Quantitative SPECT/CT parameters of myocardial 99mTechnetium-3,3-diphosphono-1,2-propanodicarboxylic acid (DPD) uptake in suspected cardiac transthyretin amyloidosis.

BACKGROUND: 99mTc-labelled bisphosphonates are used for imaging assessment of patients with transthyretin cardiac amyloidosis (ATTR). Present study evaluates whether quantitative SPECT/CT measurement of absolute myocardial 99mTc-labelled 3,3-diphosphono-1,2-propanodicarboxylic acid (Tc-DPD) uptake can diagnose patients with suspected ATTR. METHODS: Twenty-eight patients (25 male, age 80.03 ± 6.99 years) with suspected ATTR referred for Tc-DPD imaging had planar and SPECT/CT imaging of the chest. Three operators independently obtained Tc-DPD myocardial SUVmax and SUVmean above threshold (SMaT) (20, 40 and 60% of SUVmax), using a semi-automated threshold segmentation method. Results were compared to visual grading (0-3) of cardiac uptake. RESULTS: Twenty-two patients (78%) had cardiac uptake (2 grade 1, 15 grade 2, 5 grade 3). SUVmax and SMaT segmentation thresholds enabled separating grades 2/3 from 0/1 with excellent inter- and intra-reader correlation. Cut-off values 6.0, 2.5, 3 and 4 for SUVmax, SMaT20,40,60, respectively, separated between grades 2/3 and 0 /1 with PPV and NPV of 100%. SMaT20,40,60(cardiac)/SUVmean (liver) and SMaT20,40,60(cardiac)/SUVmean(liver/lung) separated grades 2 and 3. CONCLUSION: Quantitative SPECT/CT parameters of cardiac Tc-DPD uptake are robust, enabling separation of patients with grades 2 and 3 cardiac uptake from grades 0 and 1. Larger patient cohorts will determine the incremental value of SPECT/CT quantification for ATTR management.

Paediatric Molecular Radiotherapy: Challenges and Opportunities.

The common contemporary indications for paediatric molecular radiotherapy (pMRT) are differentiated thyroid cancer and neuroblastoma. It may also have value in neuroendocrine cancers, and it is being investigated in clinical trials for other diseases. pMRT is the prototypical biomarker-driven, precision therapy, with a unique mode of delivery and mechanism of action. It is safe and well tolerated, compared with other treatments. However, its full potential has not yet been achieved, and its wider use faces a number of challenges and obstacles. Paradoxically, the success of radioactive iodine as a curative treatment for metastatic thyroid cancer has led to a 'one size fits all' approach and limited academic enquiry into optimisation of the conventional treatment regimen, until very recently. Second, the specialised requirements for the delivery of pMRT are available in only a very limited number of centres. This limited capacity and geographical coverage results in reduced accessibility. With few enthusiastic advocates for this treatment modality, investment in research to improve treatments and broaden indications from both industry and national and charitable research funders has historically been suboptimal. Nonetheless, there is now an increasing interest in the opportunities offered by pMRT. Increased research funding has been allocated, and technical developments that will permit innovative approaches in pMRT are available for exploration. A new portfolio of clinical trials is being assembled. These studies should help to move at least some paediatric treatments from simply palliative use into potentially curative protocols. Therapeutic strategies require modification and optimisation to achieve this. The delivery should be personalised and tailored appropriately, with a comprehensive evaluation of tumour and organ-at-risk dosimetry, in alignment with the external beam model of radiotherapy. This article gives an overview of the current status of pMRT, indicating the barriers to progress and identifying ways in which these may be overcome.

18F-Fluorodeoxyglucose positron emission tomography-computed tomography imaging in HIV-infected patients with lymphadenopathy, with or without fever and/or splenomegaly.

