Gamma Camera Technology Research Articles

Technical concepts on blood pool phase SPECT (acquisition, reconstruction).

Guidelines for bone scintigraphy are well established and recommend the use of planar early phase images to investigate a number of clinical indications. With recent advances in gamma camera technology the use of SPECT/CT imaging in the early phases is now possible, offering the potential of improved diagnostic confidence and prognostic value. To date little work has been carried out to optimize the acquisition of early phase bone images using SPECT/CT with most of the available studies acquiring SPECT images after the traditional planar images to allow comparison of the two techniques. Imaging durations of 7 to 10 minutes have been commonly used. However, the use of iterative reconstruction algorithms has been investigated with rapid SPECT imaging to allow imaging durations as low as 4 minutes. The use of CZT based systems with increased sensitivity and improved energy and spatial resolution also offers the potential to reduce imaging times. The optimization of projection measurement order has been investigated as a method of reducing image artefacts as a result of changing tracer distribution during the SPECT acquisition. In this article we consider the current state of early phase SPECT imaging and possible areas for future investigation as well as recommendations for departments looking to adopt blood pool SPECT imaging as part of their routine clinical practice.

Skeletal scintigraphy with SPECT/CT in benign pediatric bone conditions

Benign bone diseases present an ongoing challenge for pediatricians. Most of them are not life threatening, but may be associated with significant morbidity. Benign space occupying lesions are a source of pain and/or pathological fractures. Their symptoms may raise concern for malignancy and require a complex diagnostic workup. Late or inadequate treatment of bone infections may result in bone and joint destruction and lifelong functional impairment especially in young children. Bone damage due to altered blood supply or due to minor trauma can be difficult to identify. MRI is a cornerstone in modern assessment of pediatric bone disease, but bone scintigraphy remains a useful tool in this clinical field. Unlike MRI, bone scans are widely available, provide whole body rather than focused exploration, are less affected by metallic implants or devices and combined with CT in hybrid SPECT/CT systems, allow visualization of bone morphology and metabolism in a single imaging session. The clinical indication and imaging technique of skeletal SPECT/CT in children are still evolving although the benefit of this technique in evaluation of children with bone pain and/or serendipitously found bone lesions seems ascertained. Improvements in gamma camera technology allow the obtaining of high quality images with either shorter acquisition times and /or reduced radiopharmaceutical administered activities. Sedation is required much less for bone scans than for MRI.

In vivo quantification of (177)Lu with planar whole-body and SPECT/CT gamma camera imaging.

BackgroundAdvances in gamma camera technology and the emergence of a number of new theranostic radiopharmaceutical pairings have re-awakened interest in in vivo quantification with single-photon-emitting radionuclides. We have implemented and validated methodology to provide quantitative imaging of 177Lu for 2D whole-body planar studies and for 3D tomographic imaging with single-photon emission computed tomography (SPECT)/CT.MethodsWhole-body planar scans were performed on subjects to whom a known amount of [177Lu]-DOTA-octreotate had been administered for therapy. The total radioactivity estimated from the images was compared with the known amount of the radionuclide therapy administered. In separate studies, venous blood samples were withdrawn from subjects after administration of [177Lu]-DOTA-octreotate while a SPECT acquisition was in progress and the concentration of the radionuclide in the venous blood sample compared with that estimated from large blood pool structures in the SPECT reconstruction. The total radioactivity contained within an internal SPECT calibration standard was also assessed.ResultsIn the whole-body planar scans (n = 28), the estimated total body radioactivity was accurate to within +4.6 ± 5.9 % (range −17.1 to +11.2 %) of the correct value. In the SPECT reconstructions (n = 12), the radioactivity concentration in the cardiac blood pool was accurate to within −4.0 ± 7.8 % (range −16.1 to +7.5 %) of the true value and the internal standard measurements (n = 89) were within 2.0 ± 8.5 % (range −16.3 to +24.2 %) of the known amount of radioactivity contained.ConclusionsIn our hands, state-of-the-art hybrid SPECT/CT gamma cameras were able to provide accurate estimates of in vivo radioactivity to better than, on average, ±10 % for use in biodistribution and radionuclide dosimetry calculations.

