Elizabeth Prvulovich

Myocardial perfusion scintigraphy: the evidence.

This review summarises the evidence for the role of myocardial perfusion scintigraphy (MPS) in patients with known or suspected coronary artery disease. It is the product of a consensus conference organised by the British Cardiac Society, the British Nuclear Cardiology Society and the British Nuclear Medicine Society and is endorsed by the Royal College of Physicians of London and the Royal College of Radiologists. It was used to inform the UK National Institute of Clinical Excellence in their appraisal of MPS in patients with chest pain and myocardial infarction. MPS is a well-established, non-invasive imaging technique with a large body of evidence to support its effectiveness in the diagnosis and management of angina and myocardial infarction. It is more accurate than the exercise ECG in detecting myocardial ischaemia and it is the single most powerful technique for predicting future coronary events. The high diagnostic accuracy of MPS allows reliable risk stratification and guides the selection of patients for further interventions, such as revascularisation. This in turn allows more appropriate utilisation of resources, with the potential for both improved clinical outcomes and greater cost-effectiveness. Evidence from modelling and observational studies supports the enhanced cost-effectiveness associated with MPS use. In patients presenting with stable or acute chest pain, strategies of investigation involving MPS are more cost-effective than those not using the technique. MPS also has particular advantages over alternative techniques in the management of a number of patient subgroups, including women, the elderly and those with diabetes, and its use will have a favourable impact on cost-effectiveness in these groups. MPS is already an integral part of many clinical guidelines for the investigation and management of angina and myocardial infarction. However, the technique is underutilised in the UK, as judged by the inappropriately long waiting times and by comparison with the numbers of revascularisations and coronary angiograms performed. Furthermore, MPS activity levels in this country fall far short of those in comparable European countries, with about half as many scans being undertaken per year. Currently, the number of MPS studies performed annually in the UK is 1,200/million population/year. We estimate the real need to be 4,000/million/year. The current average waiting time is 20 weeks and we recommend that clinically appropriate upper limits of waiting time are 6 weeks for routine studies and 1 week for urgent studies.

A comparison of three radionuclide myocardial perfusion tracers in clinical practice: the ROBUST study.

Abstract. There are no large studies available to guide the selection of thallium (Tl), methoxyisobutylisonitrile (MIBI) or tetrofosmin (Tf) for myocardial perfusion imaging. Our objective was to compare the technical and clinical performance of the three in routine clinical practice. We randomised 2,560 patients to receive Tl, MIBI or Tf. A 1-day stress/rest protocol was used for MIBI and Tf. Tracer uptake was scored using a 17-segment model, quality and artefact scores were assigned, and ratios of heart (H), liver (L), subdiaphragmatic (S) and lung activity were measured. Mean quality scores (stress/rest) were Tl 2.13/2.16, MIBI 2.18/2.39, Tf 2.18/2.42 (P=ns stress and <0.00001 rest). For attenuation artefact, Tl>MIBI=Tf (P<0.05) and for low-count artefact Tl>MIBI>Tf (P<0.001). For H/S, Tl>MIBI=Tf, for H/L Tl>MIBI=Tf, and for H/lung Tl<MIBI=Tf. Stress defects in the patients with reversible or mixed perfusion defects were more severe for Tl than for the other tracers (mean summed score out of 68: Tl 52.3, MIBI 55.7, Tf 54.4, P<0.01), but mean rest scores were more similar (Tl 58.7, MIBI 60.7, Tf 59.4, P=0.02). In the subset of 137 patients undergoing diagnostic perfusion studies without prior infarction, angiography or revascularisation, overall sensitivity for the detection of coronary disease defined by subsequent angiography was 91% with a specificity of 87%. There were no significant differences between the tracers with regard to sensitivity and specificity. In conclusion: There are technical differences between the tracers. Overall image quality score is superior using technetium, with less low-count artefact and less attenuation. Stress defect depth and extent are slightly greater using thallium, with no difference between MIBI and tetrofosmin. All three tracers perform well in clinical terms, with high sensitivity and specificity for angiographic stenosis and no differences in accuracy between the tracers.