We audited whether 18F-Fluorodeoxyglucose positron emission tomography-computed tomography (18FDG PET-CT) imaging could discriminate between different diagnoses in HIV-infected patients presenting with lymphadenopathy, with or without fever and/or splenomegaly. Maximum standardised uptake (SUVmax) values were similar in lymphoma and mycobacterial and fungal infections and were lower but similar in those with human herpesvirus (HHV) 8-associated disease and HIV-associated reactive lymphadenopathy. Nodal 18FDG avidity, with SUVmax ≥10, excluded diagnoses of HHV 8-associated disease and miscellaneous conditions, and HIV-associated reactive lymphadenopathy was additionally excluded in those who had undetectable plasma HIV viral loads. This audit suggests 18FDG PET-CT imaging did not permit discrimination between specific diagnoses but has utility in identifying lymph nodes with increased avidity that could be targeted for biopsy and in ruling out significant pathology.

Radiation exposure to comforters and carers during paediatric molecular radiotherapy.

BACKGROUND: To show whether the incidental radiation exposure received by comforters and carers of children undergoing molecular radiotherapy was kept as low as reasonably achievable and was within English national dose constraints. PROCEDURE: The radiation exposure of adult comforters and carers was routinely monitored with a whole body personal dose meter while the child was in hospital. Data were collected on iodine-131 meta-iodobenzylguanidine (131 I-mIBG), lutetium-177 DOTATATE (177 Lu-DOTATATE), and iodine-131 sodium iodide (131 I-NaI) treatments. RESULTS: Data were available for 50 treatments with high-administered activity double-infusion 131 I-mIBG and 12 single administrations; 15 177 Lu-DOTATATE treatments and 28 131 I-NaI administrations. The median age was 7 years (1-18). The median administered activity of: 131 I-mIBG was 16.2 GBq (6.8-59 GBq) for double infusion patients and 8.1 GBq (5.26-16.25 GBq) for single administrations; 177 Lu-DOTATATE was 7.2 GBq (2.5-7.5 GBq); and 131 I-NaI was 3 GBq for thyroid remnant ablation and 5.5 GBq for cancer therapy. The median number of comforters and carers for all administrations was 2 (range 1-9). The median exposure values for comforters and carers for high-administered activity 131 I-mIBG administrations was 302 µSv (0-5282 µSv); for single fraction 131 I-mIBG 163 µSv (3-3104 µSv); 177 Lu-DOTATATE 6 µSv (1-79 µSv); and 131 I-NaI 37 µSv (0-274 µSv). Only one of the comforters and carers exceeded the dose constraint of 5 mSv. CONCLUSIONS: Doses to comforters and carers were in all but one case within the dose constraint nationally recommended by the Health Protection Agency, now part of Public Health England. New evidence is presented which show that comforter and carer radiation exposure levels from paediatric molecular radiotherapy in routine clinical practice are acceptably low. Pediatr Blood Cancer 2015;62:235-239. © 2014 Wiley Periodicals, Inc.

Can upright myocardial perfusion imaging be used alone with a solid-state dedicated cardiac camera?

AIM: The novel solid state dedicated cardiac cameras provide fast high resolution cardiac imaging. The D-SPECT camera enables semi-reclining (upright) positioning, increasing comfort and potentially reducing movement during myocardial perfusion imaging. Physicians are generally familiar with supine imaging and the different positioning in upright imaging could potentially cause diagnostic challenges. The aim of this study was to compare the upright and supine imaging for diagnostic ability to assess Physician confidence and determine any artefacts in upright imaging. METHODS: Fifty-five patients underwent myocardial perfusion imaging on the D-SPECT camera in both upright and supine positions. Where both images showed the same defects the 2 techniques were regarded as equally diagnostic. Where only one set showed a defect this was regarded as artefact and was defined as non-diagnostic. The location and cause of the artefact was recorded. RESULTS: In 13 /55 patients either form of imaging was regarded as equally diagnostic. In 24/55 the supine images revealed artefact affecting interpretation. The reasons for this were most frequently large BMI, motion and gut uptake. In 18/55 upright images were considered non-diagnostic. In 16/18 this was due to an infero-apical defect seen in female patients (14/16) with raised BMI and/or large breasts. CONCLUSION: Upright myocardial perfusion imaging on D-SPECT shows a common artefact (in up to 1/3 of cases) in the infero-apical region mainly in overweight female patients. Getting acquainted with this artefact this may increase Physician confidence in reporting, similarly as to conventional supine imaging. Indeed, some of the artefacts seen on supine imaging appear less commonly with upright imaging. Thus, upright imaging can potentially be used alone for diagnosis with D-SPECT. Performance of both supine and upright imaging can be reserved for overweight patients thereby minimizing impact on scanning time and clinical throughput in busy departments.

