Technical considerations in in vivo thyroid studies

Recognizing Pinhole Parallax Error for Accurate Localization of Thyroid and Parathyroid Disease

Parallax error is a pitfall of pinhole scintigraphy that causes mislocalization of the findings. It is important to notice this error on pinhole thyroid and parathyroid scintigraphy and obtain additional images with a parallel-hole collimator to accurately determine the upper and lower margins of large goiters and nodules and the location of ectopic thyroid tissue and parathyroid adenomas. In this teaching case report, we revisit pinhole parallax error, present pinhole and SPECT/CT images of a patient with a large, hyperactive thyroid nodule, and review the literature and potential solutions to this important problem.

Quantitative Measurement of the Thyroid Uptake Function of Mouse by Cerenkov Luminescence Imaging

Cerenkov luminescence imaging (CLI) has been an evolutional and alternative approach of nuclear imaging in basic research. This study aimed to measure the ¹³¹I thyroid uptake of mouse using CLI for assessment of thyroid function. Quantification of ¹³¹I thyroid uptake of mice in euthyroid, hypothyroid and hyperthyroid status was performed by CLI and γ-scintigraphy at 24 hours after injection of ¹³¹I. The ¹³¹I thyroid uptake was calculated using the equation: (thyroid counts − background counts)/(counts of injected dose of ¹³¹I) × 100%. Serum T4 concentration was determined to evaluate the thyroid function. The radioactivity of ¹³¹I was linearly correlated with the CL signals in both in vitro and in vivo measurements. CLI showed a significant decrease and increase of ¹³¹I thyroid uptake in the mice in hypo- and hyperfunctioning status, respectively, and highly correlated with that measured by γ-scintigraphy. However, the percent thyroid uptake measured by CLI were one-fifth of those measured by γ-scintigraphy due to insufficient tissue penetration of CL. These results indicate that CLI, in addition to nuclear imaging, is able to image and evaluate the ¹³¹I thyroid uptake function in mice in preclinical and research settings.

Comparison of pinhole and high-resolution parallel-hole imaging for nodular thyroid disease

INTRODUCTION AND OBJECTIVE

Pinhole has been the main standard collimator to be used for thyroid imaging. There has been a gradually increasing trend to replace pinhole with the use of high-resolution low-energy parallel-hole collimator with zoom in thyroid imaging. The objective of this study is to compare parallel-hole collimator acquisition of thyroid gland with that obtained by pinhole collimator to find the effect on the diagnostic information in nodular thyroid disease.

MATERIAL AND METHODS

A total of 29 patients, 24 women and 5 men, aged 18 to 70 years who were routinely referred for thyroid imaging for the assessment of nodular disease were studied. Each patient was injected with 185 MBq (5 mCi) of Tc-99m sodium pertechnetate intravenously. After 20 minutes, acquisition using pinhole followed by parallel-hole collimators was obtained. For pinhole acquisition, a 3-mm insert was used, and 3 images were obtained in the anterior and anterior oblique projections. For parallel-hole acquisition, anterior view was obtained for 250 K. The collimator was placed as close as possible to the patient. The image quality, number, and definition of nodules were evaluated by 2 independent, qualified nuclear medicine physicians. Differences were resolved by consensus.

RESULTS

There were 14 patients who had nodular patterns and 15 had no apparent nodules. There were 40 nodules of different sizes detected by pinhole imaging. Only 10 (25%) of these nodules were observed on parallel-hole images.

CONCLUSION

Pinhole imaging must be used for thyroid imaging particularly in patients suspected of having nodular disease.

A new method to measure thyroid uptake with a gamma camera without routine use of a standard source

PURPOSE

This study was designed to validate a reliable gamma camera-based method for measuring thyroid uptake. The method is based on a stable calibration procedure and does not require daily use of a standard source. In addition, the method is designed to overcome deadtime losses inherent in uptake probe measurements with iodine-123.

METHODS

A calibration procedure was designed using I-123 capsules in a neck phantom and tested using two gamma cameras. Patient thyroid uptake measurements made with the proposed gamma camera method were correlated with measurements obtained using the traditional uptake probe technique. Image quality was compared between the low-energy, parallel-hole collimator used in this study and the pinhole collimator usually used for thyroid imaging.

