The clinical impact of a combined gamma camera/CT imaging system on somatostatin receptor imaging of neuroendocrine tumours

Two decades of SPECT/CT - the coming of age of a technology: An updated review of literature evidence

PURPOSE

Single-photon emission computed tomography (SPECT) combined with computed tomography (CT) was introduced as a hybrid SPECT/CT imaging modality two decades ago. The main advantage of SPECT/CT is the increased specificity achieved through a more precise localization and characterization of functional findings. The improved diagnostic accuracy is also associated with greater diagnostic confidence and better inter-specialty communication.

METHODS

This review presents a critical assessment of the relevant literature published so far on the role of SPECT/CT in a variety of clinical conditions. It also includes an update on the established evidence demonstrating both the advantages and limitations of this modality.

CONCLUSIONS

For the majority of applications, SPECT/CT should be a routine imaging technique, fully integrated into the clinical decision-making process, including oncology, endocrinology, orthopaedics, paediatrics, and cardiology. Large-scale prospective studies are lacking, however, on the use of SPECT/CT in certain clinical domains such as neurology and lung disorders. The review also presents data on the complementary role of SPECT/CT with other imaging modalities and a comparative analysis, where available.

Additional value of hybrid SPECT/CT systems in neuroendocrine tumors, adrenal tumors, pheochromocytomas and paragangliomas

The aim of this review was to evaluate the potential advantages of SPECT/CT hybrid imaging in the management of neuroendocrine tumors, adrenal tumors, pheochromocytomas and paragangliomas. From the collected data, the superiority of fused images was observed as providing both functional/molecular and morphological imaging compared to planar imaging. This provided an improvement in diagnostic imaging, with significant advantages as regards: (1) precise locating of the lesions; (2) an improvement in characterization of the findings, resulting higher specificity, improved sensitivity, and overall greater accuracy, (3) additional anatomical information derived from the CT component; (4) CT-based attenuation correction and potential for volumetric dosimetry calculations, and (5) improvement on the impact on patient management (e.g. in better defining treatment plans, in shortening surgical operating times). It can be concluded that SPECT/CT hybrid imaging provides the nuclear medicine physician with a powerful imaging modality in comparison to planar imaging, providing essential information about the location of lesions, and high quality homogeneous images.

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.

Case 227: Endobronchial Carcinoid Tumor with Incidental Metastatic Breast Cancer Detected with Somatostatin Receptor Scintigraphy ((111)In Pentreotide)

HISTORY

A 30-year-old woman with polycystic ovarian syndrome who was undergoing hormone replacement therapy presented with a 6-month history of a nonproductive cough and a 1-day history of hemoptysis (approximately 20 mL). Intravenous contrast material-enhanced (100 mL of Omnipaque 350; GE Healthcare, Princeton, NJ) computed tomographic (CT) pulmonary angiography was performed to evaluate for pulmonary embolism. On the basis of the CT pulmonary angiographic findings, chromogranin A and 5-hydroxyindoleacetic acid levels were measured and were 7 nmol/L (343 µg/L) (high) and 2.9 mg per 24 hours (15.167 µmol/d) (normal), respectively. This patient underwent bronchoscopy and biopsy. After these tests, she was referred for whole-body scintigraphy, which revealed an unexpected finding that was further investigated with fluorine 18 ((18)F) flurodeoxyglucose (FDG) positron emission tomography (PET) and CT.

A novel statistical analysis method to improve the detection of hepatic foci of (111)In-octreotide in SPECT/CT imaging

Background

Low uptake ratios, high noise, poor resolution, and low contrast all combine to make the detection of neuroendocrine liver tumours by ¹¹¹In-octreotide single photon emission tomography (SPECT) imaging a challenge. The aim of this study was to develop a segmentation analysis method that could improve the accuracy of hepatic neuroendocrine tumour detection.

Methods

Our novel segmentation was benchmarked by a retrospective analysis of patients categorized as either ¹¹¹In-octreotide positive (¹¹¹In-octreotide(+)) or ¹¹¹In-octreotide negative (¹¹¹In-octreotide(−)) for liver tumours. Following a 3-year follow-up period, involving multiple imaging modalities, we further segregated ¹¹¹In-octreotide-negative patients into two groups: one with no confirmed liver tumours (¹¹¹In-octreotide(−)/radtech(−)) and the other, now diagnosed with liver tumours (¹¹¹In-octreotide(−)/radtech(+)). We retrospectively applied our segmentation analysis to see if it could have detected these previously missed tumours using ¹¹¹In-octreotide. Our methodology subdivided the liver and determined normalized numbers of uptake foci (nNUF), at various threshold values, using a connected-component labelling algorithm. Plots of nNUF against the threshold index (ThI) were generated. ThI was defined as follows: ThI = (c_max − c_thr)/c_max, where c_max is the maximal threshold value for obtaining at least one, two voxel sized, uptake focus; c_thr is the voxel threshold value. The maximal divergence between the nNUF values for ¹¹¹In-octreotide(−)/radtech(−), and ¹¹¹In-octreotide(+) livers, was used as the optimal nNUF value for tumour detection. We also corrected for any influence of the mean activity concentration on ThI. The nNUF versus ThI method (nNUFTI) was then used to reanalyze the ¹¹¹In-octreotide(−)/radtech(−) and ¹¹¹In-octreotide(−)/radtech(+) groups.