Optimization of molecular radiotherapy with [131I]-meta Iodobenzylguanidine for high-risk neuroblastoma.

Molecular radiotherapy with [131I]-meta Iodobenzylguanidine ([131I]-mIBG) for neuroblastoma has been in clinical use for nearly 30 years. In this time, its role has changed from being an exclusively palliative treatment to one where the intent of treatment is often curative. To achieve this, the treatment has been brought forward from the relapse setting, to the beginning as induction therapy, as a possibility for salvage of those with chemo-refractory disease or as part of consolidation schedules. With the routine use of hemopoietic support, higher than previously standard administered activities are now commonly used. Other attempts to improve outcomes include the concomitant use of chemotherapy and radiation sensitisers and novel formulations such as no-carrier added [131I]-mIBG. Unfortunately, none of these strategies has been evaluated in a randomized controlled trial, so whether the theoretical benefits of these innovative approaches are seen clinically remains a matter of conjecture. Despite the prevalent belief in using higher administered activities, dosimetry has been under-used, hampering the ability to detect the benefit of this strategy. To properly evaluate concepts aiming at the optimisation of molecular radiotherapy with [131I]-mIBG for high-risk neuroblastoma, careful dosimetry in well-designed randomized clinical trials is essential. Only in this way will it be possible for [131I]-mIBG to be used to its best advantage in the complex multimodality treatment schedules required for high-risk neuroblastoma.

18F-Fludeoxyglucose PET/CT in the evaluation of large-vessel vasculitis: diagnostic performance and correlation with clinical and laboratory parameters.

OBJECTIVE: To investigate the diagnostic performance of (18)F-fludeoxyglucose ((18)F-FDG) positron emission tomography (PET)/CT in patients with suspected large-vessel vasculitis and its potential to evaluate the extent and activity of disease. METHODS: 78 consecutive patients (mean age 63 years; 53 females) with suspected large-vessel vasculitis were evaluated with (18)F-FDG PET/CT.( 18)F-FDG uptake in the aorta and major branches was visually graded using a four-point scale and quantified with standardised uptake values (SUV(max)). According to clinical diagnosis, patients were classified into three groups: (a) steroid-naïve, large-vessel vasculitis (16 patients), (b) vasculitis on steroid treatment (18 patients) and (c) no evidence of vasculitis (44 patients). Analysis of variance and linear regression were used to investigate the association of (18)F-FDG uptake with clinical diagnosis and inflammatory markers. RESULTS: (18)F-FDG PET/CT was positive (visual uptake ≥ 2; equal to or greater than liver) in all patients with steroid-naïve, large-vessel vasculitis. The thoracic aorta, the carotid and the subclavian arteries were most frequently involved. In these patients, SUV(max) values were significantly higher than in the other groups (analysis of variance; p<0.05). Linear regression showed a significant positive association (b-coefficients: 0.018-0.02; p<0.05) between SUV(max) of the thoracic aorta and inflammatory markers in patients with vasculitis (Groups a and b). Patients on steroid treatment showed low visual scores (uptake <2) and significantly lower SUV(max) values than steroid-naïve patients. CONCLUSION: (18)F-FDG PET/CT can detect the extent and activity of large-vessel vasculitis in untreated patients and is unreliable in diagnosing vasculitis in patients on steroids.

99mTechnetium-mercaptoacetyltriglycine scintigraphy with full bladder in patients with severe bladder dysfunction.