Effect of attenuation correction on myocardial thallium-201 distribution in patients with a low likelihood of coronary artery disease

Regional variation of tracer distribution is seen in uncorrected thallium-201 images of normal hearts. This study evaluates the effect of attenuation correction on myocardial201Tl distribution in patients with low risk of coronary artery disease. An L-shaped dualdetector single-photon emission tomographic system equipped with a pair gadolinium-153 scanning line sources was used for sequential emission/transmission imaging in 36 patients (14 men and 22 women) with less than 5% risk for coronary artery disease. Uncorrected emission images were reconstructed using filtered back-projection (FBP) whereas the attenuation corrected (AC) images were iteratively reconstructed using the attenuation map computed from the transmission data. Both sets of images were reorientated into short axis, vertical long axis and horizontal long axis images. For quantification data were reconstructed into polar plots and count density estimated in 17 myocardial segments. The population % standard deviation for each segment of AC data was significantly smaller than that for FBP data, indicating improved homogeneity of tracer distribution. In men the anterior-basal inferior activity ratio improved from 1.20 for FBP to 0.96 for AC (stress) and from 1.23 for FBP to 0.98 for AC (delay) (P<0.0001). In women the anterior-basal inferior activity ratio changed from 1.08 for FBP to 0.94 for AC (stress) and from 1.08 for FBP to 0.93 for AC (delay) (P<0.001). These ratios reflect appropriate compensation for basal attenuation but a lack of scatter correction. The lateral—septal activity ratio in men changed from 1.05 for FBP to 0.99 for AC (stress) and from 1.02 for FBP to 0.96 for AC (delay), while in women it changed from 1.05 for FBP to 0.98 for AC (stress) and from 1.04 for FBP to 0.98 for AC (delay) (P<0.005 in all cases). The apex of AC images showed a decrease in activity consistent with wall thining at this site. It is concluded that the use of attenuation correction yields improved homogeneity of myocardial tracer distribution in patients with low risk of coronary artery disease. The diagnostic benefits of attenuation correction are yet to be fully assessed.

Immunoscintigraphy with a 99Tcm-labelled anti-granulocyte monoclonal antibody in patients with human immunodeficiency virus infection and AIDS

SummaryThe value of immunoscintigraphy with technetium-99m (99Tcm) labelled anti-granulocyte monoclonal antibody (BW250/183) was studied prospectively in human immunodeficiency virus (HIV-1) antibody-positive patients presenting with fever without localizing symptoms or signs. Twenty-three studies were performed in 23 patients and the results of 99Tcm-anti-granulocyte imaging were compared with the definitive microbiological or cytological diagnosis. Twenty-one patients had an infective cause of pyrexia, one patient had disseminated lymphoma and one Kaposi sarcoma. 99Tcm-anti-granulocyte antibody imaging correctly identified the sites of infection in only five (24%) patients, four of whom had infective colitis (one also had bacterial pneumonia) and one of whom had cellulitis. Sixteen foci of infection were not localized by 99Tcm-anti-granulocyte immunoscintigraphy (false-negative scans). Six of these patients had Pneumocystis carinii pneumonia; other diagnoses in this group included bacterial or fungal pneumonia and bacteraemia secondary to line infections. 99Tcm-anti-granulocyte antibody did not accumulate in the patients with disseminated lymphoma and Kaposi sarcoma (true-negative scans). 99Tcm-anti-granulocyte imaging, therefore, appears useful in identifying extrathoracic infection in HIV-1 positive patients. Its back of sensitivity for the identification of pulmonary infection means that its role in the investigation of HIV-1 antibody-positive patients with fever without localizing symptoms or signs is limited.