Results

Of a total of 53 ¹¹¹In-octreotide(−) patients, 40 were categorized as ¹¹¹In-octreotide(−)/radtech(−) and 13 as ¹¹¹In-octreotide(−)/radtech(+) group. Optimal separation of the nNUF values for ¹¹¹In-octreotide(−)/radtech(−) and ¹¹¹In-octreotide(+) groups was defined at the nNUF value of 0.25, to the right of the bell shaped nNUFTI curve. ThIs at this nNUF value were dependent on the mean activity concentration and therefore normalized to generate nThI; a significant difference in nThI values was found between the ¹¹¹In-octreotide(−)/radtech(−) and the ¹¹¹In-octreotide(−)/radtech(+) groups (P < 0.01). As a result, four of the 13 ¹¹¹In-octreotide(−)/radtech(+) livers were redesigned as ¹¹¹In-octreotide(+).

Conclusions

The nNUFTI method has the potential to improve the diagnosis of liver tumours using ¹¹¹In-octreotide.

Contribution of ¹¹¹In-pentetreotide SPECT/CT imaging to conventional somatostatin receptor scintigraphy in the detection of neuroendocrine tumours

AIM

The aim of the study was to assess the contribution of 111In-pentetreotide single-photon emission computed tomography/computed tomography (SPECT/CT) imaging to conventional somatostatin receptor scintigraphy (SRS) in terms of lesion characterization and localization in the detection of neuroendocrine tumours (NETs).

MATERIALS AND METHODS

A total of 107 patients with suspected or confirmed NET underwent SRS and SPECT/CT after the injection of 148-222 MBq of 111In-pentetreotide. SRS and SPECT/CT images were interpreted independently. Each site of abnormal tracer uptake was recorded according to the anatomical localization, and as being consistent or not with NET. The findings were confirmed with pathological and/or clinical/imaging follow-up data.

RESULTS

A final diagnosis of NET was achieved in 49/107 patients (45.8%). No evidence of NET was found in the rest. SPECT/CT resulted in a significant reduction of indeterminate cases [14/107 (13.1%) vs. 1/107 (0.9%); P<0.001] and correctly reclassified one patient as negative for NET and another as positive for NET. SPECT/CT had 87.8% sensitivity and 96.6% specificity on a patient-based analysis, statistically higher than SRS (P<0.001). A total of 160 foci were detected (108 NETs and 52 physiological/benign tumours). SRS correctly classified 105/160 foci (65.6%) and remained inaccurate for 55 lesions. These 55 included 31 indeterminate lesions, 12 lesions detected only by SPECT/CT and 12 false-positive lesions. The number of foci correctly classified on the SPECT/CT images was 151/160 (94.4%), whereas two remained indeterminate and seven were false-positive findings.

CONCLUSION

SPECT/CT provides incremental diagnostic value over SRS, mainly because of a precise anatomical localization that helps discriminate between tumour lesions and physiological uptake. SPECT/CT may detect unsuspected lesions in a small proportion of patients.

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 and tumour imaging

Scintigraphic techniques are sensitive imaging modalities in the diagnosis and follow-up of cancer patients providing the functional and metabolic activity characteristics of the tumour. Hybrid SPECT/CT improves the diagnostic accuracy of these well-established imaging techniques by precise anatomical localization and characterization of morphological findings, differentiation between foci of physiological and pathological tracer uptake, resulting in a significant impact on patient management and more definitive interpretations. The use of SPECT/CT has been studied in a variety of applications in tumour imaging which are reviewed in this article. By combining functional and anatomical information in a single imaging session, SPECT/CT has become a one-stop cancer imaging modality.

Single photon emission computed tomography/computed tomography in the evaluation of neuroendocrine tumours: a review of the literature

The scintigraphic investigation of neuroendocrine tumours such as carcinoids has depended on standard techniques such as I-metaiodobenzylguanidine and In-pentetreotide imaging. More recently, the use of PET techniques such as Ga-DOTATATE has been advocated. An alternative improved modality is high-quality single photon emission computed tomography/computed tomography (SPECT/CT), which has the advantages of better sensitivity and specificity and has shown improved localization in up to 60% of cases. These advantages are especially true for pancreatic and lymph node lesions. Overall, SPECT/CT can result in a change in clinical management in 25% of patients. Although it is possible to combine SPECT and CT performed at different time points, there is better anatomical localization and improved reporter confidence when SPECT and CT are performed simultaneously.