PURPOSE: We evaluated 99mtechnetium-mercaptoacetyltriglycine scintigraphy for detecting threshold bladder volume at which upper tract obstruction occurs in patients with bladder dysfunction. MATERIALS AND METHODS: A total of 24 patients 19 to 74 years old with severe bladder dysfunction who underwent 99mtechnetium-mercaptoacetyltriglycine scintigraphy and videocystometrogram in a 4-year period were selected for retrospective study. 99mTechnetium-mercaptoacetyltriglycine scintigraphy was done with a full bladder with a mean instilled volume of more than 850 ml saline. In patients in whom an obstructed renal outflow pattern was observed saline was drained at a rate of 100 ml every 5 minutes while dynamic imaging was performed. If results were abnormal, the study was repeated with an empty bladder. Differential function, parenchymal transit time index and outflow efficiency were calculated. RESULTS: Of the 24 patients 15 had an obstructed outflow pattern with a full bladder, which was relieved at a bladder volume of less than 390 ml (median 300, range 250 to 600). Only 2 of these 15 patients had a normal vesical end filling pressure of less than 20 cm H2O. There was no obstruction in 9 patients, of whom 5 had increased vesical end filling pressures. Followup in patients who had normal tracer outflow on a full bladder showed no decrease in renal function, while a small decrease was seen in patients who had obstructed outflow on a full bladder. CONCLUSION: This novel, full bladder 99mtechnetium-mercaptoacetyltriglycine scintigraphic technique provides the ability to detect bladder volumes at which obstructive outflow patterns develop in patients with severe bladder dysfunction.

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.

Use of 18F-FDG positron emission tomography following allogeneic transplantation to guide adoptive immunotherapy with donor lymphocyte infusions.

Fluorine-18 fluorodeoxyglucose positron emission tomography ((18)F-FDG PET) provides valuable prognostic information in the management of lymphoma patients. However, the utility of (18)F-FDG PET following allografting is unclear. We analysed the use of (18)F-FDG PET after allogeneic reduced-intensity transplantation (RIT) performed in our institution. Between June 1998 and January 2002, 55 patients underwent RIT for either Hodgkin or non-Hodgkin lymphoma. At least one (18)F-FDG PET scan was performed during the post-transplant period (median five studies) in 15 (27.2%) of these 55 patients. PET scans were performed after re-staging computed tomography (CT) and were categorised depending on (18)F-FDG uptake. The first PET scan was informative in 11 of 15 patients (73%) and influenced the administration of donor lymphocyte infusions (DLI) in nine: leading to earlier DLI administration in two patients, earlier dose escalation in one, withholding of DLI administration in five and dose reduction in one. In addition, subsequent monitoring with (18)F-FDG PET scans documented a graft-versus-lymphoma effect in five patients (median post-DLI follow-up 33 months, range 13-36 months). These preliminary data suggest that (18)F-FDG PET has a role in guiding DLI administration and monitoring the immunotherapeutic effect in patients after allogeneic transplantation. This retrospective pilot study forms the basis for a prospective study to clarify the utility of (18)F-FDG PET/CT in these patients.

Impact of combined (18)F-FDG PET/CT in head and neck tumours.

To compare the interobserver agreement and degree of confidence in anatomical localisation of lesions using 2-[fluorine-18]fluoro-2-deoxy-D-glucose ((18)F-FDG) positron emission tomography (PET)/computed tomography (CT) and (18)F-FDG PET alone in patients with head and neck tumours. A prospective study of 24 patients (16 male, eight female, median age 59 years) with head and neck tumours was undertaken. (18)F-FDG PET/CT was performed for staging purposes. 2D images were acquired over the head and neck area using a GE Discovery LS PET/CT scanner. (18)F-FDG PET images were interpreted by three independent observers. The observers were asked to localise abnormal (18)F-FDG activity to an anatomical territory and score the degree of confidence in localisation on a scale from 1 to 3 (1=exact region unknown; 2=probable; 3=definite). For all (18)F-FDG-avid lesions, standardised uptake values (SUVs) were also calculated. After 3 weeks, the same exercise was carried out using (18)F-FDG PET/CT images, where CT and fused volume data were made available to observers. The degree of interobserver agreement was measured in both instances. A total of six primary lesions with abnormal (18)F-FDG uptake (SUV range 7.2-22) were identified on (18)F-FDG PET alone and on (18)F-FDG PET/CT. In all, 15 nonprimary tumour sites were identified with (18)F-FDG PET only (SUV range 4.5-11.7), while 17 were identified on (18)F-FDG PET/CT. Using (18)F-FDG PET only, correct localisation was documented in three of six primary lesions, while (18)F-FDG PET/CT correctly identified all primary sites. In nonprimary tumour sites, (18)F-FDG PET/CT improved the degree of confidence in anatomical localisation by 51%. Interobserver agreement in assigning primary and nonprimary lesions to anatomical territories was moderate using (18)F-FDG PET alone (kappa coefficients of 0.45 and 0.54, respectively), but almost perfect with (18)F-FDG PET/CT (kappa coefficients of 0.90 and 0.93, respectively). We conclude that (18)F-FDG PET/CT significantly increases interobserver agreement and confidence in disease localisation of (18)F-FDG-avid lesions in patients with head and neck cancers.

