Usefulness of SPECT/CT in the Diagnosis of Intrathoracic Goiter versus Metastases From Cancer of the Breast

Hybrid SPECT/CT Imaging in the Management of Differentiated Thyroid Carcinoma

Differentiated thyroid cancer (DTC) has a good prognosis overall; however, lifelong follow-up is required for many cases. Radioiodine planar imaging with iodine-123 (I-123) or radioiodine-131 (I-131) remains the standard in the follow-up after initial surgery and ablation of residual thyroid tissue using I-131 therapy. Radioiodine imaging is also used in risk-stratifying and for staging of thyroid cancer, and in long-term follow-up. Unfortunately, the lack of anatomical detail on planar gamma camera imaging and superimposition of areas presenting with increased radioiodine uptake can make accurate diagnosis and localization of radioiodine-avid metastatic disease challenging, leading to false positive results and potentially to over-treatment of patients. Hybrid SPECT/CT allows precise anatomical localization and superior characterization of foci of increased tracer uptake when compared to planar imaging. This, in turn, allows the differentiation of pathological and physiological uptake, increasing the accuracy of image interpretation and ultimately improving the accuracy of DTC staging and subsequent patient management. In this review, we look at the unique and emerging role that SPECT/CT plays in the management of DTC, illustrated by examples from our own clinical practice.

Endocrine radionuclide scintigraphy with fusion single photon emission computed tomography/computed tomography

AIM: To review the benefits of single photon emission computed tomography (SPECT)/computed tomography (CT) hybrid imaging for diagnosis of various endocrine disorders.

METHODS: We performed MEDLINE and PubMed searches using the terms: “SPECT/CT”; “functional anatomic mapping”; “transmission emission tomography”; “parathyroid adenoma”; “thyroid cancer”; “neuroendocrine tumor”; “adrenal”; “pheochromocytoma”; “paraganglioma”; in order to identify relevant articles published in English during the years 2003 to 2015. Reference lists from the articles were reviewed to identify additional pertinent articles. Retrieved manuscripts (case reports, reviews, meta-analyses and abstracts) concerning the application of SPECT/CT to endocrine imaging were analyzed to provide a descriptive synthesis of the utility of this technology.

RESULTS: The emergence of hybrid SPECT/CT camera technology now allows simultaneous acquisition of combined multi-modality imaging, with seamless fusion of three-dimensional volume datasets. The usefulness of combining functional information to depict the bio-distribution of radiotracers that map cellular processes of the endocrine system and tumors of endocrine origin, with anatomy derived from CT, has improved the diagnostic capability of scintigraphy for a range of disorders of endocrine gland function. The literature describes benefits of SPECT/CT for ^99mTc-sestamibi parathyroid scintigraphy and ^99mTc-pertechnetate thyroid scintigraphy, ¹²³I- or ¹³¹I-radioiodine for staging of differentiated thyroid carcinoma, ¹¹¹In- and ^99mTc- labeled somatostatin receptor analogues for detection of neuroendocrine tumors, ¹³¹I-norcholesterol (NP-59) scans for assessment of adrenal cortical hyperfunction, and ¹²³I- or ¹³¹I-metaiodobenzylguanidine imaging for evaluation of pheochromocytoma and paraganglioma.

CONCLUSION: SPECT/CT exploits the synergism between the functional information from radiopharmaceutical imaging and anatomy from CT, translating to improved diagnostic accuracy and meaningful impact on patient care.

Endocrine scintigraphy with hybrid SPECT/CT

Nuclear medicine imaging of endocrine disorders takes advantage of unique cellular properties of endocrine organs and tissues that can be depicted by targeted radiopharmaceuticals. Detailed functional maps of biodistributions of radiopharmaceutical uptake can be displayed in three-dimensional tomographic formats, using single photon emission computed tomography (CT) that can now be directly combined with simultaneously acquired cross-sectional anatomic maps derived from CT. The integration of function depicted by scintigraphy and anatomy with CT has synergistically improved the efficacy of nuclear medicine imaging across a broad spectrum of clinical applications, which include some of the oldest imaging studies of endocrine dysfunction.

SPECT/CT localization of oral radioiodine activity: a retrospective study and in-vitro assessment

Purpose

We sought to further localize radioiodine activity in the mouth on post-thyroid cancer therapy imaging using single-photon emission computed tomography/computed tomography (SPECT/CT).