Octreotide-mediated tumor cell uptake and intracellular pH-responsive drug delivery of the self-assembly supramolecular nanocarrier

In this study, DOX-loaded supramolecular nanocarrier (DLSC) was assembled by using two new amphiphilic polymers, octreotide-polyethylene glycol monostearate (OPMS) and N-octyl-N-succinyl O-carboxymethyl chitosan (OSCC). The characteristics of the DLSC were investigated. The results indicated that the significant pH-triggered release in vitro. The cellular uptake of DLSC was much higher than that of DOX-loaded OSCC micelles (DLOM) in the SMMC-7721 (somatostatin receptor (SSTR) over-expressed cell) cells, which suggested the SSTR-mediated properties. A considerable amount of drug entered the nucleus due to the pH-triggered deformation of the supramolecular structure and rapid release of drug in acidic endosomes of tumor cells. The killing efficacy was much higher than that of DLOM in the SMMC-7721. In S180 sarcoma-bearing KM mice, the biodistribution and therapeutic activity were studied. DLSC showed extended circulation time in plasma, decreasing drug concentrations in the heart and accumulating drug concentrations in the pancreas and tumor. In addition, minimized weight changes and cardiac toxicity, high suppression ratio of tumor growth and longer survival time were observed after intravenous injection of DLSC. The studies suggested that the supramolecular nanocarrier constructed of different designated polymers with multiple functions would be one of the most effective approaches for active targeting drug delivery.

Contemporary nuclear medicine imaging of neuroendocrine tumours

Neuroendocrine tumours (NETs) are rare, heterogeneous, and often hormonally active neoplasms. Nuclear medicine (NM) imaging using single photon- and positron-emitting radiopharmaceuticals allows sensitive and highly specific molecular imaging of NETs, complementary to anatomy-based techniques, such as computed tomography (CT) and magnetic resonance imaging (MRI). Somatostatin-receptor scintigraphy is a whole-body imaging technique widely used for diagnosis, staging and restaging of NETs. The increasing availability of hybrid single-photon emission CT (SPECT)/CT cameras now offers superior accuracy for localization and functional characterization of NETs compared to traditional planar and SPECT imaging. The potential role of positron-emission tomography (PET) tracers in the functional imaging of NETs is also being increasingly recognized. In addition to 2-[(18)F]-fluoro-2-deoxy-d-glucose (FDG), newer positron-emitting radiopharmaceuticals such as (18)F-dihydroxyphenylalanine (DOPA) and (68)Ga-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) peptides, show promise for the future. This article will summarize the role of current and emerging radiopharmaceuticals in NM imaging of this rare but important group of tumours.

Malignant pheochromocytomas and paragangliomas: a diagnostic challenge

INTRODUCTION

Malignant pheochromocytomas (PCCs) and paragangliomas (PGLs) are rare disorders arising from the adrenal gland, from the glomera along parasympathetic nerves or from paraganglia along the sympathetic trunk. According to the WHO classification, malignancy of PCCs and PGLs is defined by the presence of metastases at non-chromaffin sites distant from that of the primary tumor and not by local invasion. The overall prognosis of metastasized PCCs/PGLs is poor. Surgery offers currently the only change of cure. Preferably, the discrimination between malignant and benign PCCs/PGLs should be made preoperatively.

METHODS

This review summarizes our current knowledge on how benign and malignant tumors can be distinguished.

CONCLUSION

Due to the rarity of malignant PCCs/PGLs and the obvious difficulties in distinguishing benign and malignant PCCs/PGLs, any patient with a PCC/PGL should be treated in a specialized center where a multidisciplinary setting with specialized teams consisting of radiologists, endocrinologist, oncologists, pathologists and surgeons is available. This would also facilitate future studies to address the existing diagnostic and/or therapeutic obstacles.

Comparison of single time-point [111-In] pentetreotide SPECT/CT with dual time-point imaging of neuroendocrine tumors

PURPOSE

to determine whether single time-point single-photon emission computed tomography-computed tomography (SPECT/CT) somatostatin receptor imaging can replace traditional dual time-point planar and SPECT somatostatin receptor scintigraphy for evaluation of neuroendocrine tumors.

MATERIALS AND METHODS

twenty-four patients (9 males, 15 females; mean age: 56 years; range: 14-82 years) underwent [111-In] pentetreotide scintigraphy, with planar whole-body images acquired at 24 and 48 hours after injection and abdominal SPECT/CT at 24 hours postinjection. Two blinded readers independently interpreted each study, using single time-point (24 hours planar and SPECT/CT) and separately using dual time-point (24- and 48-hours planar, and 24-hour SPECT without CT) image information. Consensus interpretations were compared with surgical pathology, or clinical and radiologic follow-up for at least 12 months.

RESULTS

Interobserver agreement was excellent (κ = 0.86) for single time-point imaging, and good (κ = 0.56) with dual time-point imaging. After consensus review, single time-point imaging identified pathologic lesions in 11 of 12 subjects with diagnosis of NET at follow-up, and in 0 of 12 subjects without NET (sensitivity 92%; specificity 100%). Dual time-point imaging performed similarly, but missed an additional NET case (sensitivity 83%; specificity 100%). After review of SPECT/CT, the readers considered that additional 48 hours imaging was not necessary in the majority of cases, indicating high degree of confidence with the single time-point imaging.

