Functional–Anatomical Image Fusion in Neuroendocrine Tumors

Paradigm shift in theranostics of neuroendocrine tumors: conceptual horizons of nanotechnology in nuclear medicine

We present a comprehensive review of Neuroendocrine Tumors (NET) and the current and developing imaging and therapeutic modalities for NET with emphasis on Nuclear Medicine modalities. Subsequently, nanotechnology and its emerging role in cancer management, especially NET, are discussed. The article is both educative and informative. The objective is to provide an insight into the developments made in nuclear medicine and nanotechnology towards management of NET, individually as well as combined together.

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.

Iodine-131MIBG SPECT/CT in neuroendocrine tumours: An institutional experience

Context:

Radiolabelled metaiodobenzylguanidine (MIBG) is commonly used for imaging of neuroendocrine tumors (NETs). The hybrid imaging with single photon emission computerized tomography/computerized tomography (SPECT/CT) co-registration can give that additional edge to this functional imaging modality.

Aims:

To study the additional value of ¹³¹I-MIBG SPECT/CT scintigraphy in evaluation of NETs.

Settings and Design:

We performed a retrospective study of the scintigraphic data of patients referred to our department for detection and follow-up of NETs from 2004 to 2008.

Materials and Methods:

Total number of studies were 370. Twenty-eight patients with equivocal findings on planar imaging had undergone additional SPECT/CT imaging. The contribution made by SPECT/CT imaging in these studies was analyzed.

Results:

In 27 of 28 cases, SPECT/CT provided vital additional information.

Conclusions:

We concluded that SPECT/CT co-registration helps in exclusion, identification, and localization of primary and metastatic NETs. It differentiates physiological from pathological tracer distribution. It helps increase the confidence in reporting, especially in equivocal findings on planar imaging.

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.

Nuclear medicine techniques for the imaging and treatment of neuroendocrine tumours

Nuclear medicine plays a pivotal role in the imaging and treatment of neuroendocrine tumours (NETs). Somatostatin receptor scintigraphy (SRS) with [(111)In-DTPA(0)]octreotide has proven its role in the diagnosis and staging of gastroenteropancreatic NETs (GEP-NETs). New techniques in somatostatin receptor imaging include the use of different radiolabelled somatostatin analogues with higher affinity and different affinity profiles to the somatostatin receptor subtypes. Most of these analogues can also be labelled with positron-emitting radionuclides that are being used in positron emission tomography imaging. The latter imaging modality, especially in the combination with computed tomography, is of interest because of encouraging results in terms of improved imaging quality and detection capabilities. Considerable advances have been made in the imaging of NETs, but to find the ideal imaging method with increased sensitivity and better topographic localisation of the primary and metastatic disease remains the ultimate goal of research. This review provides an overview of the currently used imaging modalities and ongoing developments in the imaging of NETs, with the emphasis on nuclear medicine and puts them in perspective of clinical practice. The advantage of SRS over other imaging modalities in GEP-NETs is that it can be used to select patients with sufficient uptake for treatment with radiolabelled somatostatin analogues. Peptide receptor radionuclide therapy (PRRT) is a promising new tool in the management of patients with inoperable or metastasised NETs as it can induce symptomatic improvement with all Indium-111, Yttrium-90 or Lutetium-177-labelled somatostatin analogues. The results that were obtained with [(90)Y-DOTA(0),Tyr(3)]octreotide and [(177)Lu-DOTA(0),Tyr(3)]octreotate are even more encouraging in terms of objective tumour responses with tumour regression and documented prolonged time to progression. In the largest group of patients receiving PRRT, treated with [(177)Lu-DOTA(0),Tyr(3)]octreotate, a survival benefit of several years compared with historical controls has been reported.

Automatic and manual image fusion of In-pentetreotide SPECT and diagnostic CT in neuroendocrine tumor imaging - An evaluation