Nuclear cardiology in the UK: activity and practice 1997

Abstract. A questionnaire was sent to 251 nuclear medicine centres asking for details of nuclear medicine activity, and nuclear cardiology activity and practice in 1997. One hundred and seventy-one (68%) centres replied. Nuclear medicine activity was estimated at 11.8 studies/1,000 population/year, and 9.5% of these studies were within cardiology (1.12 studies/1,000/year). Myocardial perfusion imaging (MPI) studies accounted for 77% and radionuclide ventriculography (RNV) for 22% of all nuclear cardiology. On a national basis this represents activity levels of 0.86 and 0.25 studies/1,000/year for MPI and RNV, respectively. Of the 171 responding centres, 102 (60%) performed MPI studies and 81 (79%) of these reported that activity was increasing. However, MPI activity was unevenly distributed between hospitals. Two centres accounted for 13% of total MPI; others had far lower activity rates, and 51/102 (50%) centres performed less than 200 MPI studies/year. Comparison with previous surveys showed that nuclear medicine activity had almost doubled since 1990 (it was 6.0 studies/1,000 population in 1990, 9.3 studies/1,000 in 1994 and 11.8 studies/1,000 in 1997). Over the same period, nuclear cardiology activity had also risen, the greatest increase being seen for the last 3 years (it was 0.7 studies/1,000 population in 1990, 0.82 studies/1,000 in 1994 and 1.12 studies/1,000 in 1997). Despite these encouraging figures, MPI activity for 1997 remained well below that recommended by the British Cardiac Society in 1994 (2.6 studies/1,000/year) as adequate to serve the needs of patients with cardiac disease in the UK; it was also below the European average activity for the same year (2.2 studies/1,000/year). The anticipated increased workload for nuclear cardiology is encouraging despite the wide and varied practice of nuclear cardiology around the UK. The nuclear medicine community now needs to address the issues that will prevent it keeping up with demand, such as restricted camera time, excessive waiting lists and outdated equipment, but also to standardise acquisition and reporting techniques so that all studies, wherever performed, will be of a uniformly high standard.

Nuclear cardiology in the UK: British Nuclear Cardiology Society survey 1994.

This study surveyed practice in nuclear cardiology in the UK in 1994. A questionnaire was sent to 219 centres performing nuclear imaging asking for details of current practice in nuclear cardiology. Replies were received from 192 centres (88%). Activity in performance of myocardial perfusion imaging (MPI) and radionuclide ventriculography (RNV), anticipated changes in activity, differences between regional and district general hospitals, technical imaging parameters and referral sources were surveyed. Of the responding centres, 125 (65%) performed nuclear cardiology. More regional centres (85 vs 55%, P < 0.0003) performed a higher proportion (62 vs 24%, P < 0.001) of nuclear cardiology activity compared with district general hospitals. Nuclear medicine activity was estimated at 9.3 scans/1000/year, of which 8.9% was cardiology (0.82/1000/year; MPI, 0.56/1000/year; RNV, 0.26/1000/year). A comparison with previous surveys showed a significant increase of 24% in nuclear cardiology since 1988, with a strong rise in MPI (350%); however, RNV has fallen by 47%. Myocardial perfusion activity in the UK remains very low (25 and 5% for MPI and RNV respectively) when compared with the average of 2.2/1000/year for Europe and 10.8/1000/year for the USA. In conclusion, MPI has increased on average by 23% per annum (compound rate) since 1988, but in 1994 was still only 32% of the British Cardiac Society target of 2.6 scans/1000/year. Proper resourcing for capital expenditure on new equipment and new staff will be important to maintain momentum in closing the gap. Also important is clinical understanding, as already implemented by including nuclear cardiology in guidelines for specialist cardiology training.

Transmission scanning for attenuation correction of myocardial 201Tl images in obese patients

For attenuation correction (AC) of 201Tl myocardial perfusion images, an accurate attenuation map is required. This study assessed whether prolonged transmission scanning is required in obese compared to normal-sized patients. Twenty-nine obese patients (mean body mass index 33 kg m-2) underwent sequential emission/transmission imaging for AC using an L-shaped, dual-headed gamma camera fitted with two 153Gd scanning line sources. Transmission data were acquired for 5 s per view (scan time for normal-sized patients) and for 10 s per view and used to reconstruct individual attenuation maps. Emission data were reconstructed using each attenuation map in turn to produce attenuation-corrected images (AC5 and AC10). Tracer distribution in the AC5 and AC10 images was compared by two observers blinded to study type. For each data set, count density was measured in 17 segments of a polar plot and segmental uptake expressed relative to study maximum. Although myocardial count density was low on the 5 s per view transmission images (0.5-13.0 and 3.0-14.0 counts per pixel in the anteroposterior and lateral projections respectively), no significant differences in tracer distribution were seen between the AC5 and AC10 images and these were reported identically. In addition, the mean segmental relative uptake values were similar (P > 0.05) for corresponding segments of the AC5 and AC10 images. We conclude that prolonged transmission scanning is not required in obese compared to normal-sized patients. The transmission scanning protocol used in normal-sized patients is applicable across a wide patient weight range.