CONCLUSION

[111-In] pentetreotide SPECT/CT imaging at 24 hours identifies pathologic disease sites and distinguishes physiologic activity equally well compared to traditional strategies using 2 imaging days. Routine use of SPECT/CT will allow single time-point imaging without loss of diagnostic accuracy, enhancing patient convenience, and clinical throughput.

Unknown primary tumors

An unknown primary tumor (UPT) is defined by the presence of a metastatic cancer without a known primary site of origin despite a standardized diagnostic workup. Clinically, UPTs show rapid progression and early dissemination, with signs and symptoms related to the metastatic site. The molecular bases of their biology remain largely unknown, with no evidence as to whether they represent a distinct biological entity. Immunohistochemistry remain the best diagnostic tool in term of cost-effectiveness, but the time-consuming "algorithmic process" it relies on has led to the application of new molecular techniques for the identification of the primary site of UPTs. For example, several microarray or miRNA classifications of UPTs have been used, with an accuracy in the prediction of the primary site as high as 90%. It should be noted that validating a prediction of tissue origin is challenging in these patients, since most of them will never have a primary site identified. Moreover, prospective studies to determine whether selection of treatment options based on such profiling methods actually improves patient outcome are still missing. In the last few years functional imaging (i.e. FDG-PET/CT) has gained a main role in the detection of the site of origin of UPTs and is currently recommended by the European Association of Nuclear Medicine. However, despite recent refinements in the diagnostic workup, the site of origin of UPT often remains elusive. As a consequence, treatment of patients with UPT is still empirical and inadequate.

Hybrid imaging (SPECT/CT and PET/CT)--improving the diagnostic accuracy of functional/metabolic and anatomic imaging

In-line combined systems, single-photon emission computed tomography (SPECT)/computed tomography (CT) and positron emission tomography (PET)/CT, allow an instant generation of fused images of scintigraphy and CT data. The accumulated clinical data on the use of these systems in various clinical scenarios indicate that this hybrid technology improves the diagnostic accuracy as compared to scintigraphy and CT alone and even to side-by-side interpretation of scintigraphy and CT, which were acquired separately. The improved diagnostic accuracy is reflected by improving image quality of SPECT and PET, detection of more clinically relevant lesions, better localization of disease and differentiation between physiologic and pathologic uptake, characterization of disease by its functional and morphologic appearance before and after therapy and accurate delineation of disease, optimizing biopsy and therapy planning.

[Radioguided surgery of intestinal carcinoid tumor relapse. Role of SPECT-CT]

We present a patient with clinical suspicion of intestinal carcinoid relapse confirmed by a somatostatin receptor scintigraphy. A very intense somatostatin avid abdominal lesion was located and radioguided surgery was proposed. Prior to the procedure, we performed a SPECT-CT that made it possible to detect and localize the lesion anatomically, thus facilitating the performance of the radioguided procedure. Furthermore, it modified the planning of the intervention with the adequate physical and human resources to prevent the possible surgical complications.

SPECT/CT stabilizes the interpretation of somatostatin receptor scintigraphy findings: a retrospective analysis of inter-rater agreement

OBJECTIVE

Correlating the anatomical information from CT with the functional information from SPECT improves diagnostic accuracy of somatostatin-receptor-scintigraphy (SRS) in patients with neuroendocrine tumors (NET). The aim of the present study was to investigate the impact of dual modality SPECT/CT on the inter-rater agreement in SRS.

METHODS

Twenty-five unselected patients with suspected or histologically proven NET in whom whole body planar imaging and low-dose SPECT/CT had been performed after injection of 200 MBq In-111-octreotide were included retrospectively. Images were interpreted independently by 2 nuclear medicine physicians, an experienced one and an inexperienced one. Both readers first re-evaluated the planar whole-body images alone, then added the SPECT images, and finally the CT-images. Lesions with pathologically increased tracer uptake were categorized according to the following 3-point score: equivocal, probably pathologic, and definitely pathologic. Cohen's linear-weighted kappa coefficient kappa was used to quantify inter-rater agreement.

RESULTS

A total number of 50 lesions were described in 23 of the 25 patients. The two readers showed only moderate agreement in the interpretation of the planar findings (kappa = 0.593). Agreement improved to substantial by adding SPECT (kappa = 0.736) and to very good by adding SPECT/CT (kappa = 0.860). SPECT/CT resulted in up-staging of 18% of the lesions and down-staging of 12% compared to planar + SPECT (experienced reader). In addition, SPECT/CT tended to reduce the frequency of indefinite scores (equivocal, probably pathologic), from 18% in planar + SPECT to 6% (p = 0.065). Change of lesion localization by SPECT/CT tended to contribute to the change of lesion score (p = 0.055).

CONCLUSION

The present results suggest that low-dose SPECT/CT stabilizes report quality in SRS by improving inter-rater agreement.

Attenuation correction of somatostatin receptor SPECT by integrated low-dose CT: is there an impact on sensitivity?

