M. C. Prescott

Attenuation correction of myocardial Spect studies using low resolution computed tomography images

ObjectivesArtefacts caused by tissue attenuation can create problems in the interpretation of myocardial perfusion studies. This study aimed to determine if attenuation correction using the ‘Hawkeye’ low-resolution X-ray computed tomography facility attached to a GE Millennium VG gamma camera reduced attenuation artefacts in our patient group. This technique offers potential advantages over isotope transmission methods of attenuation correction because of the lack of noise in the transmission images. MethodsNinety-four patients (64 males, 30 females) underwent stress/rest myocardial perfusion imaging using 99mTc tetrofosmin (188 studies). Semi-quantitative analysis of the attenuation corrected and non-corrected perfusion images was carried out using proprietary software (Emory ECToolbox). ResultsNo significant differences between attenuation corrected and non-corrected images were seen in the septal, lateral or apical segments. Attenuation correction produced a significant reduction in the defect scores in the inferior segment indicating the presence of attenuation artefacts. This was more marked in male patients. The incidence of attenuation artefacts in the inferior segment increased with weight although patients of normal weight also showed attenuation artefacts. The changes in the anterior segment were more difficult to interpret particularly in females, with attenuation correction increasing the defect score in some patients. Minor degrees of mal-registration (even of 1 pixel) between emission and transmission images increased the likelihood of creating a defect. ConclusionAttenuation correction using Hawkeye is likely to improve diagnostic accuracy in men, but is less likely to be useful in women.

Evaluation of 99mTc(CO)5I as a potential lung perfusion agent

INTRODUCTION The use of (99m)Tc-macroggregated albumin for lung perfusion imaging is well established in nuclear medicine. However, there have been safety concerns over the use of blood-derived products because of potential contamination by infective agents, for example, Variant Creutzfeldt Jakob Disease. Preliminary work has indicated that Tc(CO)(5)I is primarily taken up in the lungs following intravenous administration. The aim of this study was to evaluate the biodistribution and pharmacokinetics of (99m)Tc(CO)(5)I and its potential as a lung perfusion agent. METHODS (99m)Tc(CO)(5)I was synthesized by carbonylation of (99m)TcO(4-) at 160 atm of CO at 170 degrees C in the presence of HI for 40 min. Radiochemical purity was determined by HPLC using (99)Tc(CO)(5)I as a reference. (99m)Tc(CO)(5)I was administered by ear-vein injection to three chinchilla rabbits, and dynamic images were acquired using a gamma camera (Siemens E-cam) over 20 min. Imaging studies were also performed with (99m)Tc-labeled macroaggregated albumin ((99m)Tc-MAA) and (99m)TcO(4-) for comparison. (99m)Tc(CO)(5)I was administered intravenously to Sprague-Dawley rats, and tissue distribution studies were obtained at 15 min and 1 h postinjection. Comparative studies were performed using (99m)Tc-MAA. RESULTS Radiochemical purity, assessed by HPLC, was 98%. The retention time was similar to that of (99)Tc(CO)(5)I. The dynamic images showed that 70% of (99m)Tc(CO)(5)I appeared promptly in the lungs and remained constant for at least 20 min. In contrast, (99m)TcO(4-) rapidly washed out of the lungs after administration. As expected (99m)Tc-MAA showed 90% lung accumulation. The percentage of injected dose per gram of organ +/-S.D. at 1 h for (99m)Tc(CO)(5)I was as follows: blood, 0.22+/-0.02; lung, 12.8+/-2.87; liver, 0.8+/-0.15; heart, 0.15+/-0.01; kidney, 0.47+/-0.08. The percentage of injected dose per organ +/-S.D. at 1 h was as follows: lung, 22.47+/-2.31; liver, 10.53+/-1.8; heart, 0.18+/-0.01; kidney, 1.2+/-0.17. Tissue distribution studies with (99m)Tc-MAA showed 100% lung uptake. CONCLUSION (99m)Tc(CO)(5)I was synthesized with a high radiochemical purity and showed a high accumulation in the lungs. Further work on the mechanism and optimization of lung uptake of (99m)Tc-pentacarbonyl complexes is warranted.

Thallium-201 myocardial imaging in patients with angina pectoris and anomalous aortic origin of the circumflex coronary artery

Anomalous aortic origin of the circumflex coronary artery is the commonest coronary artery anomaly. In this study, the significance of anomalous aortic origin of the circumflex coronary artery was investigated in seven patients with exertional chest pain using exercise thallium scintigraphy. Five patients with circumflex coronary arterial disease served as controls. Myocardial perfusion was normal in the five patients with a nonstenosed anomalous artery. In these patients, exercise heart rate and blood pressure response were normal. Two patients with a stenosed anomalous circumflex coronary artery and four of the five control patients had posterolateral myocardial perfusion defects. It is concluded that anomalous aortic origin of the circumflex coronary artery does not cause impairment of myocardial perfusion unless it is the site of significant coronary arterial stenosis.

