Hybrid SPECT–CT and PET–CT imaging of differentiated thyroid carcinoma

Abstract

Hybrid imaging modalities such as radioiodine single photon emission CT with integrated CT ((131)I SPECT-CT) and 2-(fluorine-18)-fluoro-2-deoxy-D-glucose positron emission tomography with integrated CT (FDG PET-CT) allow the rapid and efficient fusion of functional and anatomic images, and provide diagnostic information that may influence management decisions in patients with differentiated thyroid carcinoma (DTC). Diagnostic localisation and therapy of these tumours are dependent upon their capacity to concentrate radioiodine ((131)I) via uptake through the sodium-iodide symporter and retention within the tumour. The prognosis for most patients with DTC is favourable, although controversy exists regarding the role of post-operative (131)I therapy in patients at low-risk for disease. Accurate identification of functional thyroid tissue (benign or malignant) using diagnostic (131)I planar scintigraphy complemented by SPECT-CT imaging enables the completion of post-operative staging and patient risk stratification prior to (131)I therapy administration. In patients with non-iodine-avid tumours (negative (131)I scan but elevated thyroglobulin indicative of persistent or recurrent disease), FDG PET-CT is used to identify tumours with enhanced glucose metabolism and to localise the source of thyroglobulin production. The CT component of this hybrid technology provides anatomic localisation of activity and allows CT-based attenuation correction of PET images. Images from 15 patients illustrate the applications of (131)I SPECT-CT and FDG PET-CT.

Radioiodine Scintigraphy with SPECT/CT: An Important Diagnostic Tool for Thyroid Cancer Staging and Risk Stratification

“…SPECT/CT is an excellent diagnostic tool for rapid evaluation of suspected physiologic mimics and can accurately localize radioiodine distribution to salivary glands, dental fillings, retrosternal goiter, esophageal or airway secretions, hiatal hernias, bowel diverticula, breast, skin contamination, and benign uptake related to radioiodine retention in cysts, bronchiectasis, thymus, benign struma ovarii, or menstruating uterus (53)(54)(55)(56)(57)(58)(59). Several reports outline the usefulness of SPECT/CT for solving difficult diagnostic interpretations and revealing unusual metastatic lesions in the liver, kidney, central nervous system, erector spinae muscle, and rectus abdominis muscle (60)(61)(62)(63)(64).…”

SPET–CT in thyroid cancer: a systematic review

“…SPET-CT further characterized 21 out of 52 (40 %) foci of I-131 uptake, differentiating metastases from benign, physiological mimics of disease [28]. In a similar fashion, diagnostic I-131 SPET-CT performed before thyroid remnant ablation accurately characterized central neck and distant distributions of I-131 activity, correctly classifying equivocal planar imaging findings as benign or malignant [22,23]. The incremental value of SPET-CT over planar imaging was reported in 53 out of 130 (41 %) foci, with confident identification of thyroglossal duct and thyroid bed remnants [22,23].…”

“…In a similar fashion, diagnostic I-131 SPET-CT performed before thyroid remnant ablation accurately characterized central neck and distant distributions of I-131 activity, correctly classifying equivocal planar imaging findings as benign or malignant [22,23]. The incremental value of SPET-CT over planar imaging was reported in 53 out of 130 (41 %) foci, with confident identification of thyroglossal duct and thyroid bed remnants [22,23]. Others have confirmed that indeterminate neck lesions on planar scans, when restudied with SPET-CT, can be re-classified as thyroid remnants, lymph node metastases (Fig.…”

“…The identified I-131 and I-123 SPET-CT studies concerned patients prepared with either endogenous hypothyroidism or exogenous recombinant human TSH stimulation, and they used diagnostic imaging doses ranging from 37 to 430 MBq (1-11 mCi) [19][20][21][22][23][24] and post-therapy imaging doses ranging from 1.1 to 9.7? GBq (30-260?…”

“…Recommendation was for high-dose I-131 treatment and referral for external beam radiation therapy (color figure online) descent from the foramen cecum (near the tongue) to the thyroid bed. This tissue is not usually removed with total thyroidectomy and can create diagnostic uncertainty on post-surgical TSH-stimulated planar radioiodine scans [22,23]. This thyroglossal tract thyroid tissue was reported to be present in 39/83 (47 %) patients and could be accurately characterized on SPET-CT.…”