AIM

Somatostatin receptor scintigraphy (SRS) is an established imaging modality for neuroendocrine tumors (NET). Additional single photon emission computed tomography (SPECT-CT) not only permits image fusion but also attenuation correction (AC) of SPECT data. This study evaluated whether attenuation corrected SPECT-images (SPECT[AC]) are more sensitive than nonattenuation corrected SPECT-reconstructions (SPECT[NAC]) for the detection of NET lesions.

METHODS

The imaging data (planar In-111-octreotide scintigraphy and SPECT-CT) of 50 consecutive patients (28 male; 22 female; age, 34-80; mean, 65 years) with NET were included in this retrospective analysis. SPECT data were reconstructed with and without integrated CT-based AC and then analyzed by 2 experienced readers for the presence of pathologic uptake in a blinded consensus reading. Fused SPECT-CT, contemporary CT/MRI, and clinical as well as imaging follow-up served as a reference standard. All foci were rated in both the SPECT(NAC)- and SPECT(AC)-reconstructions for intensity and contrast using a 6-point-score ("0 = no uptake/no delineation from surrounding tissue" to "5 = very high uptake/very strong delineation from surrounding tissue"). The scores were analyzed in a 6 x 6 contingency table using the McNemar Bowker test.

RESULTS

A total of 222 pathologic foci were detected by SPECT(NAC) and 227 foci by SPECT(AC), respectively. In 67 of 227 foci (29.5%), focus intensity/contrast increased after AC, whereas only 5 foci showed a decrease (P < 0.001). Sensitivity increased by 2.2% (P = 0.025; 95% CI: 0.02%-4.1%) as 5 foci were detected only by SPECT(AC). However, as these 3 patients were already diagnosed with systemic disease, there was no influence on the therapeutic strategy chosen.

CONCLUSION

Attenuation correction of somatostatin receptor scintigraphy-SPECT significantly improves focus visualization and, albeit slightly, also significantly increases sensitivity.

Incremental value of 111-in pentetreotide SPECT/CT fusion imaging of neuroendocrine tumors

RATIONALE AND OBJECTIVES

Hybrid single photon-emission computed tomographic (SPECT) and computed tomographic (CT) imaging for the investigation of neuroendocrine tumors allows the fusion of functional and anatomic information in a rapid and efficient method. The aim of this study was to assess the incremental diagnostic value of (111)In pentetreotide SPECT/CT imaging compared with traditional planar and SPECT imaging with respect to lesion localization and characterization and reader confidence.

MATERIALS AND METHODS

Forty-nine patients (23 male, 26 female; mean age, 56.9 years; range, 14-88 years) who underwent (111)In pentetreotide planar, SPECT, and SPECT/CT imaging were eligible for this retrospective study, including patients with suspected or confirmed carcinoid tumors (n = 24), endocrine pancreatic tumors (n = 18), medullary thyroid cancer (n = 3), paragangliomas (n = 2), and multiple endocrine neoplasia type I (n = 2). Planar and SPECT images were reviewed by two blinded readers, followed by interpretation using additional SPECT/CT images in a subsequent session. A third reader provided consensus in cases with disagreements.

RESULTS

In 55 of 89 lesions (61.8%), (111)In pentetreotide SPECT/CT imaging improved lesion localization compared to planar and SPECT imaging; in 25 of 89 lesions (28.1%), SPECT/CT imaging changed lesion classification. In 20 of 49 patients (40.8%) for reader 1 and 14 of 49 patients (28.6%) for reader 2, (111)In pentetreotide SPECT/CT imaging provided incremental diagnostic value, which was considered likely to affect patient management in twelve of 20 and seven of 14 patients, respectively. Increased reader confidence was found in 32 of 49 patients (65.3%) for both readers with uniformly high confidence after SPECT/CT interpretation.

CONCLUSIONS

Hybrid (111)In pentetreotide SPECT/CT imaging provides incremental diagnostic value and greater reader confidence over planar and SPECT imaging. This is achieved though superior lesion localization, the identification of physiologic activity, and additional anatomic information derived from the nondiagnostic CT portion of the study.

Hybrid imaging (SPECT/CT and PET/CT): improving therapeutic decisions

The incremental diagnostic value of integrated positron emission tomography-computed tomography (PET/CT) or single-photon emission computed tomography (SPECT)/CT images compared with PET or SPECT alone, or PET or SPECT correlated with a CT obtained at a different time includes the following: (1) improvement in lesion detection on both CT and PET or SPECT images, (2) improvement in the localization of foci of uptake resulting in better differentiation of physiological from pathologic uptake, (3) precise localization of the malignant foci, for example, in the skeleton vs soft tissue or liver vs adjacent bowel or node (4) characterization of serendipitous lesions, and (5) confirmation of small, subtle, or unusual lesions. The use of these techniques can occur at the time of initial diagnosis, in assessing the early response of disease to treatment, at the conclusion of treatment, and in continuing follow-up of patients. PET/CT and SPECT/CT fusion images affect the clinical management in a significant proportion of patients with a wide range of diseases by (1) guiding further procedures, (2) excluding the need of further procedures, (3) changing both inter- and intramodality therapy, including soon after treatment has been initiated, and (4) by providing prognostic information. PET/CT fusion images have the potential to provide important information to guide the biopsy of a mass to active regions of the tumor and to provide better maps than CT alone to modulate field and dose of radiation therapy. It is expected that the role of PET/CT and SPECT/CT in changing management will continue to evolve in the future and that these tools will be fundamental components of the truly "personalized medicine" we are striving to deliver.

