow (rCBF) of Xe-133 SPECT among the AD subgroups. Relative rCBF in the cerebral cortex, particularly in the temporal lobe, was lower in the σ4+ group than in the σ4– group. These results indicate that possession, and thus expression, of the APOE σ4 allele affects preferentially the inferior temporal lobe, encompassing the hippocampus and amygdala, in AD patients.

Observation of UV photons with a microdot chamber

Microdot gas chambers have been developed which are suitable for imaging x-rays or minimum ionising particles. The problems encountered in the extension of the operating region to gains of over 10000 are described. Results obtained from single photo electron extraction by a UV source from the aluminium drift cathode are presented at avalanche gains of up to 30000. A solution is proposed, which will allow the imaging of single UV photons with less than 60 microns precision in both x and y directions simultaneously, using a detector integrated on to a quartz substrate.

Novel technetium-99m-labeled platelet GPIIb/IIIa receptor antagonists as potential imaging agents for venous and arterial thrombosis

OBJECTIVES Either venous or arterial thrombosis is a potentially life-threatening event and existing diagnostic modalities are inadequate to diagnose and to determine the morphology of the evolving thrombus. Thus development of a noninvasive imaging agent that can detect clot location remains a critical and unmet need in nuclear diagnostic medicine. The present study was undertaken to determine the potential of platelet GPIIb/IIIa receptors compared with direct thrombin inhibitors, in the detection of venous and arterial clots. METHODS Initially, the validity of exploiting the degree and extent of specific uptake and retention of a potent GPIIb/IIIa receptor antagonist in venous and in arterial thrombus was confirmed in vitro in artificially created arterial- or venous-type clots, using the radiolabeled antagonist, 3H-DMP728. This was followed by comparing the in-vivo clot/blood distribution of various technetium-99m (99mTc)-labeled, DMP728-derived, GPIIb/IIIa receptor antagonists and of thrombin inhibitors, over time, in mixed arterial/venous or venous clots in arteriovenous shunt and in venous clot models in dogs. In addition, we performed noninvasive single-photon emission tomographic imaging of the venous clot in a deep vein thrombosis model in dogs. RESULTS Our data confirmed that potency for the platelet GPIIb/IIIa receptors was maintained after radiolabeling of the parent active GPIIb/IIIa receptor antagonists. DMP728 demonstrated a relatively greater affinity for activated than for unactivated human platelets, which might be essential for attaining an optimal thrombus/blood (target/background) distribution ratio and the optimal detection of small clots (i.e. greater sensitivity). CONCLUSIONS These data suggest a potential utility of 99mTc-GPIIb/IIIa receptor antagonists, but not of direct thrombin inhibitors, in the diagnosis of venous clots in deep vein thrombosis, pulmonary embolism and arterial thromboembolic disorders including stroke and coronary and peripheral artery thrombotic disorders.

Novel technetium-99m-labeled platelet GPIIb/IIIa receptor antagonists as potential imaging agents for venous and arterial thrombosis

Either venous or arterial thrombosis is a potentially life-threatening event and existing diagnostic modalities are inadequate to diagnose and to determine the morphology of the evolving thrombus. Thus development of a noninvasive imaging agent that can detect clot location remains a critical and unmet need in nuclear diagnostic medicine. The present study was undertaken to determine the potential of platelet GPIIb/IIIa receptors compared with direct thrombin inhibitors, in the detection of venous and arterial clots. Initially, the validity of exploiting the degree and extent of specific uptake and retention of a potent GPIIb/IIIa receptor antagonist in venous and in arterial thrombus was confirmed in vitro in artificially created arterial- or venous-type clots, using the radiolabeled antagonist, 3H-DMP728. This was followed by comparing the in-vivo clot/blood distribution of various technetium-99m (99mTc)-labeled, DMP728-derived, GPIIb/IIIa receptor antagonists and of thrombin inhibitors, over time, in mixed arterial/venous or venous clots in arteriovenous shunt and in venous clot models in dogs. In addition, we performed noninvasive single-photon emission tomographic imaging of the venous clot in a deep vein thrombosis model in dogs. Our data confirmed that potency for the platelet GPIIb/IIIa receptors was maintained after radiolabeling of the parent active GPIIb/IIIa receptor antagonists. DMP728 demonstrated a relatively greater affinity for activated than for unactivated human platelets, which might be essential for attaining an optimal thrombus/blood (target/background) distribution ratio and the optimal detection of small clots (i.e. greater sensitivity). These data suggest a potential utility of 99mTc-GPIIb/IIIa receptor antagonists, but not of direct thrombin inhibitors, in the diagnosis of venous clots in deep vein thrombosis, pulmonary embolism and arterial thromboembolic disorders including stroke and coronary and peripheral artery thrombotic disorders.