Pitfalls and Limitations of Radionuclide Renal Imaging in Adults

To understand pitfalls and limitations in adult renography, it is necessary to understand firstly the physiology of the kidney, especially the magnitude and control of renal blood flow, glomerular filtration rate and tubular fluid flow rate, and secondly the pharmacokinetics and renal handling of the three most often used tracers, Tc-99m-mercaptoacetyltriglycine (MAG3), Tc-99m-diethylene triamine pentaacetic acid (DTPA) and Tc-99m-dimercaptosuccinic acid (DMSA). The kidneys may be imaged dynamically with Tc-99m-MAG3 or Tc-99m-DTPA, with or without diuretic challenge, or by static imaging with Tc-99m-DMSA. Protocols are different according to whether the kidney is native or transplanted. Quantitative analysis of dynamic data includes measurement of renal vascularity (important for the transplanted kidney), absolute tracer clearance rates, differential renal function (DRF) and response to diuretic challenge. Static image reveals functional renal parenchymal damage, both focal and global, is useful in the clinical management of obstructive uropathy, renal stone disease and hypertension (under angiotensin converting enzyme inhibition), and is the preferred technique for determining DRF. Diagnosis based on morphological appearances is important in transplant management. Even though nuclear medicine is now in the era of hybrid imaging, renal imaging remains an important subspecialty in nuclear medicine and requires a sound basing in applied physiology, the classical supporting discipline of nuclear medicine.

The problem of pulmonary embolism diagnosis in pregnancy

Pulmonary embolism (PE) is one of the major causes of maternal mortality. Despite the higher incidence of PE in pregnant women, accurate diagnosis is difficult, as the classic symptoms of PE can mimic some physiological changes in pregnancy. In addition, clinical scoring systems used in the non-pregnant population are not validated for use in pregnancy (Wells et al, 2001; Bourjeily et al, 2010). Consequently, PE diagnosis in pregnancy becomes a question of weighing the risks of the radiation dose from a ventilationperfusion (V/Q) scan or computerized tomography pulmonary angiogram (CTPA) against missing a potentially fatal condition. The current analysis was performed to identify the outcome of V/Q scans for suspected PE in a tertiary centre (Fig 1). 127 patients with suspected PE diagnosis were referred for V/Q over a 3-year period. Pregnant females who had an abnormal chest X-ray and received CTPA instead of V/Q were not included in this cohort. V/Q scans were reported as low probability in 89 (70%), intermediate probability in 37 (29%) and high probability in one. 18/37 patients with intermediate probability did not proceed to CTPA while one additional PE was identified from the remaining 19 CTPAs. 8/19 cases were found to have non-thrombotic pathology on the CTPA. In summary, of a total 127 V/Q, there were two confirmed cases of PE, one diagnosed after V/Q, and the other following subsequent CTPA. Of the 19 who underwent CTPA, four were treated with low molecular weight heparin (LMWH) (including the positive case) and the dose was decreased to prophylactic levels in another three. Of the 18 patients who did not have a CTPA, six continued to be treated with therapeutic dose LMWH. 14 (11%), 48 (38%) and 63 (49%) V/Qs were done in the first, second and third trimesters respectively. All except three patients had either chest pain or shortness of breath as the presenting symptom. The respective incidences of breathlessness were 3, 10 and 16, while those of chest pain were 8, 22 and 22. Both symptoms were reported in 3, 18 and 31 patients in the three respective trimesters. PE diagnosis was made in pregnant females with chest pain only at 15 and 32 weeks gestation. Bilateral lower limb Doppler ultrasound was performed in 48 (38%) of the patients with one positive result of superficial venous thrombosis (low probability V/Q). D-dimer (Diagnostica Stago, Parsippany, NJ, USA) was tested in 53 (41%) of the patients with only two normal results (reference range 0–250 ng/ml). No D-dimer was performed on the patients with PE. In this study only 2 (1 6%) of women scanned were diagnosed with PE, probably because physiological changes in pregnancy mimic symptoms of PE, making clinical diagnosis difficult. This is supported by the fact that more V/Q scans were performed in the second and third trimester, as symptoms of chest pain and dyspnoea increase with gestation. This contrasts with the actual PE incidence being similar in all three trimesters (Bourjeily et al, 2010). The small number of positive scans confirming PE may also be due to the perceived serious nature of the disease. PE has a mortality of 30% if untreated, but 8% with appropriate management, making it vital that the diagnosis is not missed in the non-pregnant population (Carson et al, 1992). On the other hand, V/Q or CTPA do result in radiation to both mother and fetus. With CTPA, imaging in pregnancy increases lifetime risk of breast cancer and while breast radiation dose from V/Q is smaller, the total dose of fetal radiation is higher (Mathews, 2006; Mclintock et al, 2012). These risks, although notable, are substantially less than those related to an undiagnosed PE. A total of 18 (14%) women had an intermediate V/Q result but did not have follow-up CTPA. Patient preference, from unwillingness for the mother and/or fetus to be exposed to any further radiation, or physicians’ choice, where clinical suspicion is not high enough to warrant therapy or low enough for further investigations, are likely possibilities. Implications of this study are that the true number of PE may be higher, especially because six patients continued to receive treatment-dose LMWH. Although LMWH treatment is generally safe, it does carry 0 8% risk of minor side effects and risk of antepartum and postpartum haemorrhage. Royal College of Obstetric Gynaecologists guidance mandates Doppler ultrasound scan of both lower limbs, as the diagnosis of a deep vein thrombosis (DVT) negates the need for any other investigations (Greer & Thomson, 2010). Despite this, Doppler scans were performed in only 48 (40%) patients. Given that all were negative, the usefulness of this procedure is questionable, especially in individuals with no symptoms. In addition, Dopplers are unable to detect the presence of pelvic DVT, the commonest DVT site in pregnancy. D-dimer was not assessed in 74 (58%) patients in this cohort. When performed, all except two cases had D-dimer above our normal range of 0–250 ng/ml. D-dimer cut-off of ≤500 ng/ml in conjunction with low clinical suspicion can rule out PE without any further investigations in non-pregnant patients (Greer & Thomson, 2010). In this cohort 23/53 correspondence

