Rapid-acquisition myocardial perfusion scintigraphy (MPS) on a novel gamma camera using multipinhole collimation and miniaturized cadmium-zinc-telluride (CZT) detectors: prognostic value and diagnostic accuracy in a 'real-world' nuclear cardiology service.

AIMS: To study the prognostic value of rapid-acquisition adenosine stress-rest myocardial perfusion scintigraphy (MPS) on a gamma camera using multipinhole collimation and cadmium-zinc-telluride (CZT) detectors. The secondary aim was to assess the diagnostic accuracy of the technique compared with invasive coronary angiography. METHODS AND RESULTS: Retrospective analysis of 1109 consecutive patients undergoing MPS in a routine clinical setting on a high-efficiency multipinhole gamma camera. MPS acquisition, performed with a standard injection of 550 MBq of (99m)Tc-tetrofosmin, required a mean (±SD) scanning time of 322 ± 51 s. The hard cardiac event rate at a median (inter-quartile range) follow-up of 624 (552-699) days was 0.4% (95% CI 0.1-1.1) in patients with no significant perfusion abnormality versus 6.8% (95% CI 4.3-10.7%, P < 0.001) in those with an abnormal scan. In a sub-group of 165 patients, comparison with obstructive coronary artery disease on X-ray angiography gave a sensitivity, specificity, positive predictive value, negative predictive value, and accuracy for rapid-acquisition MPS of 84% (95% CI 74-91), 79% (95% CI 68-87), 82% (95% CI 72-89), 81% (95% CI 70-89), and 82% (95% CI 73-89), respectively. CONCLUSIONS: MPS performed on a CZT solid-state detector camera with multipinhole collimation is an evolutionary development that provides reliable prognostic and diagnostic information, while significantly reducing image acquisition time.

Comparison of 99mTc tetrofosmin gated SPECT measurements of left ventricular volumes and ejection fraction with MRI over a wide range of values.

The calculation of ejection fraction using gated single photon emission computed tomography (SPECT) has been widely validated against a range of other techniques. There have been fewer studies validating left ventricular volumes. We compared quantitative gated SPECT (QGS) with magnetic resonance imaging (MRI) measurements of left ventricular ejection fraction and end diastolic volume in 50 patients with a large range of ventricular dimensions. MRI data were obtained using a turbo gradient echo pulse sequence (TGE) in 17 patients and a steady state free precession pulse sequence (SSFP) in 33 patients. There was good correlation between ejection fraction and end diastolic volume measurements from SPECT and MRI (r=0.82, r=0.90, respectively) but the mean SPECT values were significantly lower (ejection fraction, 6.6+/-6.4% points; end diastolic volume, 18.4+/-25.4 ml) than those obtained from MRI. Bland-Altman analysis showed some large differences in individual patients but no trends in the data either in ejection fraction over a range from 15% to 70% or in end diastolic volume, range 75-400 ml. SSFP gave a larger difference for end diastolic volume measurement compared to SPECT than did TGE, although this difference did not reach significance. Both SSFP and TGE gave similar values for the difference between MRI and SPECT for the measurement of ejection fraction. We suggest that the difference in EF may be a result of 8 frames being used for gating in QGS but 12-18 for MR. Differences in volumes may be related to the different spatial resolution and the exclusion or inclusion of trabeculation and papillary muscles between SPECT and MRI. Differences between SSFP and TGE may be caused by differing delineation of the endocardial border, dependent on the particular acquisition sequence. In conclusion, QGS values correlated well with MRI, but a correction factor may be needed if direct comparison is made.

A survey of the role of the UK physicist in nuclear medicine: a report of a joint working group of the British Institute of Radiology, British Nuclear Medicine Society, and the Institute of Physics and Engineering in Medicine.

Guidelines for the provision of physics support to nuclear medicine were published in 1999 by a joint working group of the British Institute of Radiology, the British Nuclear Medicine Society, and the Institute of Physics and Engineering in Medicine. Following publication of the guidelines, a survey was conducted by the working group to gather data on the actual level of physicist support in UK hospitals of different types and on the activities undertaken by physicists. The data were collected in the 12 months following the publication of guidelines and cover different hospital models and seven UK regions. The results provide evidence that many of the smaller units - small teaching hospitals and, particularly, small district general hospitals - have insufficient physics support. Although, on average, there is good agreement between the guidelines and the survey data for medium and large district general hospitals, there is wide variation in the level of physics provision between hospitals delivering apparently similar services. This emphasizes the need for national guidelines, against which institutions may be bench-marked and which may be used as a recommendation for the staffing levels necessary to ensure services are delivered safely and standards are not compromised. The complexity and variety of workload is an important factor in determining the level of physics support. As services develop, it is vital that this aspect is recognized to ensure that appropriate resources are available for the required physics input, even if any new service represents only a modest clinical throughput in terms of patient numbers.