Materials and methods

We retrospectively reviewed all patients (58) who underwent thyroid cancer therapy with iodine-131 (¹³¹I) at our institution from August 2009 to March 2011 whose post-therapy radioiodine imaging included neck SPECT/CT. A small group (six) of diagnostic ¹²³I scans including SPECT/CT was also reviewed. Separately, we performed in-vitro ¹³¹I (sodium iodide) binding assays with amalgam and Argenco HP 77 (77% dental gold alloy) as proof of principle for these interactions.

Results

Of the 58 post-therapy patients, 45 (78%) had undergone metallic dental restorations, and of them 41 (91%) demonstrated oral ¹³¹I activity localizing preferentially to those restorations. It was observed that radioiodine also localized to other dental restorations and to orthodontic hardware. Gum-line activity in edentulous patients suggests radioiodine interaction with denture adhesive.

In vitro, dental amalgam and Argenco HP 77 bound ¹³¹I in a time-dependent manner over 1–16 days of exposure. Despite subsequent washings with normal saline, significant ¹³¹I activity (maximally 12% for amalgam and 68% for Argenco HP 77) was retained by these metals. Subsequent soaking in a saturated solution of potassium iodide partially displaced ¹³¹I from amalgam, with near-total displacement of ¹³¹I from Argenco HP 77.

Conclusion

SPECT/CT shows that radioiodine in the oral cavity localizes to metallic dental restorations. Furthermore, in-vitro studies demonstrate partially reversible binding of ¹³¹I to common dental metals.

SPECT/CT evaluation of unusual physiologic radioiodine biodistributions: pearls and pitfalls in image interpretation

Radioiodine imaging has a well-established role in depicting metastatic disease after thyroidectomy in patients with well-differentiated thyroid cancer. Uptake of radioiodine in thyroid metastases depends on expression of sodium-iodide symporter (NIS) by tumor tissues. However, because radioiodine may also accumulate in normal structures and tissues, it is important to distinguish physiologic radioiodine activity from metastatic disease. Furthermore, secretions that contain radioiodine may also simulate pathologic uptake. A spectrum of physiologic distributions, normal variants, and benign mimics of disease have been described in the literature; yet, even when armed with a comprehensive knowledge of these patterns, interpreting radiologists and nuclear physicians may still encounter diagnostic uncertainty. Single-photon emission computed tomography (SPECT) with integrated computed tomography (CT) is a novel technology that, when applied to diagnostic iodine 123 or iodine 131 ((131)I) radioiodine scintigraphy, may accurately localize and help distinguish benign mimics of disease, with the potential to alter the management plan. SPECT/CT is increasingly being used with radioiodine scintigraphy to evaluate patients with thyroid cancer and shows promise for improving imaging specificity and reducing false-positive results.

Radioiodine scintigraphy with SPECT/CT: an important diagnostic tool for thyroid cancer staging and risk stratification

Staging and risk stratification predicate the postoperative management of thyroid cancer patients, determining not only the need for (131)I therapy or alternative options (conservative management without ablation, surgical reintervention, or external-beam radiation therapy) but also the long-term follow-up strategy. This paper presents the progress made in the field of thyroid cancer imaging by application of SPECT/CT technology to radioiodine scintigraphy in both diagnostic and post-therapy settings and reviews the impact of fusion radioiodine imaging on staging, risk stratification, and clinical management of patients with thyroid cancer. In addition, this paper addresses the role of preablation radioiodine imaging and provides nuclear medicine physicians with the background knowledge required for integrating information from fusion imaging into the clinical and histopathologic risk stratification for developing an individualized treatment plan for patients with thyroid cancer.

SPECT/CT imaging: clinical utility of an emerging technology

Single-photon emission computed tomography (SPECT) has been a mainstay of nuclear medicine practice for several decades. More recently, combining the functional imaging available with SPECT and the anatomic imaging of computed tomography (CT) has gained more acceptance and proved useful in many clinical situations. Most vendors now offer integrated SPECT/CT systems that can perform both functions on one gantry and provide fused functional and anatomic data in a single imaging session. In addition to allowing anatomic localization of nuclear imaging findings, SPECT/CT also enables accurate and rapid attenuation correction of SPECT studies. These attributes have proved useful in many cardiac, general nuclear medicine, oncologic, and neurologic applications in which the SPECT results alone were inconclusive. Optimal clinical use of this rapidly emerging imaging modality requires an understanding of the fundamental principles of SPECT/CT, including quality control issues as well as potential pitfalls and limitations. The long-term clinical and economic effects of this technology have yet to be established.