Somatostatin receptor tissue distribution in lung neuroendocrine tumours: a clinicopathologic and immunohistochemical study of 218 'clinically aggressive' cases

BACKGROUND

The management of pulmonary neuroendocrine tumours (NETs), with special reference to clinically aggressive carcinoids and large-cell neuroendocrine carcinomas (LCNECs), is poorly standardised and data about somatostatin receptor (SSTR) expression or therapeutic guidelines for somatostatin analogue administration are still debated.

MATERIALS AND METHODS

A series of 218 lung NETs [24 metastatic typical carcinoids (TCs), 73 atypical carcinoids (ACs), 60 LCNECs and 61 surgically resected small-cell lung carcinomas] were investigated for SSTR types 2A and 3 tissue distribution using immunohistochemistry, in correlation with clinicopathologic parameters, outcome, scintigraphy and treatment.

RESULTS

SSTRs were heterogeneously distributed with a significant progressive decrease from low- to high-grade forms. SSTR type 2A was strikingly overexpressed in metastatic TCs as compared with ACs and clinically benign TCs. SSTR tissue immunolocalization correlated with octreotide scintigraphy in 20 of 28 cases.

CONCLUSION

The immunohistochemical determination of SSTRs, with special reference to low-grade/intermediate-grade tumours, may assist the clinical approach with somatostatin analogue-based diagnostic and therapeutic procedures in clinically aggressive pulmonary NETs.

Inherited pancreatic endocrine tumor syndromes: advances in molecular pathogenesis, diagnosis, management, and controversies

Pancreatic endocrine tumors (PETs) can occur as part of 4 inherited disorders, including Multiple Endocrine Neoplasia type 1 (MEN1), von Hippel-Lindau disease (VHL), neurofibromatosis 1 (NF-1) (von Recklinghausen disease), and the tuberous sclerosis complex (TSC). The relative frequency with which patients who have these disorders develop PETs is MEN1>VHL>NF-1>TSC. Over the last few years, there have been major advances in the understanding of the genetics and molecular pathogenesis of these disorders as well in the localization and the medical and surgical treatment of PETs in such patients. The study of PETs in these disorders not only has provided insights into the possible pathogenesis of sporadic PETs but also has presented several unique management and treatment issues, some of which are applicable to patients with sporadic PETs. Therefore, the study of PETs in these uncommon disorders has provided valuable insights that, in many cases, are applicable to the general group of patients with sporadic PETs. In this article, these areas are reviewed briefly along with the current state of knowledge of the PETs in these disorders, and the controversies that exist in their management are summarized briefly and discussed.

Impact of 111In-DTPA-octreotide SPECT/CT fusion images in the management of neuroendocrine tumours

PURPOSE

Somatostatin receptor scintigraphy with [(111)In]-diethylene triamine pentaacetate acid (DTPA)-octreotide is an accurate method for detecting neuroendocrine tumours (NETs) but often does not provide clear anatomical localisation of lesions. The aim of this study was to assess the clinical usefulness of anatomical-functional image fusion.

MATERIALS AND METHODS

Fifty-four patients with known or suspected NET were included in the study. Planar and single-photon-emission computed tomography (SPECT) imaging was performed using a dual-head gamma camera equipped with an integrated X-ray transmission system, and the images were first interpreted alone by two nuclear medicine physicians and then compared with SPECT/CT fusion images together with a radiologist. The improvement provided by SPECT/CT in the interpretation of SPECT data alone and any modification in patient management were recorded.

RESULTS

Fusion images improved SPECT interpretation in 23 cases, providing precise anatomical localisation of increased tracer uptake in 20 cases and disease exclusion in sites of physiological uptake in 5. In 10 patients, SPECT/CT allowed definition of the functional significance of lesions detected by diagnostic CT. SPECT/CT data modified clinical management in 14 cases by changing the diagnostic approach in 8 and the therapeutic modality in 6.

CONCLUSIONS

Our study demonstrates that image fusion is clearly superior to SPECT alone, allowing precise localisation of lesions and reducing false-positive results.

Tumor receptor imaging

Tumor receptors play an important role in carcinogenesis and tumor growth and have been some of the earliest targets for tumor-specific therapy, for example, the estrogen receptor in breast cancer. Knowledge of receptor expression is key for therapy directed at tumor receptors and traditionally has been obtained by assay of biopsy material. Tumor receptor imaging offers complementary information that includes evaluation of the entire tumor burden and characterization of the heterogeneity of tumor receptor expression. The nature of the ligand-receptor interaction poses a challenge for imaging--notably, the requirement for a low molecular concentration of the imaging probe to avoid saturating the receptor and increasing the background because of nonspecific uptake. For this reason, much of the work to date in tumor receptor imaging has been done with radionuclide probes. In this overview of tumor receptor imaging, aspects of receptor biochemistry and biology that underlie tumor receptor imaging are reviewed, with the estrogen-estrogen receptor system in breast cancer as an illustrative example. Examples of progress in radionuclide receptor imaging for 3 receptor systems--steroid receptors, somatostatin receptors, and growth factor receptors-are highlighted, and recent investigations of receptor imaging with other molecular imaging modalities are reviewed.

