A Survey of Thyroid Gland Scintigraphy

MATERIALS AND METHODS

A 10-question survey was designed to obtain information on thyroid imaging procedures. The questions were designed to cover the procedure recommendations of the SNM guidelines. The specific survey questions are listed in the Appendix.

The survey was sent to 350 hospitals with nuclear medicine departments, throughout the Northeast. The hospitals were randomly selected from the American Hospital Directory (www.ahd.com). The hospitals were located in 11 states, including New York, Pennsylvania, Michigan, Ohio, Connecticut, Vermont, Massachusetts, New Jersey, Virginia, North Carolina, and Maryland.

RESULTS

One hundred sixty-five surveys (47%) were returned from hospitals in 10 different states whose number of beds ranged from 35 to 501, with an average of approximately 200. The survey results are listed in Table 2.

DISCUSSION

Twenty-eight percent of the survey respondents use ^99mTc-pertechnetate exclusively for thyroid imaging. The SNM guidelines list the advantages and disadvantages of ^99mTc-pertechnetate and ¹²³I-iodide for thyroid imaging (Table 3) (2). In addition to those items (Table 3), many publications have reported discordant results for thyroid nodules when imaged with these 2 different agents (8–11). Cold thyroid nodules seen on a ¹²³I scan sometimes appear to accumulate ^99mTc-pertechnetate. A cold nodule could be a thyroid carcinoma. Therefore, some thyroid cancers might be missed if thyroid imaging is done exclusively with ^99mTc-pertechnetate. Some publications recommend that if a ^99mTc pertechnetate thyroid scan shows warm or hot palpable nodules and the clinical indication is to rule out thyroid cancer, the scan should be repeated with ¹²³I (11).

Although the SNM guidelines for thyroid imaging do not recommend that patients fast before receiving the radiopharmaceutical, 41% of the respondents ask the patient to fast before receiving the ¹²³I capsule. Fasting would have no effect on the absorption of ^99mTc-pertechnetate since it is administered intravenously. However, the oral route of administration may cause ¹²³I absorption to vary from patient to patient. Pharmacokinetically, drugs that are administered orally are dependent on several factors for absorption. They include stomach contents, pH of stomach, and gastrointestinal motility. All 3 are patient-specific and could change if the stomach contains food or medications that affect one of the above factors (12). Therefore, the 41% of the respondents that recommend fasting to patients may be trying to minimize these variables to ensure sufficient uptake of the radiopharmaceutical.

Most respondents take both anterior and oblique views. Markers on the images help to identify anatomic location. The SNM guidelines recommend that duplicate views be taken with and without markers. This recommendation ensures that markers, whether radioactive or nonradioactive, do not obstruct the view of any part of the thyroid. Some clinics use radioactive markers such as ⁵⁷Co, and some clinics use nonradioactive markers. The recommended number of counts should be collected from the thyroid, not the thyroid plus markers. A substantial number of clinics, 22.8%, reported obtaining only views without markers. A smaller number of clinics (8%) reported that only 1 anterior view is taken and that it is done with markers.

A major variable affecting image resolution is the number of counts acquired. Of the ¹²³I users that responded to question 7, 20% (11/54) acquire less than the minimum recommended 50,000 counts. The recommended acquisition time for ¹²³I imaging is a minimum of 10 min. Again, a significant number of ¹²³I users (29/90, or 32%) reported using an acquisition time of less than 10 min.

The size of the thyroid gland is often a factor used in the determination of a therapy dose for hyperthyroidism (3,4). Only 43.6% of the survey respondents reported a method to size the thyroid gland. We did not find this surprising as ultrasound can also be used to determine the size of thyroid lobes and nodules (13).

A large number of respondents (25.5%) use a parallel-hole collimator exclusively for imaging the thyroid. The exact reason was not identified but may be the cost of a pinhole collimator, the time required to change the collimator, or the lack of availability of a pinhole collimator for purchase with some camera models. During the data collection of this study, we discovered that a camera manufacturer had recommended to one clinic that a parallel-hole collimator be used for thyroid imaging.

CONCLUSION

The procedure used to obtain a thyroid scan varies from site to site. There is much deviation from the recommendations of the SNM guidelines. The greatest deviation from the guidelines occurs in the choice of collimation, the number of counts or amount of time used to acquire the images, and the lack of neck palpation for correlation with the scan.

The number of respondents exclusively using a parallel-hole collimator was surprising. If manufacturers are recommending the parallel-hole collimator for thyroid imaging, this finding warrants further investigation. Have equipment improvements over the years eliminated the need for pinhole images of the thyroid gland? This is the question we are currently investigating.

Continuing education programs offered by professional organizations and societies tend to focus on newer procedures or technology. For commonly performed studies such as thyroid imaging, perhaps there is a need for regular continuing education that may reduce the amount of procedure variability. Our survey did not ask if the nuclear medicine clinic was accredited by the Intersocietal Commission for the Accreditation of Nuclear Medicine Laboratories or by the American College of Radiology. We wondered whether there would be as much variability in the way these studies are performed if the responding clinics were accredited. Accreditation serves to standardize procedures and reporting for optimal patient care.

APPENDIX