L’évaluation de la fonction ventriculaire gauche, avec une caméra à semi-conducteurs et un protocole à faible dose

IntroductionNew gamma camera technology with Cadmium-Zinc-Telluride (CZT) semiconductor detectors provides better myocardial perfusion imaging (MPI) resolution and, given the detector's high-sensitivity (better spatial and energy resolution), it reduces imaging time and radiopharmaceutical doses (better detection sensitivity). The purpose of this study was to evaluate the left ventricular function parameters obtained by a fast low-dose clinical protocol on a CZT camera (D-SPECT), compared to the measurement on cardiac magnetic resonance imaging. MethodsWe retrospectively included patients who underwent MPI on D-SPECT camera with a low-dose of Sestamibi-99mTc (120MBq for stress and 360MBq at rest for a patient of 75kg weight), and a cardiac magnetic resonance imaging, with a time less than two months. The left ventricular function was obtained at rest, with 8-frame reformatted, and analysis was performed using Quantitative Gated SPECT (QGS®) software. ResultsSeventy-seven patients were included and their mean ejection fraction (EF) was 45±13% at MRI. For D-SPECT recording, mean activity within heart area was 527±104kcps, for mean recording time 3.5±2.2min and mean of the total activity was 420±185MBq (effective dose: 3.7±1.6mSv). Correlation between D-SPECT and MRI was very good for EF (r=0.88), end-diastolic volume (EDV, r=0.90) and end-systolic volume (ESV, r=0.96), but with an underestimation of all these parameters by the D-SPECT (on average, 5% absolute value for EF, and −16% and −24% in relative values for respectively ESV and EDV). ConclusionThe evaluation of left ventricular function using the D-SPECT camera and with a fast low-dose protocol correlates well with that obtained by cardiac MRI, in the same patient. EF and ventricular volumes are however underestimated, in agreement with that previously documented with conventional Anger cameras.

Molecular breast imaging: an emerging modality for breast cancer screening.

Screening mammography is recognized as an imperfect imaging tool that performs poorly in women with dense breast tissue - a limitation which has driven demand for supplemental screening techniques. One potential supplemental technique is molecular breast imaging (MBI). Significant improvements in gamma camera technology allow MBI to be performed at low radiation doses, comparable with those of tomosynthesis and mammography. A recent screening trial in women with dense breast tissue yielded a cancer detection rate of 3.2 per 1000 for mammography alone and 12.0 per 1000 for the combination of mammography and MBI. MBI also demonstrated a lower recall rate than that of mammography. MBI is a promising supplemental screening technique in women with dense breast tissue.

ACR testing of a dedicated head SPECT unit.

Physics testing necessary for program accreditation is rigorously defined by the ACR. This testing is easily applied to most conventional SPECT systems based on gamma camera technology. The inSPira HD is a dedicated head SPECT system based on a rotating dual clamshell design that acquires data in a dual‐spiral geometry. The unique geometry and configuration force alterations of the standard ACR physics testing protocol. Various tests, such as intrinsic planar uniformity and/or resolution, do not apply. The Data Spectrum Deluxe Phantom used for conventional SPECT testing cannot fit in the inSPira HD scanner bore, making (currently) unapproved use of the Small Deluxe SPECT Phantom necessary. Matrix size, collimator type, scanning time, reconstruction method, and attenuation correction were all varied from the typically prescribed ACR instructions. Visible spheres, sphere contrast, visible rod groups, uniformity, and root mean square (RMS) noise were measured. The acquired SPECT images surpassed the minimum ACR requirements for both spatial resolution (9.5 mm spheres resolved) and contrast (6.4 mm rod groups resolved). Sphere contrast was generally high. Integral uniformity was 4% and RMS noise was 1.7%. Noise appeared more correlated than in images from a conventional SPECT scanner. Attenuation‐corrected images produced from direct CT scanning of the phantom and a manufacturer supplied model of the phantom demonstrated negligible differences.PACS numbers: 87.57.C‐, 87.57.uh, 87.63.lj

Review: comparison of PET rubidium‐82 with conventional SPECT myocardial perfusion imaging

Nuclear cardiology has for many years been focused on gamma camera technology. With ever improving cameras and software applications, this modality has developed into an important assessment tool for ischaemic heart disease. However, the development of new perfusion tracers has been scarce. While cardiac positron emission tomography (PET) so far largely has been limited to centres with on-site cyclotron, recent developments with generator produced perfusion tracers such as rubidium-82, as well as an increasing number of PET scanners installed, may enable a larger patient flow that may supersede that of gamma camera myocardial perfusion imaging.