Treatment of neuroendocrine tumours in adults with 131I-MIBG therapy.

This is a retrospective review of 131I-MIBG therapy for metastatic neuroendocrine tumours in 25 adult patients. The tumours comprised 17 carcinoids, six paragangliomas, one somatostatinoma and one intestinal smooth muscle sarcoma. All patients (age range 28-84 years) had stage IV disease and a positive diagnostic 123I-MIBG scan. Patients received 11.1 GBq (300 mCi) of 131I-MIBG given in three cycles at 3-monthly intervals. The mean cumulative dose was 27.7 GBq (751 mCi). Symptomatic response was observed in 80%, hormonal response in 55% and tumour response in 48% (WHO criteria). Of the 25 patients, 40% are still under follow-up. Death was due to disease progression in all except one. The median survival time was 48 months from diagnosis of metastatic disease, and 17 months from the last 131I-MIBG therapy. The 5-year survival rate was 59% (95% confidence interval, 34%-78%). There was no statistical difference in survival between previously treated (chemo/radiotherapy) and treatment-naive patients. Side-effects were minimal and commonly include nausea (in the first 24 h) and a transient fall in platelet count. 131I-MIBG provides a good therapeutic response in patients with metastatic neuro-endocrine tumours.

99mTc sestamibi scintimammography in the diagnosis of palpable breast masses.

The aim of this prospective study was to evaluate the diagnostic performance of 99mTc sestamibi scintimammography in a region with a low incidence of breast cancer (East, central and West Africa) and to verify the clinical usefulness of this technique in identifying benign breast diseases. Thirty-eight women (age range 22-38 years) with palpable breast masses (n =38) and inconclusive mammograms were included. Prone scintimammography was performed 10 min and 60-90 min in all patients after injection using an isotime acquisition of 10 min. A positive scan for breast cancer was defined as tracer uptake on the 10 min image and retention of activity on the 60-90 min image. A negative scan was defined as uptake on the 10 min image and complete washout of activity on the 60-90 min image. All patients subsequently underwent excisional biopsy of the breast masses and histological confirmation of the pathology. The results of scintimammography and histopathology were in agreement in all patients, revealing 36 benign lesions and two malignant lesions. Histopathologically, the lesions were fibroadenomas (27), fibrocystic disease (five), abscesses (four) and invasive intraductal carcinoma (two). It is concluded that, in regions with high incidence of benign breast diseases in young women, 99mTc sestamibi scintimammography can be used to rapidly characterize benign and malignant breast masses and thereby give priority to the management of those with a serious condition.

Nuclear medicine in primary breast cancer imaging.

The application of nuclear medicine techniques to study patients with breast cancer has recently raised its profile, particularly in the investigation 'indeterminate mammographic lesions'. This review briefly points out some of the difficulties encountered with other more conventional imaging modalities and describes the radionuclide techniques most frequently employed in the investigation of those patients with breast cancer. Both planar and single photon emission tomography methods are discussed including the use of monoclonal antibodies, perfusion ligands, receptor binding hormones and other specific radiotracers, non-specific tumour markers, as well as deoxyglucose and other amino acids labelled with positron emitting radionuclides.

Functional imaging of malignant paragangliomas and carcinoid tumours.

