Usefulness of 99mTc-pertechnetate single-photon emission computed tomography in remnant mass estimation of postsurgical patients of differentiated thyroid cancer during internal dosimetry.

OBJECTIVE: No satisfactory methods exist for postsurgical remnant mass estimation required for dosimetric calculations in differentiated thyroid cancer patients undergoing I-131 remnant ablation. We estimated the remnant mass by Tc-99m pertechnetate single-photon emission computed tomography to calculate the radiation dose delivered. MATERIALS AND METHODS: Thyroid phantoms of known volumes (1.1-6 cm3) were fabricated, filled with different concentrations of Tc-99m pertechnetate activity, and single-photon emission computed tomography acquired on a dual head camera and processed with Hanning filter. Area of the organ on coronal slices was calculated at different thresholds and the sum was multiplied by slice thickness to get the volume. A threshold of 50% was found to distinguish the organ from the background activity and give the most accurate results. Remnant mass was calculated by this method in 50 patients of differentiated thyroid cancer after thyroid surgery. Effective half-life (EHL) of I-131 and 24 h radioactive iodine uptake (RAIU) were calculated by repeated neck count measurements for 4 days. After administering I-131 for therapy, 39 patients were followed up at 6 months and the effects of various parameters in achieving complete ablation were analyzed. RESULTS: Mean values of remnant mass, RAIU, and EHL were 6.6+/-4.3 g, 8.8+/-6.1%, and 4.5+/-0.9 days, respectively. Type of surgery, remnant mass, and RAIU were the most important predictors of complete ablation (P<0.05). Radiation-absorbed dose, EHL, and the administered activity had no significant effect on complete ablation. CONCLUSION: Remnant thyroid mass estimation by Tc-99m pertechnetate single-photon emission computed tomography is a simple technique and allows overcoming the dependence on structural imaging techniques or making empirical assumptions during dosimetry.

Comparison between dobutamine stress and combination of handgrip exercise with dobutamine stress in myocardial perfusion SPECT.

AIM: We compared the efficacy, side effects of combined handgrip exercise and dobutamine stress with dobutamine stress alone during myocardial perfusion imaging in patients unable to exercise, and in whom vasodilator stress was contraindicated. METHODS: We studied 126 consecutive patients (89 male, 37 female; mean age 63+/-8 years) referred for dobutamine stress myocardial perfusion SPECT. Patients were divided into Group A (n=63), who underwent only dobutamine stress and group B (n=63) who were subjected to combined handgrip exercise and dobutamine infusion. In group A patients, dobutamine was administered at a starting dose of 5 microg x kg(-1) x min(-1) increased to 10, 20 and 30 microg x kg(-1) x min(-1) to a maximum dose of 40 microg x kg(-1) x min(-1) at 3 min intervals until the target heart rate (THR, 85% of age predicted maximum heart rate) or other standard end point criteria were achieved. Group B patients were made to perform handgrip exercise 3 min prior to dobutamine infusion and continued throughout the administration of dobutamine. RESULTS: In group A, 11 (17.6%) patients failed to achieve target heart rate even with infusion of maximum dose of dobutamine compared to two (3.2%) in group B (P<0.01). The mean dose of dobutamine infused in group A was significantly higher than in group B (36.2 vs. 23.5 microg x kg(-1) x min(-1), P<0.01). Minor non-cardiac side effects like anxiety; flushing and nausea were observed in 25% of group A and in 11% of group B (P<0.05). Cardiac side effects and arrhythmias in group A and B were observed in 22% vs. 14.3% and 9.5% vs. 1.6% respectively (statistically insignificant). CONCLUSION: Combination of handgrip exercise with dobutamine reduces the total dose of dobutamine required to achieve target heart rate and likely to minimize the side effects associated with dobutamine.

Evaluation of dysfunction and malformations of the urinary tract in patients with meningomyelocele, by renal dynamic scintigraphy and direct radionuclide cystography. An Indian perspective.