SPECT Imaging for Detecting Coronary Artery Disease and Determining Prognosis by Noninvasive Assessment of Myocardial Perfusion and Myocardial Viability

Basic knowledge of active and passive transport mechanisms for concentrating monovalent cations in myocardial cells led to the investigation of the application of radioisotopes of potassium, thallium, rubidium, and ammonia to the in vivo noninvasive assessment of regional myocardial perfusion and viability utilizing gamma camera or positron emission tomographic (PET) imaging technology. Subsequently, technetium-99m (Tc-99m)-labeled isonitriles (sestamibi and tetrofosmin), which bind to mitochondrial membranes, emerged as superior imaging agents with single photon emission tomography (SPECT) imaging. When any of these imaging agents are injected intravenously during either exercise or pharmacologic stress, myocardial defects in tracer uptake represent either abnormal regional flow reserve or myocardial scar reflecting of coronary artery disease (CAD). The major clinical indications for stress SPECT or PET myocardial perfusion imaging are for detection of CAD as the cause of chest pain and risk stratification for prognostication. Patients with normal stress myocardial perfusion scans have an excellent prognosis with <1.0% annual rate future annual death or nonfatal infarction. The greater the extent and severity of ischemic perfusion defects (defects seen on stress images but improve on resting images), the greater the subsequent death or infarction rate during follow-up. Rest imaging alone is performed for determination of myocardial viability in patients with CAD and severe left ventricular dysfunction. Myocardial segments showing >50% uptake compared to normal uptake have a better long-term outcome with revascularization than with medical therapy with enhanced left ventricular function and improved survival. Other applications of SPECT imaging include the evaluation of cardiac sympathetic function, assessment of myocardial metabolism in health and disease, and molecular imaging of coronary atherosclerosis and myocardial stem cell therapy.

New Toys for Nuclear Cardiologists

Gordon Liljestrand is credited with establishing modern nuclear cardiology as a noninvasive imaging modality in 1939.1 Table summarizes major technological advancements in myocardial perfusion imaging over the past 70 years that have led to more accurate assessment of coronary artery disease (CAD). Most of these technical advances have involved radioisotopes and computer software. Camera hardware has undergone relatively little change since the introduction of the gamma camera, also commonly referred to as the scintillation camera, by Hal Anger in 1958.2 The gamma camera has performed admirably as the workhorse for myocardial perfusion imaging over the years but has several limitations. Sensitivity and resolution are modest. Imaging is inefficient as the heart occupies only a small portion of the field of view. Imaging places several demands on the patient, requiring relatively long imaging times (8 to 12 minutes) while lying motionless on a narrow, hard table with one or both arms fully abducted to minimize the distance between the patient's chest and the rotating detectors. The relatively long imaging times require administration of fairly high doses of radioisotopes with attendant higher radiation exposure, an issue of increasing medical and societal concern.3 View this table: Table. Developments in Nuclear Cardiology Article see p 51 In the past few years, there have been tremendous advances in gamma camera technology due to the replacement of the conventional sodium iodide (NaI)-based systems with solid-state detectors using cesium iodide coupled to photodiodes or novel semiconductor-based detectors using cadmium zinc telluride (CZT). The most promising of these new technologies is the CZT detector, which directly converts gamma radiation to an electronic pulse and thereby eliminates the need for a scintillating crystal and photomultiplier tubes. The CZT detector is substantially smaller than a NaI-based detector. In addition, the CZT detector offers substantially better energy resolution and spatial resolution than …

Stress Thallium-201/Rest Technetium-99m Sequential Dual Isotope High-Speed Myocardial Perfusion Imaging

