Fig. 40.1
It is important to examine the patient’s neck for any masses or signs of prior surgery before the patient is imaged. Also, when imaging, the patient’s chin should be up while the neck is extended as in this case
Several radiotracers or combinations of radiotracers and techniques, including subtraction imaging, have been utilized for this imaging procedure, but 99mTc-sestamibi is currently considered the international standard radiopharmaceutical as it is more accurate and less cumbersome than others. 99mTc-sestamibi localizes in both functioning parathyroid and thyroid tissue with the radiotracer washing out of normal thyroid tissue more rapidly than abnormal parathyroid tissue. SPECT-CT increases sensitivity and specificity, and aids in more precise anatomic localization of parathyroid adenomas [5]. For the sake of completeness, a short summary of alternative radiopharmaceuticals being used is discussed in a subsequent section of this chapter.
Indications
- (a)
Localization of a parathyroid adenoma(s) in patient with primary hyperparathyroidism or localization of any hyperfunctioning parathyroid tissue (hyperplasia). The clinical information of elevated calcium and parathyroid hormone can be very useful [5].
- (b)
Localization of any other type of hyperfunctioning parathyroid tissue (lower sensitivity in these cases).
Examination Time
About 3 h if both of early and delayed images are acquired.
About 45 min if only early images are obtained for presurgical purposes (per referring physician request).
Patient/Scan Preparation
- 1.
No specific patient preparation is required EXCEPT THAT PATIENT MUST BE ABLE TO LIE VERY STILL DURING IMAGING. SEDATION MAY BE NEEDED FOR PATIENTS UNABLE TO REMAIN STILL.
- 2.
Some have suggested discontinuing calcium channel blockers prior to the procedure.
- 3.
Documentation of elevated serum calcium and PTH levels, potential presence of concurrent thyroid disease, history of any prior thyroid or parathyroid surgery, prior administration of iodine-containing substances, and any other relevant imaging.
Radiopharmaceutical , Administered Activity, and Technique of Administration
Radiopharmaceutical: 99mTechnetium-sestamibi.
Administered activity: 20 mCi (740 MBq), range 10–35 mCi.
Route of administration: Intravenous.
(See Figs. 40.2, 40.3, and 40.4 for examples of a hot lab, dose label, and lead pig.)
Fig. 40.2
Example of a hot lab where the radiotracer is prepared
Fig. 40.3
Example of a label of a 99mTc-sestamibi dose (identifiers removed). Note that the dispensed dose, 27.08 mCi, is higher than the actual ordered or prescribed dose of 25.0 mCi. This discrepancy allows for interim decay of the radiotracer before the actual administration
Fig. 40.4
The radiotracer to be injected is carried in a lead “pig” in order to prevent radiation exposure to surrounding patients and technologists
Equipment and Energy Windows (See Figs. 40.5 and 40.6)
Fig. 40.5
Note that the patient is placed in the supine position with the gamma camera and CT aligned in order to scan from the level of the parotid gland to the mid-heart. This large field of view limits the possibility of missing ectopic parathyroid tissue
Fig. 40.6
Note the computer console to the right of the arrow. Parameters for the images are digitally entered into this console
Camera: Large field-of-view dual-headed gamma camera.
Collimator: Low-energy-high-resolution parallel hole.
Energy window: 20 % Centered at 140 keV.
Patient Positioning and Imaging Field
Patient position: Supine.
Imaging field: Base of brain to inferior border of heart.
Acquisition Protocols and Acquisition Parameters [6]
Wait for 15 min following radiopharmaceutical injection prior to imaging.
At 15 min: High-count images are obtained in the planar projection in three views: LAO, RAO, and anterior collimation can be achieved by using a high-resolution parallel-hole collimator (a pinhole collimator can be used). If SPECT or SPECT-CT is unavailable, pinhole collimation is preferred. It is imperative to obtain images of the neck, including the parotid glands and extending caudally to at least the mid-myocardium. This protocol is especially helpful in recurrent hyperparathyroidism or patients with residual disease as the adenoma(s) occur most often in ectopic anatomical locations in these settings [7].
Planar Static Images
Matrix: 128 × 128.
Zoom: Zero.
Acquire for 5 min in the ANT, R ANT OBLIQUE, and L ANT OBLIQUE projections.
SPECT-CT Images : (See Table 40.1 and 40.2) [7]
Table 40.1
Sample parameters for correlative CT
Parameters | CT |
|---|---|
Slice thickness | 5 mm |
Increment | 5 mm |
Number of scans | 1 |
Rotation time | 0.5 s |
Pitch | 0.9 |
Voltage | 140 ke V |
Current | 20 mAs |
Reconstruction matrix | 512 × 512 |
Number of reconstructed slices | 120 |
Starting angle*
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