In the clinical diagnosis of neuroendocrine tumors (NET), the results of examinations, such as high-resolution computed tomography (CT) and single photon computerized tomography (SPECT), have conventionally been interpreted separately. The aim of the present study was to evaluate Hermes Multimodality™ 5.0 H Image Fusion software-based automatic and manual image fusion of SPECT and CT for the localization of NET lesions. Out of 34 NET patients who were examined by means of somatostatin receptor scintigraphy (SRS) with 111In- pentetreotide along with SPECT, 22 patients had a CT examination of the abdomen, which was used in the fusion analysis. SPECT and CT data were fused using software with a registration algorithm based on normalized mutual information. The criteria for acceptable fusion were established at a maximum cranial or caudal dislocation of 25 mm between the images and at a reasonable consensus (in order of less than 1 cm) between outline of the reference organs. The automatic fusion was acceptable in 13 of the 22 examinations, whereas 9 fusions were not. However all the 22 examinations were acceptable at the manual fusion. The result of automatic fusion was better when the slice thickness of 5 mm was applied at CT examination, when the number of slices was below 100 in CT data and when both examinations included uptakes of pathological lesions. Retrospective manual image fusion of SPECT and CT is a relatively inexpensive but reliable method to be used in NET imaging. Automatic image fusion with specified software of SPECT and CT acts better when the number of CT slices is reduced to the SPECT volume and when corresponding pathological lesions appear at both SPECT and CT examinations.

Comparison of diagnostic value of I-123 MIBG and high-dose I-131 MIBG scintigraphy including incremental value of SPECT/CT over planar image in patients with malignant pheochromocytoma/paraganglioma and neuroblastoma

PURPOSE

to compare lesion detectability of I-123 MIBG scintigraphy with that of high-dose I-131 MIBG and to evaluate incremental benefit of SPECT/CT over planar image for the detection and localization of the lesions in patients with I-131 MIBG therapy for malignant pheochromocytoma/paraganglioma and neuroblastoma.

MATERIALS AND METHODS

we retrospectively investigated 16 patients with malignant pheochromocytoma/paraganglioma and neuroblastoma, who were referred for I-131 MIBG therapy. We investigated the lesion detectability in 10 pairs of I-123 and high-dose I-131 MIBG studies of the same patient, obtained within 2 weeks. In 31 studies of I-123 MIBG scintigraphy in 16 patients and 17 studies of high-dose I-131 MIBG scintigraphy in 12 patients, we compared planar and SPECT/CT images for the lesion detectability and localization.

RESULTS

the number of lesions detected by I-123 MIBG planer image and SPECT/CT and high-dose planer I-131 MIBG and SPECT/CT were 3.0 and 3.7, 7.3 and 7.7 per study, respectively. SPECT/CT images provided additional diagnostic information over planar images in 25 studies (81%) of 12 patients (75%) in I-123 MIBG scintigraphy and in 9 studies (53%) of 9 patients (75%) in high-dose I-131 MIBG scintigraphy.

CONCLUSION

post-therapy high-dose I-131 MIBG scintigraphy is superior to I-123 MIBG scintigraphy in lesion detectability even in comparison with I-123 MIBG SPECT/CT images and high-dose I-131 MIBG planar images in patients with malignant neuroendocrine tumors. SPECT/CT images are helpful for accurate identification of anatomic localization compared with planar images.

Incremental diagnostic value and impact on patient management of somatostatin receptor scintigraphy with indium-111-pentetreotide in gastroenteropancreatic neuroendocrine tumors

OBJECTIVE

To evaluate the efficacy of somatostatin analog scintigraphy with indium-111-pentetreotide and its overall impact on management in patients with gastroenteropancreatic neuroendocrine tumors (GEP-NET).

SUBJECTS AND METHODS

Twenty-two consecutive patients with a proven or clinically suspected GEP-NET with or without proven metastases were imaged at 24 and 48 h after injection of (111)In-pentetreotide. The scintigraphic findings were compared with results from conventional imaging methods. The final diagnosis was based on histopathological and surgical findings and complementary radiology.

RESULTS

Somatostatin receptor-positive lesions were found in 20 of the patients, whereas conventional methods were positive in 18 patients. Additionally, 13 new tumor sites were discovered by somatostatin receptor scintigraphy in 5 patients (liver: 6; chest: 2; bone: 1; abdomen: 4). The surgical therapeutic strategy was changed in 7 patients (32%).

CONCLUSIONS

Our data reinforced that scintigraphy with (111)In-pentetreotide represents the imaging modality of choice in the initial evaluation of GEP-NET. It is highly accurate and can identify clinically unsuspected lesions and optimize the overall staging. It also guides optimal therapy choice and most importantly identifies patients with inoperable or metastatic disease who might be candidates for high-dose targeted therapy.

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.

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.

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.

