Lalitha Ramanna

False-positive iodine-131 body scan caused by a large renal cyst.

Focal I-131 accumulation is generally a reliable indicator of functioning thyroid tissue or a differentiated thyroid cancer metastasis. Normal accumulation of activity may be seen in areas such as the intestinal tract, liver, and salivary glands. This report describes a patient with significant accumulation of I-131 in the right upper quadrant of the abdomen. The abnormality, first thought to represent metastastic thyroid carcinoma, was subsequently proven to be accumulation within a large renal cyst.

Correlation of thyroglobulin measurements and radioiodine scans in the follow-up of patients with differentiated thyroid cancer

Correlation of radioiodine (131I) scans and serum thyroglobulin (Tg) concentrations were performed in the follow‐up of 85 differentiated thyroid cancer patients who had undergone total thyroidectomy. Tg results were also compared with the control group of 33 thyroidectomized patients with no evidence of thyroid carcinoma and normal values for Tg established. Excellent correlation between Tg and scans was noted in patients with scan evidence of metastasis distant from the neck. Poor correlation was present in patients with scan evidence of local neck metastasis only, thyroid bed activity, and those with mediastinal activity. In addition, in 8% of the patients, the Tg assay could not be performed because of interfering antibodies. The conclusion is that elevated Tg concentration is a good indicator of metastasis outside of the neck as detected by 131I scans. Caution should be used when Tg alone is used in evaluating local neck metastasis demonstrated on scans. The significance of mediastinal activity warrants further investigation.

Evaluation of low-dose radioiodine ablation therapy in postsurgical thyroid cancer patients.

Nineteen patients with differentiated thyroid carcinoma were given low dose (30 mCi) radioiodine therapy for the ablation of residual thyroid tissue following total thyroidectomy. Using 5- to 10-mCi diagnostic I-131 scans, ablation was achieved in two of 19 patients following the first low dose and three of 12 patients following the second low-dose therapy. The ablation response was 53% (ten of 19) following one large dose (100 mCi) in another concurrent group of 19 patients. The ablation response following the first low dose when compared with the first high-dose therapy was significantly lower (P=0.015). The combined ablation response following first and second low doses (five of 14) when compared to a single large dose was not significantly different (P=0.534). The use of low-dose-l-131 therapy, although not as effective as large dose therapy, may be warranted in patients resistant to entering the hospital for therapy. However, ablation as defined by a five- to ten-mCi I-131 scan can be expected to occur in only one third of the patients after two attempts at ablation, while a single 100-mCi regimen can be successful in achieving ablation in over one half of the patients after the first attempt.

Treatment Rationale in Thyroid Carcinoma Effect of Scan Dose

The authors have previously shown that the definition of ablation of thyroid tissue in patients treated with thyroidectomy and radioiodine (l-131) for thyroid carcinoma depends upon the dose of l-131 used to scan the patient. The therapeutic response to l-131 therapy was evaluated in a group of ten differentiated thyroid cancer patients who had a negative 2-mCi (-2 mCi) diagnostic study, but had a positive 10-mCi (+10 mCi) diagnostic study (group 1) during their follow-up evaluation. These results were compared to another group of ten differentiated thyroid cancer patients who received l-131 ablation therapy based on a positive 2-mCi (+2 mCi) l-131 scan (group 2). Six patients in group 1 and eight in group 2 had improvement or ablation of residual tissue based on the 10-mCi scan following therapy. The difference in response between the two groups was not statistically significant (P=0.63) by two-tailed Fishers exact test, indicating that even patients with -2-mCi, but +10-mCi scans may respond to l-131 therapy. Whether the large dose therapy makes any impact on the clinical outcome has not been answered by this study.

False-positive lung imaging: inadvertent injection into a pulmonary artery catheter.

A case of a ventilation-perfusion mismatch seen postoperatively in a patient with chest pain is reported. There was absence of perfusion to the right lung, with relatively normal ventilation. The study was initially interpreted as indicating a high probability of pulmonary embolus. It was then discovered that the injection had been inadvertently made into a Swan-Ganz catheter, with its tip in the left main pulmonary artery. The mismatch was therefore iatrogenic and not related to pulmonary embolus. The false-positive lung imaging which resulted has not been previously reported in the literature.

Regional function in a kidney with duplex collecting system.

A regional function evaluation using isotopes was useful prior to surgery in a patient with a duplex renal-collecting system.

A METHOD FOR DETERMINING CHANGES IN V-Q RATIOS DUE TO INTERVENTION: THE EFFECT OF EXERCISE ON RESTING LEVELS

Changes in regional V–Q ratios in response to various interventions have been evaluated using complex techniques. The purpose of this study was to develop a new and practical technique for accurately assessing changes in relative perfusion and ventilation in response to an intervention. For this purpose we have chosen to evaluate this method to access changes in V–Q values at rest and exercise. 18 male subjects underwent resting ventilation images using krypton-81 followed by perfusion images using 300 uCi of Tc-99m-MAA. All images contained 500,000 counts and were obtained in the posterior position. Using a cycle argometer, 80% of the maximal predicted heart rate was obtained and maintained for a 5− minute period. The subjects again breathed krypton, and an exercise ventilation image was obtained. This was immediately followed by a 3 mCi Tc-99m-MAA perfusion study. All information was acquired on computer using a 64x64 matrix. Positioning was kept constant by alignment of cobalt sources attached to the subjects back. The lung was trisected, allowing for regional analysis of V–Q ratios. This method was capable of demonstrating a significant increase in perfusion of upper lung zones in response to exercise. The resting perfusion to the right lung was significantly greater than the left, and during exercise there was a major trend to equalize perfusion between the two lungs. Ventilation increased over the right lung, resulting in a relatively higher V–Q ratio on the right than on the left. This method is simple to perform and analyze, and may have a role in determining the effects of therapeutic regimens in cardiovascular or pulmonary disease.