Dennis, Jennifer Lucy
The use of single photon emission computed tomography in the investigation of parathyroid and thyroid disorders.
PhD thesis, University of Glasgow.
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Nuclear medicine is a functional imaging modality involving the administration of a radioactive material and the imaging of its distribution within the body. Planar nuclear medicine imaging has been used for many years in the evaluation of patients with disorders of the parathyroid and thyroid glands. Single photon emission computed tomography (SPECT) can also be carried out. This is a three-dimensional nuclear medicine imaging technique that gives both increased image contrast due to the separation of overlying structures and improved information on lesion localisation.
Currently, there is no definitive procedure for parathyroid imaging, which is primarily used for localisation of adenomas or hyperplastic glands in patients with hyperparathyroidism. This information can be used to assist during surgery to remove the overactive glands. Some centres use a single-isotope, dual-phase technique with 99mTc-Sestamibi, whilst others use a dual-isotope subtraction technique with either 99mTc-pertechnetate or 123I-iodide to outline the thyroid. Single-isotope SPECT is used in some institutions but there is little information on the use of dual-isotope subtraction SPECT.
Thyroid imaging with either 99mTc-pertechnetate or 123I-iodide is used to characterise thyroid disorders. The thyroid uptake can also be calculated using planar images, which can assist in clinical decision making for patients with hyper- or hypothyroidism. SPECT is not commonly used in thyroid imaging at present.
This study was carried out in the Department of Nuclear Medicine, Glasgow Royal Infirmary (GRI) and was split into two distinct sections, the first being an assessment of the utility of dual-isotope subtraction SPECT for localisation of parathyroid adenomas and the second being an evaluation of the use of SPECT imaging for calculating thyroid uptake. A custom designed and built phantom was used to assess the feasibility of parathyroid and thyroid SPECT imaging and to establish suitable acquisition parameters. The results from the phantom work demonstrated that the techniques were viable and so patient SPECT data collection was commenced.
A total of 32 patients with hyperparathyroidism underwent dual-isotope SPECT imaging in addition to routine planar imaging. The SPECT images were then reconstructed and a subtraction SPECT data set was produced. An observer study was then carried out with 5 experienced observers independently reviewing the images in 4 phases. In phase 1, only the dual-isotope subtraction planar images were available for review. Phase 2 was comprised of only dual-isotope subtraction SPECT images, whilst phase 3 involved review of single-isotope 99mTc-Sestamibi planar and SPECT images in the absence of 123I-iodide thyroid images. Finally, in phase 4, all of the acquired planar and SPECT images were available for review.
The patients’ case notes were interrogated to obtain information on the surgical and histological reports of excised glands. A total of 17 of the 32 patients had surgery and the results were compared to the findings from the observer study to determine which type of images provided the most useful clinical information. The results of any ultrasound imaging were also obtained to compare with the surgical findings.
The total number of lesions seen by the observers was higher when dual-isotope subtraction SPECT images were part of the review than when they were not, with totals in phases 1-4 of 89, 183, 89 and 155, respectively. The calculated sensitivities relative to the surgical gold standard for phases 1-4 were 49%, 77%, 45% & 64%, respectively, with ultrasound having a sensitivity of 72% for comparison. Dual-isotope subtraction SPECT therefore has a clear advantage over planar imaging for detection and localisation of parathyroid adenomas. The specificities for phases 1-4 were calculated as 61%, 31%, 29% & 27%, with the specificity for ultrasound being 33%. These specificities are, however, unreliable due to the fact that only 2 true negatives were recorded from surgery.
This study showed a clear improvement in the sensitivity of dual-isotope subtraction SPECT imaging over planar imaging for the detection and localisation of parathyroid adenomas, as well as more detailed localisation information being available from the 3D images. As a result, clinical practice in the department has been changed and all patients now routinely undergo dual-isotope subtraction SPECT imaging.
SPECT imaging with 99mTc-pertechnetate was carried out on 57 patients with thyroid disorders. The images were reconstructed with and without the inclusion of attenuation correction and the thyroid uptake was calculated by drawing a region of interest on each slice and summing the counts within each region. A standard acquisition was also carried out to allow accurate quantification to be performed. These uptake values were compared to those from planar imaging. Similar analysis was performed on images of a phantom to determine the accuracy of the patient uptake measurements.
The various uptake values calculated from the phantom images were all similar and were slightly lower than the “true” uptake value. However, there were significant differences demonstrated between the SPECT and planar uptake values from the patient images with the SPECT uptake tending to be higher. The reasons for this are not immediately clear but are most likely related to the difference in time between injection and imaging for the planar and SPECT acquisitions at 24.5 ± 8.0 minutes (mean ± 1SD) and 71.5 ± 17.5 minutes respectively.
Significant differences seen between the calculated uptake values from SPECT and planar images in the patient data sets were not evident in the phantom work, indicating that some physiological effect resulting in changing thyroid uptake over time was not taken into account. Further work could be undertaken to characterise this effect, but the method used to calculate the uptake from SPECT images is too cumbersome to be used routinely. Therefore, no change in clinical practice is anticipated for the calculation of thyroid uptake.
This study has therefore resulted in a change of clinical practice for parathyroid imaging at GRI, with the introduction of dual-isotope subtraction SPECT routinely. Thyroid imaging remains unchanged, however, with the thyroid uptake being calculated from planar images.
||SPECT, single photon emission computed tomography, parathyroid, dual-isotope subtraction, thyroid
||R Medicine > R Medicine (General)
||?? 40299000 ??
||Bolster, Dr. Alison A.
|Date of Award:
Mrs Jennifer L Dennis
||Copyright of this thesis is held by the author.
||07 Feb 2011
||10 Dec 2012 13:54
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