Meningomyelocele (MMC) is the most common form of neural crest closure defect and may be associated with dysfunction and malformations of multiple organs including urinary tract. It affects as many as 2-4 in 1000 live births, however there are no epidemiological studies available from India. Anatomical and neurogenic abnormalities of the urinary tract are known to occur in these patients. Scanty literature is available regarding the utility of radionuclide procedures in the evaluation of urinary tract in patients of MMC. The aim of this study was to evaluate urinary tract dysfunction and malformations in patients operated of MMC by diuretic renal dynamic scintigraphy (RDS) and direct radionuclide cystography (DRCG). In this retrospective analysis, 140 operated patients for MMC, mean age: 4.46, range: 1-18 years; 83 male and 57 female, referred to our department for evaluation of the upper renal tract, were studied. Neurogenic bladder (NB) was associated in 69 patients. The diagnosis of NB was based on clinical features like incontinence, expressibility of urine bladder and on urodynamic studies. RDS was performed after the intravenous administration of 10.36 MBq/kg of technetium-99m diethylene triamine penta-acetate or 99mTc-L, L-ethylenedicysteine. All patients with hydronephrosis (HDN) or hydroureteronephrosis (HDUN) on RDS underwent DRCG using 11.1-18.5 MBq of 99mTc-sulphur colloid. Our results showed that: out of the 140 patients, 78 (56%) including 33 with NB, had normal renal scintigraphy. Six patients (4%) had congenital renal anomalies. Twenty patients (14%) revealed non-obstructive HDN and had no vesico-ureteric reflux (VUR). Thirty-six patients (26%) with bilateral HDUN also had NB of which 19 (53%) had VUR. Fourteen (74%) of these patients with VUR had impaired renal function. In discussion, patients with MMC may present with disordered innervation of the detrussor muscle and external sphincter, which adversely affects the bladder function and potentially threatens the upper urinary tract. Patients of MMC with or without NB can be evaluated with RDS for congenital anomalies and initial assessment of renal function. Patients with NB and particularly those with HDUN can be evaluated with DRCG for the presence of VUR to prevent renal scarring and subsequent impairment of renal function. Long-term surveillance of the urinary tract is important in the management of these patients and this can be accomplished with RDS and DRCG. In conclusion, in our patients with MMC, the tests of RDS, and DRCG could differentiate those with normal or our abnormal renal anatomy and function while the major group of patients had bilateral HDUN and NB, and/or VUR or impaired renal function.

Left ventricular ejection fraction and volumes on rest gated 201Tl perfusion SPECT: comparison with two-dimensional echocardiography.

BACKGROUND: Rest gated 201Tl images are considered to be of poor count statistics due to lower energy and low photon flux of 201Tl in addition to increased attenuation and low dose that can be administered. We compared the left ventricular ejection fraction (LVEF), end diastolic (EDV) and end systolic volume (ESV) obtained on 4 h gated rest 201Tl myocardial perfusion single photon emission computed tomography (SPECT) with those obtained by two-dimensional echocardiography (2-D ECHO) in patients with known or suspected coronary artery disease (CAD). METHODS: Eighty-two consecutive patients who underwent gated 201Tl stress-rest myocardial perfusion SPECT and 2-D ECHO were studied. The gated thallium images were processed with Siemens e-soft autocardiac processor and LVEF, EDV and ESV were evaluated using Emory Cardiac Toolbox. The same parameters were also assessed on the 2-D ECHO using the modified Simpson method for comparison. RESULTS: Out of 82 rest gated images, one study was excluded because of poor count statistics. In 81 (99%) patients there was good linear correlation with 2-D ECHO values and rest gated 201Tl SPECT images for EDV, ESV and LVEF. Pearson's correlation co-efficient (r value) for EDV, ESV and LVEF between the two methods was 0.78, 0.79 and 0.88, respectively. A Bland-Altman plot showed close agreement with LVEF but not for EDV and ESV. CONCLUSION: These results suggest that the 4 h rest gated 201Tl study gives a reliable value for the LVEF compared to 2-D ECHO and can be used in routine clinical practice.

Positron emission tomography: clinical applications in oncology. Part 1.

Positron emission tomography is a functional diagnostic imaging technique, which can accurately measure in vivo distribution of a radiopharmaceutical with high resolution. The ability of positron emission tomography to study various biologic processes opens up new possibilities for both research and day-to-day clinical use. Positron emission tomography has progressed rapidly from being a research technique in laboratories to a routine clinical imaging modality becoming part of armamentarium for the medical profession. The most widely used radiotracer in positron emission tomography is 18F-fluoro-2-deoxy-D-glucose (FDG), which is an analog of glucose. FDG uptake in cells is directly proportional to glucose metabolism of cells. Since glucose metabolism is increased many fold in malignant tumors, positron emission tomography has a high sensitivity and high negative predictive value. Positron emission tomography with FDG is now the standard of care in initial staging, monitoring the response to therapy and management of lung cancer, colorectal cancer, lymphoma, melanoma, esophageal cancer, head and neck cancer and breast cancer. The aim of this article is to review the clinical applications of positron emission tomography in oncology.