Assessment of adenosine, arbutamine and dobutamine as pharmacological stress agents during (99m)Tc-tetrofosmin SPECT imaging: a randomized study.

We evaluated the use of adenosine, dobutamine and arbutamine with (99m)Tc-tetrofosmin myocardial perfusion imaging. Forty patients under investigation for suspected coronary artery disease were recruited. Each had a resting scan and two separate stress scans on different days, in a randomized cross-over study. Resultant images were blindly reported in 13 segments per scan as normal, reversible or fixed defects. A score was given (0-3) for segmental defect severity. Haemodynamic responses were as expected for each agent. Subjective side effect scores did not differ overall between agents. Adenosine caused a significantly higher incidence of abnormal taste (54%) than dobutamine and arbutamine (both 23%) and a lower incidence of palpitations (25% vs 69% and 54%, respectively), all P<0.05. Arbutamine caused significantly more chest pain than adenosine (77% vs 46%) though less flushing (35% vs 68%), both P<0.05. Comparison of the results obtained showed highly significant levels of segmental agreement for visual and semi-quantitative analysis between adenosine and arbutamine, kappa value and correlation coefficient of 0.78 and 0.86, respectively, dobutamine and adenosine 0.69 and 0.78, and arbutamine and dobutamine 0.75 and 0.78, all P<0.0001. Adenosine, arbutamine and dobutamine differ in their haemodynamic response and side effect profile but provide highly comparable results during (99m)Tc SPECT imaging.

18FDG SPECT to assess myocardial viability: initial experience at a hospital remote from a cyclotron.

18F-Fluorodeoxyglucose positron emission tomography (18FDG PET) is the recognized gold standard for the assessment of myocardial viability, but is not widely available in the UK. FDG imaging on a gamma camera with high-energy collimators (FDG SPECT) has been shown to have an accuracy comparable with that of FDG PET for the assessment of myocardial viability. This study was performed to assess the feasibility of introducing FDG SPECT for myocardial viability at a hospital a considerable distance away from a cyclotron (200 miles). Twenty-three patients, who were being actively considered for revascularization but had demonstrated fixed defects on stress/rest with nitrate tetrofosmin imaging, underwent FDG SPECT. Image quality was acceptable in all patients. Nine out of the 23 patients with defects classed as fixed on tetrofosmin imaging demonstrated viability on FDG SPECT. Six of these nine patients, reported to have some viable myocardium on FDG SPECT, underwent revascularization as a result. This study has demonstrated that FDG SPECT is feasible at a site some distance from a cyclotron.

The routine use of sublingual GTN with resting 99Tcm-tetrofosmin myocardial perfusion imaging.

Nitrates can be used to improve resting myocardial blood flow in patients with severe coronary artery disease. This may enhance tracer uptake during rest myocardial perfusion imaging. Recent studies using nitrates at rest have shown increased detection of reversible ischaemia in this patient group with the 201Tl and 99Tcm perfusion tracers MIBI and tetrofosmin. However, it is not always possible to assess the severity of coronary artery disease before the rest injection and therefore whether a patient would benefit from nitrate administration. To improve the sensitivity for the detection of reversible ischaemia and to avoid a repeat study with nitrates (especially in patients with 'fixed' defects), a protocol in which all patients routinely receive nitrates prior to the rest injection is required. This prospective study evaluated the effect of nitrate administration prior to rest imaging in a randomly selected group of patients. Thirty patients selected at random from routine referrals had stress, rest and rest + GTN tetrofosmin imaging on three separate days. Changes in reversibility between the rest and rest + GTN images were assessed both visually and using semi-quantitative analysis. Defects at stress were seen in 43 coronary artery territories, 33 of which were reversible at rest and 37 reversible at rest + GTN. Of these 43 defects, 82% demonstrated either increased or the same degree of reversibility at rest + GTN imaging compared to standard rest imaging. All defects with reduced reversibility at rest + GTN imaging (i.e. the remaining 18%) were, however, still reversible compared to the stress images. Some of this reduced reversibility may be due to attenuation artefacts. We conclude that the routine use of GTN with rest tetrofosmin imaging will result in increased detection of ischaemic areas with no loss of sensitivity or specificity.

The use of GTN to improve the detection of ischaemic myocardium using 99Tcm-tetrofosmin.