Infection scintigraphy: added value of single-photon emission computed tomography/computed tomography fusion compared with traditional analysis

PURPOSE

Positron emission tomography (PET)/computed tomography (CT) imaging is a powerful dual-modality integrating physiology and anatomy. Analogously, fusing separate single-photon emission computed tomography (SPECT) and CT images can overcome interpretive challenges in characterizing and localizing abnormalities. This study explores the value of SPECT/CT image fusion compared with traditional "side-by-side" SPECT-CT image review for infectious /inflammatory processes.

METHODS AND MATERIALS

We identified 17 abnormal infection/inflammation SPECT scans in 16 patients (11 indium 111 WBC and 6 gallium citrate Ga 67) with a contemporary CT scan. The SPECT and CT images were uploaded onto "side-by-side" workstations, one with fusion software. Two nuclear radiologists reviewed "side-by-side" SPECT and CT images and fused SPECT/CT images. They scored 2 parameters (anatomical localization and diagnostic confidence) using a 4-point scale (1 "not helpful" to 4 "very helpful"). Score differences more than 1 indicated "added value" and less than 0, "no added value".

RESULTS

Compared with "side-by-side" SPECT-CT, fused SPECT/CT images yielded "added value" for anatomical localization in 65%, diagnostic confidence in 71%, and altered interpretations in 47% of cases. Greater confidence was achieved in 75% of cases with altered interpretations and 55% of unaltered cases.

CONCLUSIONS

The SPECT/CT image fusion outperformed "side-by-side" SPECT/CT review for anatomical localization and diagnostic confidence of infectious/inflammatory abnormalities. Therefore, SPECT/CT fusion potentially influences clinical decisions and treatment options.

Endocrine neoplasm scintigraphy: added value of fusing SPECT/CT images compared with traditional side-by-side analysis

PURPOSE

Positron emission tomography (PET)/computed tomography (CT) imaging integrates physiology and anatomy, providing a powerful dual-modality approach. Analogously, fusing independently acquired single photon emission computed tomography (SPECT) and CT images can overcome interpretive challenges in characterizing and localizing abnormalities by either modality alone, potentially enhancing diagnostic confidence. This study explores the added value of SPECT/CT image fusion compared with traditional "side-by-side" SPECT/CT image review for a variety of endocrine neoplasms.

METHODS AND MATERIALS

We identified 11 abnormal endocrine neoplasm SPECT scans in 10 patients with contemporary relevant CT scans. These cases included: 4 I-131 (posttherapy thyroid cancer), 2 I-123 (pretherapy thyroid cancer), 2 In-111 OctreoScan (neuroendocrine neoplasm), one Tc-99m sestamibi (thyroid cancer), one Tc-99m tetrofosmin (parathyroid adenoma), and one I-123 MIBG (adrenergic neoplasm). SPECT and CT images were uploaded onto side-by-side workstations, one with fusion software. Two experienced nuclear radiologists first reviewed "side-by-side" SPECT/CT images followed by fused SPECT/CT images. They scored 2 parameters-anatomic localization and diagnostic confidence-using a 4-point scale (1 "not helpful" to 4 "very helpful"). Score differences > or =1 indicated "added value"; < or =0 indicated "lack of added value."

RESULTS

Compared with "side-by-side" SPECT/CT images, fused SPECT/CT images yielded "added value" for anatomic localization and diagnostic confidence in two thirds of cases. Fusion led to altered diagnoses in 4 of 11 examinations. Greater confidence was also achieved in 3 of 4 when the interpretation was changed and in 4 of 7 cases when it was not.

CONCLUSIONS

CT correlation can be helpful in interpreting endocrine neoplasm SPECT imaging. SPECT/CT image fusion outperformed "side-by-side" SPECT/CT analysis for neoplasm anatomic localization and diagnostic confidence. Therefore, SPECT/CT fusion should be performed routinely because it potentially influences clinical decision-making and patient management.