Thoracic scintigraphy in aluminosis: lymph node uptake on bone scan.

Unusual appearances on a bone scan are demonstrated in a 60-year-old retired man who presented with several months’ history of generalized weakness, fatigue, backache, and weight loss. He had worked as a welder for 30 years. Medical history included rheumatoid arthritis and type 2 diabetes mellitus. On clinical examination, he was mildly breathless; however, the rest of the systemic examination was unremarkable. Laboratory investigations revealed mildly elevated serum ferritin and liver transaminases. Computed tomography showed widespread emphysema, apical pulmonary fibrosis, and mediastinal lymphadenopathy. In view of the persistent backache, and computed tomography findings of adenopathy, a bone scan was performed to rule out underlying bony metastatic disease. Bone scan revealed multiple focal areas of uptake within the joints consistent with rheumatoid arthritis. Focal areas of uptake on the bone scan were also seen in the mid thorax anterior to the spine. This was subsequently confirmed to be within the mediastinal nodes on localization by single slice SPECT (single photon emission computed tomography)/Hawkeye GE Millennium VG. Mediastinoscopy and biopsy revealed aluminum particles in the mediastinal lymph nodes.

Contamination levels and doses to staff arising from the use of Technegas

The aim of this work was to assess the levels of airborne activity and contamination arising from Technegas ventilation scintigraphy and to estimate doses to staff. The maximum air concentration was below the 99Tcm-derived air concentration limit and considerably lower than reported levels for conventional radioaerosols. The level of contamination on staff gloves and aprons exceeded the body surface contamination limit in 63 and 9% of cases, respectively. Levels of contamination and air concentration were generally higher if the patient had difficulty with the administration procedure. Room surface contamination was very low. In 24% of cases activity was detectable on staff (either in the hair or nose) using gamma camera imaging. Annual skin doses from these sources are calculated to be below the limit for deterministic effects. Whole body effective doses are calculated to be similar to those received by staff performing other nuclear medicine studies. However, care should be exercised to keep exposure from both airborne and fixed sources to a minimum and a regular review of contamination levels is recommended. We recommend the wearing of gloves for all Technegas administrations and disposable hats and masks may be considered in certain cases.

How to Do a Transplant Renogram

The transplant renogram is a variation of the standard renogram that is optimized for the transplant kidney.

How to Do a Renogram

The renogram is a dynamic nuclear medicine study used to investigate kidney perfusion, function, and elimination of tracer.

How to Do a Diuresis Renogram

The diuresis renogram is just a variant of the standard renogram in which the urine flow rate is increased by administration of a diuretic.