Our purpose was to describe a novel, rapid stress thallium-201 (Tl-201)/rest technetium-99m (Tc-99m) agent myocardial perfusion imaging (MPI) protocol (Tl/Tc) with a high-speed MPI scanner and to compare this protocol with a standard rest/stress Tc-99m agent protocol (Tc/Tc) with respect to image quality and radiation dosimetry. Recent advances in gamma camera technology have provided opportunity for improved SPECT MPI protocols. A rapid Tl/Tc protocol that could improve image information while maintaining a low radiation burden for the patient would be desirable. We compared high-speed SPECT MPI studies in 374 consecutive patients undergoing exercise or pharmacologic Tl/Tc protocol to those of 262 patients undergoing rest/stress Tc/Tc protocol. Tl/Tc imaging was accomplished in <20 min. Overall image quality was good to excellent in 96% and 98% of patients with the Tl/Tc and the Tc/Tc protocols, respectively (p = ns). Beginning rest imaging within 2 min after rest injection with the Tl/Tc protocol did not result in reduced confidence in image interpretation. Early rest Tc images of the Tl/Tc protocol showed less extracardiac activity than was observed on standard rest imaging used in the Tc/Tc protocol (84% vs. 61%), respectively (p < 0.01). The normalcy rate was high in both groups (100% vs. 92%). Radiation burden was similar between the Tl/Tc and Tc/Tc protocols. A rapid stress Tl-201/rest Tc-99m protocol for use with high-speed SPECT MPI has image quality and radiation dosimetry similar to those observed with a conventional rest/stress Tc-99m protocol. The Tl/Tc protocol offers promise as an efficient and relatively low radiation dose method, in which the superior qualities of Tl-201 for stress imaging and of the Tc-99m agents for rest imaging can be preserved. The findings also suggest that with rapid imaging rest MPI immediately after Tc-99m agent injection may be superior to standard delayed image initiation.

Abstract 5818: Stress Thallium-201/Rest Tc-99m Sequential Dual Isotope High-Speed Myocardial Perfusion Imaging

Recent advances in gamma camera technology are providing opportunities for novel high-speed myocardial perfusion imaging (HS-MPI) protocols. We aimed to develop and evaluate a stress thallium-201 (Tl-201) and rest Tc-99m sestamibi or tetrofosmin imaging protocol that could reduce imaging time and radiation burden. Methods: We studied 410 consecutive patients undergoing exercise or pharmacologic low-dose stress Tl-201 HS-MPI (4 min/acquisition) in the semi-upright and supine positions (D-SPECT, Spectrum-Dynamics) followed by rest Tc-99m sestamibi (n= 139) or tetrofosmin (n= 271) with immediate post-injection rest imaging. Of 330 patients with no known coronary artery disease (CAD), 29 patients also underwent invasive coronary angiography (ICA) or coronary computed tomography angiography (CCTA) within a three month period and 36 had a &lt; 5% pre-test likelihood of CAD (LLk). Despite low injected doses [Tl-201 (2.2± 0.3 mCi) and Tc-99m sestamibi or tetrofosmin (8.9± 2.4 mCi), the 3 acquisition MPI protocol (2 stress/1 rest) was accomplished &lt; 20 minutes. The quality of stress and resting image was good to excellent in &gt;96% of cases; importantly, no or minor extracardiac activity was seen on 99% of stress and 93% of rest images. HS-MPI was nondiagnostic or uninterpretable in only 2/410 patients. In the 29 patients with CCTA or ICA, the sensitivity and specificity for the detection of ≥70% stenosis were 73% and 89%, respectively, and in 15 patients with ICA, the sensitivity was 89%. The normalcy rate in the LLk group was 100%. A fast stress Tl-201/rest Tc-99m HS-MPI protocol offers promise as a time-efficient, low radiation dose method, in which the superior qualities of Tl-201 for stress imaging and of Tc-99m agents for rest imaging can be utilized.