Novel technetium-99m-labeled platelet GPIIb/llla receptor antagonists as potential imaging agents for venous and arterial thrombosis

Objectives Either venous or arterial thrombosis is a potentially life-threatening event and existing diagnostic modalities are inadequate to diagnose and to determine the morphology of the evolving thrombus. Thus development of a noninvasive imaging agent that can detect clot location remains a critical and unmet need in nuclear diagnostic medicine. The present study was undertaken to determine the potential of platelet GPIIb/IIIa receptors compared with direct thrombin inhibitors, in the detection of venous and arterial clots. Methods Initially, the validity of exploiting the degree and extent of specific uptake and retention of a potent GPIIb/IIIa receptor antagonist in venous and in arterial thrombus was confirmed in vitro in artificially created arterial- or venous-type clots, using the radiolabeled antagonist, 3H-DMP728. This was followed by comparing the in-vivo clot/blood distribution of various technetium-99m (99mTc)-labeled, DMP728-derived, GPIIb/IIIa receptor antagonists and of thrombin inhibitors, over time, in mixed arterial/venous or venous clots in arteriovenous shunt and in venous clot models in dogs. In addition, we performed noninvasive single-photon emission tomographic imaging of the venous clot in a deep vein thrombosis model in dogs. Results Our data confirmed that potency for the platelet GPIIb/IIIa receptors was maintained after radiolabeling of the parent active GPIIb/IIIa receptor antagonists. DMP728 demonstrated a relatively greater affinity for activated than for unactivated human platelets, which might be essential for attaining an optimal thrombus/blood (target/background) distribution ratio and the optimal detection of small clots (i.e. greater sensitivity). Conclusions These data suggest a potential utility of 99mTc-GPIIb/IIIa receptor antagonists, but not of direct thrombin inhibitors, in the diagnosis of venous clots in deep vein thrombosis, pulmonary embolism and arterial thromboembolic disorders including stroke and coronary and peripheral artery thrombotic disorders. Coronary Artery Dis 9:131-141 ©1988 Lippincott-Raven Publishers.

Advances in the diagnosis and therapy of adrenal tumors.

There continues to be controversy regarding the optimal evaluation and treatment of adrenal tumors. Magnetic resonance imaging, metaiodobenzylguanidine scan, single-photon emission tomography imaging, endoscopic ultrasound, and radiolabeled somatostatin analogues are just a few of the newer imaging techniques being investigated to improve our ability to obtain a specific diagnosis of an adrenal mass. Although the diagnosis and treatment of pheochromocytomas are relatively straightforward, the evaluation and treatment of incidentally discovered adrenal masses is less clear-cut. The management of an incidentaloma is guided by two principle considerations: whether the tumor has hormonal activity, and its malignant potential. In addition to diagnostic advances, refinements continue to be made regarding surgical management of these lesions. Laparoscopic adrenalectomy is fast becoming the procedure of choice for benign-appearing adrenal masses with appropriate indications for operative removal.