Recent work has shown that rest 99Tcm-sestamibi uptake may underestimate the amount of perfused myocardium, suggesting infarct tissue in some instances when myocardium is hypoperfused but which will benefit from revascularization. Administration of nitrates before a resting 99Tcm-sestamibi injection has been shown to increase tracer uptake. We have used 99Tcm-tetrofosmin as a myocardial perfusion agent and imaged 30 patients at stress, rest and again at rest following administration of sublingual nitrates. All patients had angiographically demonstrated severe coronary artery disease and 27 patients had previous infarction. Twenty-one patients were stressed on a treadmill and nine using intravenous dobutamine. Images were analysed using both a visual and semi-quantitative analysis. Defects were observed in 39 coronary artery territories on stress 99Tcm-tetrofosmin imaging, 23 appearing fixed on standard rest imaging. Twelve (52%) of these defects showed reversibility on rest with glyceryl trinitrate (GTN) imaging and increased reversibility was seen in 62% of defects reversible at rest. We conclude that, in patients with severe coronary artery disease and fixed rest defects, GTN given prior to the rest injection appears to improve the detection of ischaemic hypoperfused myocardium.

Evaluation of 99Tcm-tetrofosmin as a myocardial perfusion agent in routine clinical use.

Recent trials with selected patients have indicated that 99Tcm-tetrofosmin is a suitable agent for myocardial perfusion imaging. We performed 99Tcm-tetrofosmin perfusion imaging in an unselected group of 297 patients routinely referred to our department. Single photon emission tomographic (SPET) imaging was performed 45-60 min post-injection using a 2-day stress and rest protocol. Altogether, 192 patients were stressed on a treadmill and 105 using intravenous dobutamine. Comparison with angiography was possible in 86 patients, 65 of whom had atheromatous coronary artery disease and 21 of whom had normal coronary arteries (6 of whom fulfilled the criteria for syndrome X). The sensitivity for the detection of coronary artery disease was 94% (93% for exercise stress and 95% for dobutamine). The overall specificity was 85% (87% for exercise stress and 80% for dobutamine in the 15 normal patients and the segments supplied by disease-free coronary vessels in patients with disease elsewhere). We conclude that 99Tcm-tetrofosmin is a highly sensitive and specific agent for the detection of coronary artery disease, using both exercise and dobutamine stress, with few limitations.

Percutaneous transluminal angioplasty of the tibial arteries.

To evaluate the results of percutaneous transluminal angioplasty (PTA) of the tibial vessels, results of 50 procedures performed in 38 patients since 1988 were analysed retrospectively. A total of 73 tibial vessels were treated: 32 anterior tibial arteries, 16 posterior tibial arteries, four peroneal arteries, 12 tibioperoneal trunks and nine trifurcation lesions. Forty-four of 50 PTA procedures were performed in conjunction with interventions in the femoropopliteal arteries and six as isolated procedures. One patient required a femorodistal graft following perforation of the popliteal artery during atherectomy. Distal emboli occurred in two patients and acute thrombosis of both the angioplastied tibial vessels occurred in a third. The technical success rate was 96 per cent. Patients were followed for a mean(s.d.) of 21(13) months. At the latest follow-up, 58 per cent had improved clinically. There were significant improvements in 43 per cent of limb isotope blood flow studies and 52 per cent of ankle:brachial Doppler pressure indices in treated limbs at this time. PTA should be the first treatment option in patients with infrapopliteal arterial disease needing intervention, whenever it is technically feasible.

Limb blood flow measurement in technically successful balloon angioplasty.

An isotope limb blood flow technique was used to assess the outcome of technically successful balloon angioplasty. Measurements were made on a total of 120 limbs, before angioplasty and at least once after angioplasty at 3 weeks, 3 months, 6 months, 12 months and 2-5 years. 67% of treated limbs showed a significant improvement in limb blood flow at 3 weeks. At 12 months following angioplasty 43% of limbs still showed an improvement in blood flow compared with the measurement made before angioplasty. However, a number of these limbs showed a significant fall in limb blood flow between 3 weeks and 12 months even though the 3 week and the 12 month flow figures were still greater than those before angioplasty. The degree of initial improvement in blood flow seen at 3 weeks persisted at 12 months after angioplasty without significant fall in only 30% of limbs. In 33% of limbs where the balloon angioplasty was technically successful there was no improvement in blood flow at 3 weeks. 80% of these limbs had further significant untreated disease angiographically, compared with 43% of limbs where there was an increase in limb blood flow.

Does peripheral angioplasty compromise limb blood flow?