Imaging of neuroendocrine tumors

Neuroendocrine tumors (NETs) are rare neoplasms, which are characterized by the presence of neuroamine uptake mechanisms and/or peptide receptors at the cell membrane and these features constitute the basis of the clinical use of specific radiolabeled ligands, both for imaging and therapy. Radiolabeled metaiodobenzylguanidine (MIBG) was the first radiopharmaceutical used to specifically depict and localize catecholamine-secreting tumors (pheochromocytomas, paragangliomas, and neuroblastomas) and is still regarded as a first-choice imaging technique for diagnosis and follow-up; in patients with malignant disease, MIBG scintigraphy is an essential step to select patients for (131)I-MIBG therapy. Scintigraphy with (111)In- or (99m)Tc-labeled somatostatin analogs has become the main imaging technique for NETs, particularly those expressing a high density of somatostatin receptors, such as gastroenteropancreatic tumors; this procedure is used routinely for localizing the primary tumor, evaluating disease extension, monitoring the effect of treatment and for selecting patients for radioreceptor therapy. Since the recent development of hybrid machines, it has been possible to obtain images that simultaneously hold both anatomic (computed tomography [CT]) and functional (single-photon emission computed tomography [SPECT] or positron emission tomography [PET]) information, with great impact on diagnostic accuracy. Significant improvements have been made during the past few years with the development of highly specific radiopharmaceuticals for PET studies that reflect the different metabolic pathways of NETs, such as glucose metabolism ((18)F-fluorodeoxyglucose), the uptake of hormone precursors ((11)C-5-hydroxytryptophan, (11)C- or (18)F-dihydroxyphenylalanine, (18)F-fluorodopamine), the expression of receptors ((68)Ga-labeled somatostatin analogs), as well as the synthesis, storage, and release of hormones ((11)C-hydroxyephedrine and others). Among these radiopharmaceuticals, (68)Ga-labeled somatostatin analogs are increasingly used in specialized centers in Europe for PET and PET/CT imaging and show very promising results with high diagnostic sensitivity. New somatostatin analogs with different receptor affinity as well as other peptides are currently under investigation and will further improve our diagnostic and therapeutic capabilities in the future.

Single-Photon Emission Computed Tomography/Computed Tomography in Abdominal Diseases

Single-photon emission computed tomography (SPECT) studies of the abdominal region are established in conventional nuclear medicine because of their easy and large availability, even in the most peripheral hospitals. It is well known that SPECT imaging demonstrates function, rather than anatomy. It is useful in the diagnosis of various disorders because of its ability to detect changes caused by disease before identifiable anatomic correlates and clinical manifestations exist. However, SPECT data frequently need anatomic landmarks to precisely depict the site of a focus of abnormal tracer uptake and the structures containing normal activity; the fusion with morphological studies can furnish an anatomical map to scintigraphic findings. In the past, software-based fusion of independently performed SPECT and CT or magnetic resonance images have been demonstrated to be time consuming and not useful for routine clinical employment. The recent development of dual-modality integrated imaging systems, which provide SPECT and CT images in the same scanning session, with the acquired images co-registered by means of the hardware, has created a new scenario. The first data have been mainly reported in oncology patients and indicate that SPECT/CT is very useful because it is able to provide further information of clinical value in several cases. In SPECT studies of abdominal diseases, hybrid SPECT/CT can play a role in the differential diagnosis of hepatic hemangiomas located near vascular structures, in precisely detecting and localizing active splenic tissue caused by splenosis in splenectomy patients, in providing important information for therapy optimization in patients submitted to hepatic arterial perfusion scintigraphy, in accurately identifying the involved bowel segments in patients with inflammatory bowel diseases, and in correctly localizing the bleeding sites in patients with gastrointestinal bleeding.

Optimized scintigraphic evaluation of infection and inflammation: role of single-photon emission computed tomography/computed tomography fusion imaging

Gallium-67 citrate and radiolabeled white blood cells have become standard inflammation/infection-seeking agents whereas other agents, such as (99m)Tc diphosphonates, commonly are used to infer an infectious process. These radiopharmaceuticals reflect physiologic and pathologic function rather than anatomical abnormality. In the clinical setting, it is often necessary to correlate these functional studies with anatomical imaging. The advent of single-photon emission computed tomography, as well as positron emission tomography, provides tomographic images for direct correlation to anatomic modalities such as computed tomography and magnetic resonance imaging. The methods by which these functional and anatomic imaging modalities are correlated include side-by-side, software, and hardware fusion. Clinically, fusion imaging has been applied primarily to oncologic and neurologic applications. The literature supports the premise that multimodality fusion would increase the specificity of the physiologic modality and increase the sensitivity of the anatomic modality. Our institution uses software fusion to aid in the diagnosis of infection and inflammation. Through case vignettes, we illustrate applications for single-photon emission computed tomography/computed tomography fusion for the diagnosis of infection and inflammation in multiple organ systems.