Radiolabeled lipid nanoparticles for diagnostic imaging

Nanoparticles are increasingly being incorporated into the design of diagnostic imaging agents. Significant research efforts have been conducted with one class of lipid nanoparticle (liposomes) radiolabeled with gamma-emitting radionuclides as radiopharmaceuticals for scintigraphic imaging of cancer, inflammation/infection and sentinel lymph node detection. This article reviews the current literature with special emphasis on the clinical studies performed with liposome radiopharmaceuticals for detection of tumors, infectious/inflammatory sites or metastatic lymph nodes. Future uses of liposome radiopharmaceuticals are also described. Characteristics required of the radionuclide, liposome formulation and radiolabeling method for an effective radiopharmaceutical are discussed. A description of the procedures and instrumentation for conducting an imaging study with liposome radiopharmaceutical is included. Clinical studies using liposome radiopharmaceuticals are summarized. Future imaging applications of first- and second-generation radiolabeled liposomes for chemodosimetry and the specific targeting of a disease process are also described. The choice of radionuclide, liposome formulation and radiolabeling method must be carefully considered during the design of a liposome radiopharmaceutical for a given application. After-loading and surface chelation methods are the most efficient and practical. Clinical studies with liposome radiopharmaceuticals demonstrated that a wide variety of tumors could be detected with good sensitivity and specificity. Liposome radiopharmaceuticals could also clearly detect various soft tissue and bone inflammatory/infectious lesions, and performed equal to or better than infection imaging agents that are approved at present. Yet, despite these favorable results, no liposome radiopharmaceutical has been approved for any indication. Some of the reasons for this can be attributed to reports of an unexpected infusion-related adverse reaction in two studies, the requirement of more complex liposome manufacturing procedures, and the adoption of other competing imaging procedures. Continued research of liposome radiopharmaceutical design based on a better understanding of liposome biology, improved radiolabeling methodologies and advances in gamma camera technology is warranted.

Reliability of symptoms to determine use of bone scans to identify bone metastases in lung cancer: prospective study

Based on the hypotheses that most skeletal metastases in lung cancer are clinically symptomatic, that the incidence of bony metastases in early stages is low, and that bone scintigraphy has...

Performance evaluation of a hand-held, semiconductor (CdZnTe)-based gamma camera.

We have designed and developed a small field of view gamma camera, the eZ SCOPE, based on use of a CdZnTe semiconductor. This device utilises proprietary signal processing technology and an interface to a computer-based imaging system. The purpose of this study was to evaluate the performance of the eZ scope in comparison with currently employed gamma camera technology. The detector is a single wafer of 5-mm-thick CdZnTe that is divided into a 16x16 array (256 pixels). The sensitive area of the detector is a square of dimension 3.2 cm. Two parallel-hole collimators are provided with the system and have a matching (256 hole) pattern to the CdZnTe detector array: a low-energy, high-resolution parallel-hole (LEHR) collimator fabricated of lead and a low-energy, high-sensitivity parallel-hole (LEHS) collimator fabricated of tungsten. Performance measurements and the data analysis were done according to the procedures of the NEMA standard. We also studied the long-term stability of the system with continuous use and variations in ambient temperature. Results were as follows. INTRINSIC ENERGY RESOLUTION: 8.6% FWHM at 141 keV.LINEARITY: There was excellent linearity between the observed photopeaks and the known gamma ray energies for the given isotopes. INTRINSIC SYSTEM UNIFORMITY: For the central field of view, the integral uniformity and the differential uniformity were, respectively, 1.6% and 1.3% with the LEHR collimator and 1.9% and 1.2% with the LEHS collimator. SYSTEM SPATIAL RESOLUTION: The FWHM measurements made at the surface of the collimator were 2.2 mm (LEHR) and 2.9 mm (LEHS).CONTRAST TEST: The average S/N ratios (i.e. counts in the irradiated pixel divided by counts in the surrounding pixels) for the inner ring pixels (8)/outer ring pixels (16) using the LEHS collimator and LEHR collimator were 3.2%/0.2% and 3.7%/0.3%, respectively. COUNT RATE CHARACTERISTICS: We could not determine the maximum count rate and the 20% loss count rate from these data because the plateau was not reached while using the solutions measured. SYSTEM SENSITIVITY: The average acquisitions were 11,052 cpm/MBq (LEHR) and 28,590 cpm/MBq (LEHS). TEMPERATURE DEPENDENCE: The system displayed minimum corresponding shift in cps with temperature changes in the measured temperature range. We designed and developed a semiconductor-based gamma camera using CdZnTe. The basic performance of this camera compares favourably with the existing gamma camera technology that is deployed in the medical field today. The most significant differences include the spatial resolution, sensitivity, high count rate characteristics and energy resolution. We believe that this device will be of value for a number of clinical applications including sentinel node detection and radiopharmaceutical-guided surgery.