Myocardial perfusion scintigraphy: technical innovations and evolving clinical applications

Myocardial perfusion scintigraphy (MPS) with single photon emission CT (SPECT) has served the cardiology community for almost three decades. Significant developments have taken place over recent years covering almost every aspect of the technique. This article describes the technical innovations in scanners, software, imaging protocols and stress regimens and discusses its evolving clinical role. Planar MPS was introduced in the 1970s. Two decades later, most centres have adopted SPECT with ECG gating for the combined assessment of myocardial perfusion and left ventricular function using thallium-201, technetium-99m-sestamibi or technetium-99m-tetrofosmin. Over the past few years MPS has evolved from a diagnostic test of high accuracy for the detection of coronary artery disease (CAD) (mean sensitivity and specificity 90% and 75%, respectively) to an important tool for risk stratification, for which a large body of evidence exists documenting its clinical value and cost-effectiveness in a broad range of patient subgroups.1–3 Recent innovations in the field are likely to enhance the value of MPS even further. Here we discuss the most important of these new developments. A new generation of cameras has been developed that exhibits a remarkably high sensitivity compared with conventional gamma camera systems. These are steady-state ‘small-footprint’ cameras that use new cadmium zinc telluride (CZT) detector technology. In contrast to traditional sodium iodide (NaI) detectors, CZT detectors can translate photon energy and location directly into electronic pulses without the need for photomultiplication of scintillation events. The D-SPECT camera (Spectrum Dynamics, Caesarea, Israel) comprises nine rotating pixilated detector columns of …

Quality assurance in myocardial perfusion tomography: A collaborative BNCS/BNMS audit programme

The aim of this study was to assess the status of acquisition and reporting of myocardial perfusion tomography in the UK. Centres were asked to provide an expert panel with clinical and technical information, digital and hard copy of raw data and reconstructed tomograms, as well as their report (optional) for five randomly selected studies. Ninety studies were received from 18 centres; report text was provided for 66 studies. Six parameters (stress technique, radiopharmaceutical usage, image acquisition and processing, report images and text) were scored as good (2), adequate (1) or poor (0) by consensus. Centres received the quality scores for each study and a consensus clinical report from the panel. Stress technique was scored as inadequate in 10 (11%) studies, radiopharmaceutical usage and image acquisition as inadequate in 5 (6%) studies, image processing as inadequate in 8 (10%) studies and report images as inadequate in 2 (3%) studies. Report text was felt to be inadequate in 21 of 66 (32%) studies; in 11 of these (52%), the report text was judged to be incorrect and in 10 (48%) it was essentially correct but misleading because of poor phraseology. The mean quality score per study was 1.3 (range 0.5-2.0). Seventeen of 88 (19%) studies scored less than 1.0 and were considered to be of poor quality. In conclusion, a large variation in standards of myocardial perfusion tomography was seen. Data acquisition was generally satisfactory, but 32% of reports were inadequate.

Pitfalls and artifacts using the D-SPECT dedicated cardiac camera

Myocardial perfusion imaging is a well-established and widely used imaging technique for the assessment of patients with known or suspected coronary artery disease. Pitfalls and artifacts associated with conventional gamma cameras are well known, and the ways to avoid and correct them have been described. In recent years solid-state detector dedicated cardiac cameras were introduced and have been shown to offer improved accuracy in addition to new imaging protocols and novel applications. The purpose of this manuscript is to familiarize the readers with the causes and effects of technical, patient-related, and operator-related pitfalls and artifacts associated with the D-SPECT dedicated cardiac camera with solid-state detectors. The manuscript offers guidance on how to avoid these factors, how to detect them, and how to correct better for them, providing high-quality diagnostic images.