Bronchopulmonary neuroendocrine tumors

Bronchopulmonary neuroendocrine tumors (BP-NETs) comprise approximately 20% of all lung cancers and represent a spectrum of tumors arising from neuroendocrine cells of the BP-epithelium. Although they share structural, morphological, immunohistochemical, and ultrastructural features, they are separated into 4 subgroups: typical carcinoid tumor (TC), atypical carcinoid tumor (AC), large-cell neuroendocrine carcinoma (LCNEC), and small-cell lung carcinoma (SCLC), which exhibit considerably different biological characteristics. The clinical presentation includes cough, hemoptysis, and obstructive pneumonia but varies depending on site, size, and growth pattern. Less than 5% of BP-NETs exhibit hormonally related symptoms such as carcinoid syndrome, Cushing, acromegaly, and SIADH. SCLC is the most common BP-NET, while LCNEC is rare, approximately 10% and < or =1%, respectively, of all lung cancers. Both SCLC and LCNEC progress rapidly, are aggressively metastatic, and exhibit a poor prognosis. The incidence of BP-carcinoids (TC and AC) in the US was 1.57 of 100,000 in 2003 (an unexplained and substantial increase over the last 30 years, approximately 6% per year). No curative treatment except for radical surgery (almost never feasible) exists. The slow-growing TC exhibit a fairly good prognosis ( approximately 88%, 5-year survival), whereas AC demonstrate a 5-year survival of approximately 50%, and the highly malignant LCNEC and SCLC5-year survival of 15% to 57% and <5%, respectively. This review provides a broad overview on BP-NETs and focuses on the evolution of the disease, general features, and current diagnostic and therapeutic options.

SPECT/CT

In view of the commercial success of integrated PET/CT scanners, there is an increasing interest in comparable SPECT/CT systems. SPECT in combination with CT enables a direct correlation of anatomic information and functional information, resulting in better localization and definition of scintigraphic findings. Besides anatomic referencing, the added value of CT coregistration is based on the attenuation correction capabilities of CT. The number of clinical studies is limited, but pilot studies have indicated a higher specificity and a significant reduction in indeterminate findings. The superiority of SPECT/CT over planar imaging or SPECT has been demonstrated in bone scintigraphy, somatostatin receptor scintigraphy, parathyroid scintigraphy, and adrenal gland scintigraphy. Also, rates of detection of sentinel nodes by biopsy can be increased with SPECT/CT. This review highlights recent technical developments in integrated SPECT/CT systems and summarizes the current literature on potential clinical uses and future directions for SPECT/CT in cardiac, neurologic, and oncologic applications.

Technological development and advances in single-photon emission computed tomography/computed tomography

Single-photon emission computed tomography/computed tomography (SPECT/CT) has emerged during the past decade as a means of correlating anatomical information from CT with functional information from SPECT. The integration of SPECT and CT in a single imaging device facilitates anatomical localization of the radiopharmaceutical to differentiate physiological uptake from that associated with disease and patient-specific attenuation correction to improve the visual quality and quantitative accuracy of the SPECT image. The first clinically available SPECT/CT systems performed emission-transmission imaging using a dual-headed SPECT camera and a low-power x-ray CT subsystem. Newer SPECT/CT systems are available with high-power CT subsystems suitable for detailed anatomical diagnosis, including CT coronary angiography and coronary calcification that can be correlated with myocardial perfusion measurements. The high-performance CT capabilities also offer the potential to improve compensation of partial volume errors for more accurate quantitation of radionuclide measurement of myocardial blood flow and other physiological processes and for radiation dosimetry for radionuclide therapy. In addition, new SPECT technologies are being developed that significantly improve the detection efficiency and spatial resolution for radionuclide imaging of small organs including the heart, brain, and breast, and therefore may provide new capabilities for SPECT/CT imaging in these important clinical applications.

The role of hybrid SPECT-CT in oncology: current and emerging clinical applications

Single photon emission computed tomography - computed tomography (SPECT-CT) is an emerging dual-modality imaging technique with many established and potential clinical applications in the field of oncology. To date, there has been a considerable emphasis on the benefits of integrated positron emission tomography - computed tomography (PET-CT) in oncology, but relatively little focus on the clinical utility of SPECT-CT. As with PET-CT, accurate co-registration of anatomical and functional data from a combined SPECT-CT camera often provides complementary diagnostic information. Both sensitivity (superior disease localization) and specificity (exclusion of false-positives due to physiological tracer uptake) are improved, and the functional significance of indeterminate lesions detected on cross-sectional imaging can be defined. This article will review the scope of hybrid SPECT-CT in oncology and illustrate both current and emerging clinical applications.