Single-photon emission tomography imaging of monoamine transporters in impulsive violent behaviour.

Several studies have shown that impulsive violent and suicidal behaviour is associated with a central serotonin deficit, but until now it has not been possible to use laboratory tests with high sensitivity and specificity to study this kind of deficit or to localize the sites of serotonergic abnormalities in the living human brain. The aim of this study was to test the hypothesis that monoamine transporter density in brain is decreased in subjects with impulsive violent behaviour. We studied serotonin (5-HT) and dopamine (DA) transporter specific binding in 52 subjects (21 impulsive violent offenders, 21 age- and sex-matched healthy controls, and ten non-violent alcoholic controls) with single-photon emission tomography (SPET) using iodine-123-labelled 2beta-carbomethoxy-3beta(4-iodophenyl)tropane ([123I]beta-CIT) as the tracer. The blind quantitative analysis revealed that the 5-HT specific binding of [123I]beta-CIT in the midbrain of violent offenders was lower than that in the healthy control subjects (P<0. 005; t test) or the non-violent alcoholics (P<0.05). The results imply that habitual impulsive aggressive behaviour in man is associated with a decrease in the 5-HT transporter density.

A brain imaging (single photon emission computerized tomography) study of semantic and affective processing in psychopaths

Psychopaths have been described as human predators who use charm, intimidation, and violence to control others and to satisfy their own needs. Underlying their propensity to violate social norms and expectations is a profound lack of empathy, guilt, or remorse, affective processes that have long resisted scientific investigation. Using brain imaging technology we found that psychopaths differed from nonpsychopaths in the pattern of relative cerebral blood flow during processing of emotional words. The results were consistent with the hypothesis that there are anomalies in the way psychopaths process semantic and affective information.

Neuroimaging in dementia

This review covers publications concerning structural brain imaging in dementia (magnetic resonance imaging) and functional brain imaging in dementia (positron emission tomography, single-photon emission tomography and functional magnetic resonance imaging). What emerges from the literature is the pivotal role that imaging, both structural and functional, currently plays in clinical studies in the field of the dementias.

A comparative study of technetium-99m sestamibi and technetium-99m tetrofosmin single-photon tomography in the detection of nasopharyngeal carcinoma

A comparative study of technetium-99m sestamibi and technetium-99m tetrofosmin single-photon tomography in the detection of nasopharyngeal carcinoma

Single photon imaging X-ray spectrometers using low noise current preamplifiers with dc voltage bias

We have developed superconducting single-photon imaging X-ray detectors with an energy resolution of 54 eV at 6 keV and a spatial resolution of 1 /spl mu/m over an effective length of 40 /spl mu/m. They utilize a current-sensitive low-noise preamplifier with a dc voltage bias. It has a signal bandwidth of 300 kHz, current noise of i/sub n/=0.26 pA//spl radic/(Hz) and voltage noise of e/sub n/=0.5 nV//spl radic/(Hz) with an input capacitance of 200 pF under operating conditions. Injected pulses with a charge Q=3.7/spl middot/10/sup 6/ electrons have been measured with a standard deviation /spl sigma/Q=3400 electrons, corresponding to an electronic noise of 13 eV at 6 keV.

Pinhole aperture design for /sup 131/I tumor imaging

A new pinhole aperture design for single photon imaging is introduced whose distinctive feature is a cylindrical channeled aperture. This allows greater attenuation near the pinhole aperture, which is especially important when imaging /sup 131/I with its medium and high energy emissions. The new design reduces to a conventional knife-edge aperture when the channel height is zero. Point source response functions were simulated for pinhole inserts with different pinhole diameters (0.4-2.0 mm diameter) and channel heights (0.1-3.0 mm) with acquisition parameters appropriate for /sup 131/I brain tumor imaging. A photon transport simulation code was used to comprehensively model photon transport and detection. Tradeoff curves between resolution and sensitivity suggest that varying pinhole diameter and channel height to achieve higher resolution at the expense of decreased sensitivity may be advantageous for imaging tumors with intratumoral administration of /sup 131/I radiolabeled monoclonal antibodies.