Characterization of CdTe and CdZnTe detectors for gamma-ray imaging applications

CEA-LETI in association with Bicron and Crismatec has been developing solid-state gamma camera technology based on CZT. The project included gamma camera head systems development including front-end electronics with an integrated circuit (ASIC), material growth, and detector fabrication and characterization. One feature of the work is the use of linear correlation between the amplitude and the fast rise time of the signal – which corresponds to the electron transit time in the detector, a development that was reported previously and which allows more than 80% of the 122 keV γ-photons incident on HPBM material to be recovered in a ±6.5% 2D window. In the current work, we summarize other methods to improve CZT detector performance and compare them with the Bi-Parametric Spectrum (BPS) method. The BPS method can also be applied as a diagnositic. BPS curve shapes are shown to vary with electric field, and with electron transport properties, and the correction algorithims are seen to be robust over a range of values. In addition, the technique is found to improve detectors from a variety of sources including some with special electrode geometries. In all cases, the BPS method improves efficiency (>75%) without degrading energy resolution (± 6.5% 2D window) even for a monolithic detector. The method does not overcome bulk inhomogeneity nor noise which comes from low resistivity.

Complete Pathological Response to Chemotherapy for Non-Small Cell Lung Cancer Demonstrated by Gamma Camera Positron Emission Tomography

We report the case history of a 61-year- old female smoker who presented with an inoperable T2N2M0 squamous cell carcinoma of the right upper lobe bronchus. This was staged by computed tomography (CT), positron emission tomography (PET) using a modified dual-headed gamma camera, and mediastinoscopy. She then underwent three cycles of cisplatin-containing chemotherapy.After the chemotherapy, CT demonstrated a residual 10mm mass in the right upper lobe and a considerable reduction in size of the mediastinal lymphadenopathy. Functional tumour imaging with PET showed no abnormality, suggesting that there was no remaining viable tumour. At right upper lobectomy a complete pathological response was confirmed.We discuss PET, the potential new applications of gamma camera technology, and the use of cisplatin-containing chemotherapy in non-small cell lung cancer.

Positron emission tomography: establishing priorities for health technology assessment.

Positron emission tomography (PET) is an expensive diagnostic imaging technology. Despite the long history of PET development, the costs and effectiveness of its use in routine clinical practice remain unknown. Against this background of uncertainty regarding the clinical role of PET, the UK Standing Group on Health Technology requested a review of its current and potential role which would enable research priorities in this area to be established. This 3-month project had two explicit objectives: (1) to review the state of knowledge regarding the clinical applications of PET; (2) to determine the key health technology assessment (HTA) research questions relating to the use of PET in the UK. A literature review to ascertain the state of knowledge regarding the clinical applications of PET and a three-round Delphi study to inform the key HTA research questions relating to the use of PET in the UK were undertaken. The results of an earlier systematic review, published by the Veteran's Health Administration (VHA) in the USA in 1996, were used as the starting point for the literature review. The VHA review was updated and extended by means of MEDLINE and Cochrane Library database searches. Participants in the Delphi study were selected by discussion with five individuals in the UK with an interest in, and awareness of, developments in PET. As a result of their suggestions, 43 individuals were initially invited to participate, of whom two did not feel appropriately qualified. Questionnaires were sent by facsimile to all invited participants, who were asked to return the completed forms by facsimile within a week. The content and structure of the Delphi study was informed by the results of the literature review. The responses and comments of the participants were a major source of information for this report. Clinical applications for PET have been advocated in three broad disease groups: oncology, cardiology and neuropsychiatric disorders. There are currently four PET modalities that need to be considered when assessing its potential clinical role in the UK: full ring PET scanners operating in two or three dimensions (available at five sites); partial ring rotating PET scanners (one currently operating in the UK); coincidence imaging with modified gamma camera technology; and high-energy collimator imaging of 511 keV photons with modified gamma camera technology. There is a paucity of available evidence relating to the cost-effectiveness of the various PET modalities in all of the clinical indications for which the technology is currently being advocated. In addition, many existing reports on the diagnostic accuracy of PET are limited because they are liable to bias and often relate only to very small patient numbers. The results of the Delphi study indicated that the four most important research priorities for the NHS, in descending order of their importance, are: (1) the relative cost-effectiveness of (a) full ring PET, (b) gamma camera PET using coincidence imaging and (c) existing diagnostic strategies to determine staging prior to operative intervention for lung cancer; (2) partial ring PET compared with full ring PET in oncology (3) the relative cost-effectiveness of (a) full ring PET, (b) gamma camera PET using coincidence imaging and (c) existing diagnostic strategies to stage and monitor treatment response in breast cancer; (4) the relative cost-effectiveness of (a) gamma camera PET using coincidence imaging and (b) 511 keV collimated positron imaging for assessing myocardial viability when selecting patients for revascularisation surgery. Vignettes describing each of the research priorities are provided in the main report. The findings of this project, which was undertaken rapidly in order to inform HTA research prioritization in the UK, provide a contemporary overview of the potential clinical role for PET in the NHS. Evidence is needed that using PET as a diagnostic