SPECTCT cerebral perfusion scintigraphy; is the low-dose CT component of diagnostic value?

AIM

To assess the potential diagnostic value of the low-dose computed tomography (CT) component of dual-examination single photon emission CT and CT (SPECTCT) cerebral perfusion studies.

METHOD AND MATERIALS

Two hundred and forty consecutive 99 mTc hexamethylpropylene amine oxime (HMPAO) SPECTCT studies were considered for inclusion. The images were acquired on a hybrid dual-head gamma camera/low-dose CT system. The CT component had a fixed tube current of 2.5 mA. The CT section thickness was 5mm and total acquisition time approximately 7.5 min. Studies in which no CT images were acquired, or those excessively degraded by movement artefact were excluded. The CT images of each of the remaining studies were retrospectively reviewed and categorized as normal or abnormal. Details of the abnormalities were recorded.

RESULTS

Fifteen of the 240 studies were excluded as no CT images were obtained. A further 14 were excluded as they were considered excessively degraded by movement artefact. A single abnormality was demonstrated on 48 (23%), and two abnormalities on four (2%) of the remaining 211 studies. The most common abnormal findings were low attenuation in the deep cortical white matter (n=22), infarcts (n=12), cerebral atrophy (n=7), dilated ventricles (n=5), basal ganglia calcification (n=4), and post-surgical change (n=3). Other findings included a chronic subdural haematoma, a meningioma, and a posterior fossa cyst. Previous cerebral imaging was available for comparison in 31% of cases. There was 85% concordance between previous imaging and the low-dose CT images.

CONCLUSION

Twenty-five percent of the low-dose CT images in this study demonstrated abnormalities. Therefore the CT component of cerebral perfusion SPECTCT investigations should be routinely reported in their own right.

Influence of attenuation correction by integrated low-dose CT on somatostatin receptor SPECT

AIM

Somatostatin receptor scintigraphy (SRS) is well-established in neuroendocrine tumour (NET) imaging. This study evaluated the impact of attenuation correction (AC) on SRS SPECT data in patients examined by SPECT-CT.

METHODS

Planar scintigraphy and SPECT-CT of 17 patients (10 men, seven women; age, 40-74 years; mean, 62 years) suffering from NET were included. For the visual assessment of AC, the intensity and contrast of foci classified as pathological were rated in both the non-attenuation corrected (NAC) and the attenuation corrected (AC) SPECT images using a 5-point score. The change in signal intensity after AC was semiquantified two-fold for each focus in both SPECT(AC) and SPECT(NAC): firstly by using tumour-to-background (TB) ratios (defined as T(max)/B(mean)) for the determination of a TB(AC)/TB(NAC) ratio. Secondly, by a T(max,AC)/T(max,NAC) ratio. Both ratios were correlated to the focus depth.

RESULTS

A total of 46 pathological foci were found. Focus contrast and intensity significantly increased in 14/46 foci (30%) after AC (mean, 3.7-4.0) in the visual analysis (P<0.001). While TB ratios increased only in 24/46 foci after AC and no correlation between the T(BAC)/T(BNAC) ratio and focus depth (r=0.027; P=0.856) was found, T(max) was higher after AC in all foci and the T(max,AC)/T(max,NAC) ratio showed the expected correlation to focus depth (r=0.650; P<0.01), indicating the superiority of the Tmax approach for the demonstration of the effects of attenuation correction on focal uptake.

CONCLUSION

Attenuation correction of SRS SPECT data by SPECT-CT results in visually more clearly contrasted foci. Moreover, as focus intensity increases, especially in the more centrally localised foci, CT-based AC has a potential to further improve the sensitivity of SRS SPECT.

Hybrid imaging is the future of molecular imaging

Correlative imaging has long been used in clinical practice and particularly for the interpretation of nuclear medicine studies wherein detailed anatomical information is often lacking. Previously, side-by-side comparison or software co-registration techniques were applied but suffered from technical limitations related to the differing geometries of the imaging equipment, differences in the positioning of patients and displacement of mobile structures between studies. The development of the first hybrid PET and CT device struck a chord with the medical imaging community that is still ringing loudly throughout the world. So successful has been the concept of PET-CT that none of the major medical imaging manufacturers now offers stand-alone PET scanners. Following close behind this success, SPECT-CT devices have recently been adopted by the nuclear medicine community, already compelled by the benefits of hybrid imaging through their experience with PET-CT. Recent reports of adaptation of PET detectors to operate within the strong magnetic field of MRI scanners have generated further enthusiasm. Prototype PET-MRI devices are now in development. The complementary anatomical, functional and molecular information provided by these techniques can now be presented in an intuitive and aesthetically-pleasing format. This has made end-users more comfortable with the results of functional imaging techniques than when the same information is presented independently. Despite the primacy of anatomical imaging for locoregional disease definition, the molecular characterisation available from PET and SPECT offers unique complementary information for cancer evaluation. A new era of cancer imaging, when hybrid imaging will be the primary diagnostic tool, is approaching.