RESULTS

Capsule count rates measured using the gamma camera are linear with activity, and the calibration procedure is reproducible when tests are performed several months apart. Thyroid uptake measured with the gamma camera correlated closely (R2 > 0.9) with measurements made using the probe technique. Image quality with the low-energy parallel-hole collimator was comparable to that obtained with the pinhole collimator.

CONCLUSIONS

The proposed camera-based method for measuring thyroid uptake is accurate and reproducible. It can be performed readily in conjunction with the routine scan procedure. Adoption of this technique reduces equipment requirements in the nuclear medicine department.

Detection of metastatic thyroid carcinoma by 99mTc-pertechnetate in the presence of hyperfunctioning thyroid tissue

Neck metastases secondary to thyroid cancer are rarely visualized scintigraphically in the presence of a functioning thyroid gland. We present a patient with cervical lymph node metastases that take up 99mTc pertechnetate in the presence of hyperfunctioning thyroid tissue and discuss the pathophysiology of this phenomenon.

Management of thyroid nodules

This review describes the frequency of solitary thyroid nodules and their relationship to thyroid cancer. The importance of selecting patients appropriately for surgical excision is stressed. The factors predisposing to nodule formation and to a nodule being malignant are reviewed with emphasis that prior radiation exposure does not appear to increase the likelihood that a given nodule harbors a malignancy. In considering the laboratory evaluation of thyroid nodules, the limitations of isotope scans and ultrasonography are noted. Fine needle aspiration biopsy is described as revolutionizing the management of thyroid nodules and decreasing unnecessary operations. In the context of the natural history of differentiated thyroid cancer, the application of a decision analysis model to management options is described in some detail, and a cost-effective management regimen is recommended with fine needle aspiration biopsy as the initial procedure.

Improved quality and information in thyroid scintigraphy

We compared rectilinear scanning, analogous gamma-camera imaging and imaging using a gamma camera interfaced to a computer in order to determine which of these techniques is superior for thyroid scintigraphy. Forty patients with and without goitre and irregular activity distribution were imaged using each of the three techniques. The sets of three scintigrams per patient were rated by seven physicians. These ratings were statistically analysed using a new distribution-free test. Thyroid scintigraphy using a gamma camera interfaced to a computer turned out to be the best method, especially for detecting circumscribed areas of increased uptake. We conclude that this was due to a combination of the following factors: a computer matrix of 128 X 128 pixels in combination with an acquisition zoom of 1.5, the high count density of the scintigrams, computer-controlled documentation after data acquisition and the use of a continuous grey scale for documentation. The improved quality and information content of the scintigrams obtained using a gamma-camera/computer system could improve the diagnostic value of thyroid scintigraphy, especially when the scintigrams are also evaluated quantitatively.

Computed tomography findings in clinically normal and abnormal thyroid patients

Fifty normal volunteers had unenhanced thyroid computed tomography scans. A range of normal computed tomography densities and volumes was established for each age group. Pre- and postcontrast scans were done on 47 abnormal patients with hemorrhagic cysts, multinodular goiter, thyroiditis, papillary carcinoma, and benign adenomas. The computed tomography characteristics of each of the pathologic groups was noted for both the abnormal areas and the uninvolved part of the gland. Preliminary observations of the computed tomography characteristics of each abnormality are discussed.

The solitary thyroid nodule: diagnosis and management of malignant disease

While few solitary thyroid nodules are carcinomatous, it is essential to identify and preferentially select those that are for surgery. Clinical, biochemical, serologic, radiographic, scintigraphic, sonographic, biopsy, and even therapeutic evaluation may be necessary to choose those patients with the greatest probability of malignancy. The benefits and limitations of each diagnostic modality are discussed, and the importance of fine-needle aspiration is stressed. After the operative confirmation of malignancy, the prognosis in any given case depends on 1) the histologic type of the neoplasm, 2) its size and extent, 3) the presence of angioinvasiveness, 4) the tendency toward multicentricity of the lesion, 5) the age and sex of the patient, and 6) whether distant metastases are present. These factors influence the extent of surgery required for well-differentiated carcinomas. Meticulous dissection and preservation of the recurrent laryngeal nerves and the parathyroid glands along with their blood supply are important if total thyroidectomy for papillary carcinoma is to be employed with an acceptable operative morbidity to optimize survival. The value of the adjunctive use of thyroid hormone and radioactive iodine is also discussed. Finally, the clinical behaviors and treatments of undifferentiated carcinomas, sarcomas, lymphomas, and neoplasms metastatic to the thyroid gland are reviewed.