Complete staging is mandatory for the management and therapy of neuroendocrine tumours. Various radiotracers are available but the best imaging strategy has yet to be defined. In this study we retrospectively compared 123I-MIBG, 111In-[D-Phe1]-DTPA-octreotide and 18F-FDG (PET) imaging in 15 patients with metastatic neuroendocrine tumours (11 carcinoid tumours, 4 paragangliomas). Planar images were acquired 1, 4, 24 and 48 h following the injection of 111In-[D-Phe1]-DTPA-octreotide and 123I-MIBG. Whole-body PET scans were performed 45 min after injection of 18F-FDG. 111In-[D-Phe1]-DTPA-octreotide was positive in 11/15 patients and identified 44 lesions, 18F-FDG PET was positive in 11/15 patients and identified 107 lesions and 123I-MIBG was positive in 8/15 patients and identified 67 lesions. No single scintigraphic technique identified all metastatic sites. In one patient all studies were negative. 18F-FDG PET identified more abnormal sites than the other two modalities. Combination of all three imaging modalities with X-ray CT helps to provide a more comprehensive map of the disease.

Functional imaging as an aid to decision-making in metastatic paraganglioma.

Malignant paraganglioma is a rare and slow growing tumour of neuroendocrine origin. At the time of diagnosis, the tumour is usually widespread, with limited therapeutic options. A variety of functional imaging studies are available for staging the disease, guiding therapy and monitoring treatment response. These include 123I-MIBG or 131I-MIBG, 111In-pentetreotide or 111In-lanreotide (somatostatin analogues), and 18F-FDG positron emission tomography. Various radionuclides, including 131I and 90Y, can be targeted to the tumour using MIBG or pentetreotide. Such targeted radionuclide therapy may provide valuable long-term palliation in such patients. We present two cases with metastatic paragangliomas who had widespread soft tissue and bone metastases. One patient was treatment naive and the second had received previous chemotherapy. The functional imaging work-up performed and the targeted radionuclide therapies considered in these patients are described. Both patients were treated with 131I-MIBG. Partial tumour response and complete symptomatic and hormonal response was achieved in one patient; in the second patient there was no change.

Clinical role of positron emission tomography in oncology.

Positron emission tomography (PET) is now in routine use in oncology, through the success of metabolic imaging, mainly with fluorodeoxyglucose (FDG). Clear benefit is obtained with FDG PET in the assessment of patients with recurrent or residual disease, especially colorectal cancer and lymphoma. Preoperative staging of non-small-cell lung cancer with FDG PET is of proven benefit. Staging and restaging of patients with melanoma of stage II or greater is useful, and FDG PET has also been successfully used to investigate single pulmonary nodules. Tumour grading has been assessed, especially in the brain, but an important and emerging indication is the evaluation of tumour response with PET. Rapid decline of FDG uptake has been observed in responsive cancers. Further advances are being made with other fluorine-18-labelled and generator-based PET tracers, the only ones that can be used in units without dedicated cyclotrons.

The clinical application of positron emission tomography to colorectal cancer management.

Colorectal cancer (CRC) is the second commonest cancer in the Western World. Successful treatment relies significantly on accurate detection and staging of primary disease as well as the early identification of the presence and extent of recurrence. Morphological imaging techniques, particularly computed tomography (CT), are well established and widely available to carry out these tasks in addition to predicting and monitoring response to therapy. This review analyses the current inadequacies for imaging CRC and critically assesses the potential role of functional imaging with positron emission tomography (PET). We review the current literature, use our experience from the first 1000 PET studies carried out at our Institution and the perspective of surgical colleagues. We find little evidence for the use of 2-[18F]fluoro-2-deoxy-D-glucose (FDG)-PET for screening asymptomatic individuals and current modalities appear better suited for detection of symptomatic primary CRC. There is evidence of increased accuracy for FDG-PET in staging primary disease, but this area remains controversial and larger studies are necessary. The situation is quite the reverse with respect to imaging suspected recurrent disease with FDG-PET being more sensitive and specific than conventional techniques. This benefit manifests itself through alteration in patient management and results in cost savings. PET also appears to have a specific place in the evaluation of patients undergoing radiotherapy and chemotherapy, a role that will expand. The evidence suggests that PET will ultimately become routinely incorporated into CRC patient management algorithms. Technological advances coupled with novel tracer research will facilitate this.

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.