The absent kidney in 99Tcm-MAG3 renogram: a dramatic reversible consequence of contrast nephrotoxicity superimposed on renal obstruction.

99Tcm-mercaptoacetyltriglycine (MAG3) renogram is a robust imaging technique used to delineate upper urinary tract obstruction. The changes observed on the renogram are often reversible on relief of obstruction. We present two cases illustrating the extreme consequence of contrast nephrotoxicity on pre-existing obstructed kidneys. In one case, this led to severe impairment of perfusion and uptake observed on 99Tcm-MAG3 renogram and in the second case virtual non-visualization of the obstructed kidney. Subsequent treatment of obstruction, led to dramatic improvement in renal function. It is important for clinicians, nuclear medicine physicians and radiologists to be aware of the potential of contrast nephrotoxicity in obstructed kidneys.

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.

Influence of arm positioning on tomographic thallium-201 myocardial perfusion imaging and the effect of attenuation correction.

Lateral attenuation in single-photon emission tomography (SPET) myocardial perfusion imaging (MPI) has been attributed to the left arm if it is held by the patient's side during data acquisition. As a result MPI data are conventionally acquired with the arms held above the head. The aims of this study were to determine the effect of imaging arms down on reconstructed tomographic images depicting regional myocardial thallium-201 distribution and to assess whether attenuation-corrected (AC) myocardial perfusion images acquired arms down could replace uncorrected (NC) images acquired arms up for routine clinical service. Twenty-eight patients referred for routine MPI underwent sequential 180 degrees emission/transmission imaging for attenuation correction using an L-shaped dual-headed gamma camera (GE Optima) fitted with two gadolinium-153 scanning line sources. Delay data were acquired twice: once supine with the arms up and then supine with the arms down. Detector radius of rotation (ROR) for arms up and arms-down studies was recorded. For each data set, count density was measured in 17 segments of a polar plot and segmental uptake expressed relative to study maximum. Oblique images were assessed qualitatively by two observers blinded to study type for tracer distribution and overall quality. Transmission maps were assessed for truncation. Mean detector ROR was 190 mm for arms-up studies and 232 mm for arms-down studies (P<0.05). Population mean segmental relative uptake values for NC arms-up studies were higher than for NC arms-down studies, with the greatest difference seen anterolaterally. Nevertheless, the majority (24/28) of oblique NC arms-up and NC arms-down images appeared similar and only four (14%) NC arms-down studies showed additional areas of reduced count density (one anterior and three lateral). Corresponding AC arms-down studies showed that count density within the anterior defect improved to normal but the lateral reductions persisted, and in two of these three studies the arms-down transmission map was distorted. Population mean segmental relative uptake values for NC arms-down studies were lower than for AC arms-down studies apart from three anterolateral segments where NC arms-down values were higher. Of 28 AC arms-down studies, 11 (39%) were of reduced quality compared with NC arms-up studies because of poorer spatial resolution and because AC enhances liver activity compared with NC. It is concluded that arm positioning influences reconstructed tomographic images depicting regional 201T1 distribution, particularly anterolaterally. There is lateral undercorrection in approximately 10% of AC arms-down studies, possibly because of attenuation map truncation. Image quality is reduced in about one-third of AC armsdown studies compared with NC arms-up studies. These data suggest that this attenuation correction method is not sufficiently robust to allow routine acquisition of MPI data with the arms down.

Radionuclide imaging of the heart.

Nuclear cardiology is an established part of diagnosis and assessment of patients with possible heart disease, the two most common tests being myocardial perfusion imaging and radionuclide ventriculography. Myocardial perfusion imaging comprises approximately 75% of nuclear cardiology studies in the UK, and is used in diagnosis and management of coronary artery disease.

Iodine-131-MIBG therapy of a patient with carcinoid liver metastases.

UNLABELLED: Iodine-13I-metaiodobenzylguanidine (MIBG) is highly concentrated by >60% of carcinoid metastases and thus provides a therapeutic opportunity. METHODS: A symptomatic patient with carcinoid liver metastases, unresponsive to chemotherapy combined with interferon-alpha, was subsequently treated with 131I-MIBG. RESULTS: Radionuclide therapy, which was without significant side effects, resulted in symptomatic improvement and reduced urinary 5-hydroxyindoleacetic acid levels. No new metastases were observed for 15 mo after 131I-MIBG therapy. Gross cystic change occurred in existing liver metastases, presumably as a result of ischemic necrosis. Surgical deroofing and aspiration of cysts led to regeneration of normal liver tissue. CONCLUSION: Iodine-131-MIBG therapy can provide prolonged symptomatic relief and improved quality of life in patients with metastatic carcinoid disease unresponsive to other therapies. The antitumor effect of 131I-MIBG was accompanied by few side effects, suggesting that this therapy should be considered in symptomatic patients with an early stage of disease.

Quality assurance in myocardial perfusion tomography: a collaborative BNCS/BNMS audit programme. British Nuclear Cardiology Society/British nuclear Medicine Society.

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.

Clinical evaluation of technetium-99m-L,L-ethylenedicysteine in patients with chronic renal failure.