Performance of a YSO/LSO phoswich detector for use in a PET/SPECT system

The performance of a YSO/LSO phoswich detector module is evaluated for potential use as in a combined PET/SPECT imaging system. The high light output of LSO (/spl sim/5-6 times EGO) would allow the construction of a detector block that would have similar intrinsic resolution characteristics at 140 keV as a conventional high resolution EGO block detector at 511 keV (/spl sim/4 mm FWHM). However, the intrinsic radioactivity of LSO prevents the use of this scintillator in single photon counting mode. YSO is a scintillator with higher light output than LSO but worse absorption characteristics than LSO at higher energies. In a phoswich detector block the two detector materials are combined, where YSO is placed in a front layer and is used for single photon imaging and LSO in a second layer is used for PET imaging. Since the scintillation decay times in YSO and LSO are significantly different (70 and 40 ns, respectively), events in the two detector materials can be separated by pulse shape discrimination. In measurements of the system resolution using a high resolution collimator, the spatial resolution at 10 cm collimator distance was 8.5 mm for the phoswich detector compared to 7.6 mm for a conventional scintillation camera. However, in SPECT simulations of the two detector systems of a 20 cm diameter hot spot phantom imaged at different collimator distances using a high resolution collimator, no appreciable difference in resolution was seen in the reconstructed images between the two camera systems, including the ideal situation of zero distance between collimator and phantom.

Two-photon fluorescence microscopy with a diode-pumped Cr:LiSAF laser

We demonstrate the acquisition of high-quality two-photon fluorescence microscopy images using an all-solid-state self-mode-locked Cr:LiSAF laser. We contrast the performance of the two-photon technique with single-photon confocal fluorescence microscopy images taken with an argon-ion laser. Examples of improved depth penetration and reduced dye bleaching are presented.

Reduction in cortical IMP-SPET tracer uptake with recent cigarette consumption in a young group of healthy males. San Diego HIV Neurobehavioral Research Center.

Functional brain imaging techniques are being used increasingly to infer disturbances in brain function in various neuropsychiatric disorders, but the specificity of such findings is not always clear. We retrospectively examined the effects of one possible confound - cigarette smoking - on cortical uptake of iodine-123 iodoamphetamine (IMP) using single-photon emission tomographic imaging in a young (mean age=35 years) healthy group of male controls divided according to their smoking history. Subjects who had never smoked (n=17), or those with a history of smoking but no recent smoking (n=8), had equivalent and significantly higher mean cortical uptake of IMP than subjects with a history of smoking and who were current smokers (n=8). There were no differences in the cortical distribution of IMP. Our results indicate that cigarette smoking has an acute effect on global cerebral blood flow. This potential confound must be considered before abnormalities in cortical tracer uptake are attributed to some neuropsychiatric disorder of interest.

Detector for spatial and temporal imaging of single photons

A photon detector with spatial and temporal resolution capabilities is described. The detector consists of an image intensifier and a position-sensitive photomultiplier tube. It has 2.5×103 resolvable pixels, a dark count rate of 5×10−2 pixel−1 s−1, and a quantum efficiency of 12% at 670 nm. The maximum data rate for a pixel is 500 kHz, which is also the limit of the entire detector aperture. The absolute time of a single event can be determined to within 100 ns. The single pixel response was found to be linear with incident intensity for short pulses of light containing up to several thousand photons.

Sturge-Weber Syndrome Revisited: The Role of Neuroradiology

In this article I review the typical clinical and neuroradiological features of Sturge-Weber syndrome and introduce some of the recently described findings demonstrated by magnetic resonance imaging and perfusion-based single photon emission computed tomography. The article is concluded by a discussion into the most efficient way of imaging children with Sturge-Weber syndrome.