Isotope limb blood flow studies were carried out using balloon, laser and Kensey catheter techniques to assess the outcome of peripheral angioplasty. Limb blood flow and Doppler ankle-brachial pressure measurements were obtained before angioplasty and at 6 months after angioplasty in a total of 101 angioplastied limbs: A fall in limb blood flow at 6 months was seen in 17% of the angioplastied limbs with no significant difference in the figures for the different types of angioplasty. Limb blood flow was also measured in 53 contralateral untreated limbs, approximately half of the patient group having both legs angioplastied. 25% of untreated limbs showed a fall in limb blood flow. Significantly more of the untreated limbs showed a fall in limb blood flow at 6 months where the contralateral, treated limb did not improve as a result of the angioplasty compared with those patients where the angioplastied leg improved. These results suggest that a lack of improvement in blood flow in the angioplastied limb may not result from failure of the angioplasty but may be the result of some factor, or combination of factors, which adversely affects both the angioplastied and the untreated leg in some patients.

A comparison of methods for estimating left ventricular volumes from radionuclide ventriculography.

An accurate reproducible measurement of left ventricular volume is important in the evaluation of cardiac disease. Four methods of left ventricular volume measurement by radionuclide ventriculography have been compared and their reproducibility assessed in a patient group. The methods studied were a geometric method, a method based on count data alone and two methods which require a blood sample and an estimate of ventricular depth. The accuracy of absolute volumes is difficult to determine due to the lack of a 'gold standard'. The method using count data alone was found to give reproducible results. Volumes can be calculated quickly and easily from data acquired in a standard radionuclide ventriculogram. End systolic volumes calculated using this method clearly separated normal and abnormal patient groups.

The use of dobutamine stress thallium scintigraphy in the diagnosis of syndrome X.

Dobutamine stress thallium scintigraphy is a non-exercise stress technique used in the assessment of myocardial ischaemia. Non-exercise techniques are independent of the patient's exercise capacity or the subjective development of limiting symptoms. Preliminary data are presented regarding the effects of graded infusions of dobutamine (maximum 20 micrograms/kg/min) in seven consecutive patients with syndrome X. The dobutamine stress test caused significant increases in mean heart rate (rest 65.4 beats/min, peak dobutamine infusion 112.4 beats/min, P < 0.001) and systolic blood pressure (rest 138.6 mmHg, peak dobutamine infusion 166.7 mmHg, P = 0.002) and provoked typical symptoms in all the patients. Single photon emission computerized tomography was performed and the mean number of reversible defects was 1.86 per patient (range 1-3). One patient developed transient atrial fibrillation during the dobutamine infusion but there were no complications in the remainder of the study group. It is concluded that dobutamine-thallium scintigraphy in patients with syndrome X is safe, reproduces patients symptoms' reliably and presents a controllable degree of stress to the cardiovascular system. The consistent demonstration of a reversible perfusion defect in patients with syndrome X is evidence of abnormal myocardial physiology. This criterion could be added to those currently used to define syndrome X in order to improve objectively the identification of this patient group.

24-hour survival of autotransfused red cells in elective aortic surgery: a comparison of two intraoperative autotransfusion systems.

Twelve patients undergoing elective aortic surgery had intraoperative autotransfusion using either the Haemonetics Cell Saver or the Solcotrans device. The 24-h post-transfusion survival of the patients' preoperative red cells, labelled with indium-111, was compared with the survival of salvaged red cells labelled with chromium-51. A correction coefficient for the instability of the indium-111 label was calculated from the study of red cell survival in six healthy volunteers. There was no significant difference in the volume of circulating red cells measured using each isotope, indicating that extensive early destruction of the autotransfused red cells does not occur. The percentage survival of autotransfused red cells at 24 h was similar to that of the red cells that had not undergone salvage. Both devices were comparable with respect to the effects of cell salvage on the 24-h survival rate of autotransfused red cells.

Dual tracer technique to measure salvaged red cell survival following autotransfusion in aortic surgery.

The survival of autotransfused red cells was measured for two salvage devices used in 12 elective aortic reconstructions. Six patients underwent cell salvage with the Solco-trans device and six with the Haemonetics cell saver. A double tracer technique was used to take account of post-operative blood loss and fluid replacement. Comparison was made with the results of a group of normal volunteers. A comparison was made of the labelling efficiency of damaged and undamaged red cells using chromium to check that red cells damaged during autotransfusion can be labelled. No significant difference was seen. There was no significant difference in red cell survival between the volunteer group and either of the two salvage device groups. These results suggest that red cell survival is not compromised by the autotransfusion process using these two devices.