UNLABELLED: Technetium-99m-L,L-ethylenedicysteine (99mTc-L,L-EC), a new renal radiopharmaceutical, has been shown to have similar excretion characteristics but a higher plasma clearance than 99mTc-mercaptoacetyltriglycine (99mTc-MAG3) in normal volunteers and patients with obstructive nephropathy. This study evaluated 99mTc-L,L-EC in patients with chronic renal failure. METHODS: The clearance of 99mTc-L,L-EC was compared with that of 125l-hippuran in 26 patients with varying degrees of chronic renal impairment (serum creatine 168-1163 mumol/liter). All 26 patients also were imaged with 99mTc-L,L-EC (70-80 MBq). Fifteen patients had further imaging with 99mTc-MAG3 (100 MBq) the following day. RESULTS: A subjective analysis of the 99mTc-L,L-EC images revealed that all were of acceptable quality regardless of creatinine level. In the 15 patients who were imaged with both 99mTc-L,L-EC and 99mTc-MAG3, general image quality and target-to-background ratios were similar. Time-activity curves and mean parenchymal transit times obtained with the two agents were almost identical. Plasma clearance values (mean +/- s.d.) of 99mTc-L,L-EC and 125l-hippuran were 81 +/- 68 ml/min and 114 +/- 104 ml/min, respectively. Mean 99mTc-L,L-EC clearance was 71% of the mean 125l-hippuran value. CONCLUSION: Technetium-99m-L,L-EC provides equally high-quality images to 99mTc-MAG3 in patients with chronic renal failure. Technetium-99m-L,L-EC clearance more closely resembles that of hippuran than does 99mTc-MAG3 clearance. These features together with its ease of preparation make 99mTc-L,L-EC an attractive alternative to 99mTc-MAG3 in patients with chronic renal failure.

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 myocardial 201T1 distribution in patients with low risk of coronary artery disease. An L-shaped dual-detector 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.

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.

Gallium-67 imaging of pericardial lymphoma in AIDS.

A 33-yr-old homosexual man with acquired immune deficiency syndrome (AIDS) and Mycobacterium avium intracellulare (MAI) infection presented with fever, sweats, lethargy and dyspnea. A chest radiograph showed cardiomegaly and an echocardiograph revealed a large pericardial effusion. After pericardial aspiration, which confirmed T cell non-Hodgkin's lymphoma, he remained dyspneic. Gallium-67 imaging was performed to determine whether the patient's residual dyspnea was related to pulmonary MAI infection or lymphomatous infiltration of the heart. Planar 67Ga scintigraphy revealed intense tracer uptake in two areas within the mediastinum and surrounding the entire heart shadow but no evidence of pulmonary MAI infection. SPECT 67Ga scintigraphy precisely localized the two mediastinal abnormalities and demonstrated the tracer uptake around the heart to be pericardial rather than myocardial. Gallium-67 scintigraphy suggested that pericardial lymphoma was the likely basis of the patient's dyspnea.

The role of nuclear medicine in the investigation of patients with AIDS.

HIV-positive patients are susceptible to both opportunistic infection and malignant disease. Radionuclide techniques can help in the detection of the occult infection and in the differentiation between infection and tumour.

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

The 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 lack 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.

Identification of reversible ischaemia after acute myocardial infarction using thallium tomography with early and delayed imaging after resting injection.

We studied 30 patients 6 weeks after first myocardial infarction in order to compare early and delayed imaging after resting injection of thallium for the detection of viable myocardium. Twenty-six of the 30 patients studied had received thrombolysis. Conventional stress and redistribution thallium tomography was followed by a resting injection of thallium with imaging immediately after in all patients and 3 h later in a subgroup of 15 patients. Thallium uptake was graded semi-quantitatively in each of nine myocardial segments. Eighty-eight of the 270 segments had a fixed defect on redistribution imaging, 40 (45%) of which had improved uptake in the immediate reinjection images. Only 9 of 135 (6%) segments with fixed defects on immediate reinjection imaging showed additional uptake with delayed reinjection imaging. These data suggest that imaging early after thallium reinjection is of value in the detection of reversible ischaemia after infarction, but that delayed reinjection imaging offers little additional benefit.

Improved assessment of inferior left ventricular wall motion using biplane equilibrium radionuclide ventriculography.

Equilibrium radionuclide ventriculography is often restricted to the left anterior oblique projection. The differential sensitivity of left anterior oblique amplitude and phase images for anterior and inferior infarction was evaluated using quantitative analysis, and the role of left posterior oblique images assessed. Twenty anterior infarcts, 20 inferior infarcts and 20 normal controls were studied. Left anterior oblique amplitude and phase abnormalities were seen in 100% (20) and 85% (17) of anterior infarcts but only 55% (11) and 50% (10) of inferior infarcts. Left posterior oblique amplitude and phase abnormalities were seen in 95% (19) of anterior infarcts and 75% (15) and 85% (17) of inferior infarcts. Left anterior oblique standard deviation of phase differed from normal only for anterior infarction (P < 0.01); both anterior and inferior (P < 0.05) infarction differed from normal in the left posterior oblique projection. Left anterior oblique images are therefore insensitive for inferior infarction. An accurate description of regional ventricular wall motion requires biplane radionuclide ventriculography.