Yttrium-90 biodistribution by yttrium-87 imaging: a theoretical feasibility analysis.

Yttrium-90 is widely used in radioimmunotherapy but does not emit photons for imaging. Indium-111, a chemically similar atom has been used instead as a tracer for the distribution of 90Y-labeled antibodies. Recent advances in gamma camera technology have made it possible to image at energies higher than 364 keV. This work provides a theoretical analysis of the feasibility of using 87Y (485 keV, 92.2% yield) as a tracer for in vivo imaging of 90Y-labeled antibodies. Yttrium-87 may be produced by the 87Sr(p,n)87Y reaction in a cyclotron and has a 3.3 day half-life. This reaction also yields a metastable state of 87Y (87mY). Yttrium-87, itself decays to a metastable state of 87Sr (87mSr). The level of these contaminants and their anticipated impact on the utility of 87Y as a tracer for 90Y are examined theoretically. Dosimetry is performed to assess the absorbed dose associated with using 87Y. A 100 h delay following the end of bombardment of an isotopically enriched 87Sr target reduces the activity of the metastable state of 87Y in the product by 10- to 15-fold, with greater delays resulting in a further reduction. A rapid equilibration between 87Y and its daughter, 87mSr, is expected, in vivo. Although strontium is known to concentrate in bone, the electron emissions of 87mSr are short range, thereby making possible biologic effects highly position dependent; the photon emissions allow for independent imaging which may be used to perform dosimetry and thereby directly assess potential toxicity. 87Y merits further consideration as an imaging tracer for 90Y.

Update in nuclear cardiology.

Imaging techniques for the noninvasive detection and evaluation of coronary artery disease continue to develop. New techniques for the quantification of myocardial blood flow by positron-emission tomography, new approaches to metabolic imaging, and new gamma camera technology have the potential to expand the scope of cardiac nuclear medicine in many facilities. Determination of the best and most cost-effective method of assessing myocardial viability in patients with advanced coronary artery disease remains of key interest with research directed at alternative 201Tl imaging protocols, fatty acid metabolism, and viability assessment with the new 99mTc-based myocardial perfusion radiopharmaceuticals. The assessment of endothelial function and determination of coronary flow reserve with 13N-ammonia positron-emission tomography may aid in the identification of preclinical atherosclerosis, and in monitoring disease progression and response to therapy. New information in radionuclide perfusion imaging in young and elderly patients and in those with interventricular conduction disturbances may allow for more accurate identification of coronary artery disease. The role of radionuclide imaging in patients with dilated cardiomyopathy continues to evolve with the development of radiolabeled chemicals of the adrenergic nervous system and their analogues, which will be helpful in the stratification of disease severity. These new imaging techniques promise to increase the accuracy of nuclear cardiology for detection of disease, assessment of function, and prognosis.