Single-photon emission computed tomography/computed tomography in endocrinology

The introduction of fusion of functional and anatomical imaging modalities into the field of endocrinology led to a major breakthrough in diagnosis, staging, and follow-up of patients with endocrine tumors. The management of endocrine tumors is based on a wide variety of conventional techniques, including computed tomography, ultrasound, or magnetic resonance imaging, and on scintigraphic functional techniques, associated with unique uptake and transport mechanisms and with the presence of high density of membrane receptors on some of these tumors. Anatomical modalities provide accurate detection and localization of morphological abnormalities, whereas nuclear medicine studies reflect the pathophysiological status of the disease process. Lack of structural delineation and relatively low contrast hamper the precise anatomical localization of the abnormal functional findings in the presence of potential concurrent foci related to the physiological biodistribution of the radiotracer or to processes unrelated to the evaluated disease entity. The notion that anatomical high-resolution and functional imaging data act as complementary methods led to various combination techniques of these modalities. However, coregistration of the functional and anatomical data after the acquisition of the 2 imaging modalities on separate machines, in different sessions, fails to provide accurate alignment of data, and the mathematical modeling is too cumbersome to be used on a routine basis. In contrast, hybrid imaging devices of single-photon emission computed tomography/computed tomography in a single gantry enable the sequential acquisition of the two modalities, with subsequent merging of data into a composite image display. These hybrid studies have led to a revolution in the field of imaging, providing clinically relevant information that is not apparent on separate images. The present review evaluates the contribution of the integrated single-photon emission computed tomography/computed tomography technology to image analysis and management of patients with endocrine tumors.

Single-Photon Emission Computed Tomography/Computed Tomography in Lung Cancer and Malignant Lymphoma

In nuclear oncology, despite the fast-growing diffusion of (18)F-fluorodeoxyglucose positron emission tomography (FDG-PET), single-photon emission computed tomography (SPECT) studies can still play an useful clinical role in several applications. The main limitation of SPECT imaging with tumor-seeking agents is the lack of the structural delineation of the pathologic processes they detect; this drawback sometimes renders SPECT interpretation difficult and can diminish its diagnostic accuracy. Fusion with morphological studies can overcome this limitation by giving an anatomical map to scintigraphic data. In the past, software-based fusion of independently performed SPECT and CT images proved to be time-consuming and impractical for routine use. The recent development of dual-modality integrated imaging systems that provide functional (SPECT) and anatomical (CT) images in the same scanning session, with the acquired images coregistered by means of the hardware, has opened a new era in this field. The first reports indicate that SPECT/CT is very useful in cancer imaging because it is able to provide further information of clinical value in several cases. In SPECT, studies of lung cancer and malignant lymphomas using different radiopharmaceutical, hybrid images are of value in providing the correct localization of tumor sites, with a precise detection of the involved organs, and the definition of their functional status, and in allowing the exclusion of disease in sites of physiologic tracer uptake. Therefore, in lung cancer and lymphomas, hybrid SPECT/CT can play a role in the diagnosis of the primary tumor, in the staging of the disease, in the follow-up, in the monitoring of therapy, in the detection of recurrence, and in dosimetric estimations for target radionuclide therapy.

Anatomical accuracy of hybrid SPECT/spiral CT in the lower spine

AIM

The anatomical accuracy of hardware-based registration of skeletal single photon emission computed tomography (SPECT) and X-ray computerized tomography (CT) has as yet not been studied. The aim of this study was to evaluate this variable in the lower spine for a newly introduced hybrid SPECT/spiral-CT camera.

METHODS

In 22 patients referred for degenerative joint disease or tumours, whole-body bone scintigraphy including hybrid SPECT/spiral CT of the lower spine was performed. Subsequent analyses were performed on these pairs of images as well as on data sets obtained after using a rigid automated fusion procedure in addition. Two observers independently measured the distances between the visually determined centres of gravity of the CT and SPECT representation of the fourth and fifth lumbar vertebral body in the X-, Y- and Z-directions (X-, Y- and Z-distances).

RESULTS

The distances determined by the two observers for the two vertebral bodies correlated significantly and were averaged for further analysis. For hybrid SPECT/spiral CT without consecutive automated registration, the mean X-, Y- and Z-distances were 1.6+/-1.9 mm, 1.7+/-1.3 mm and 0.9+/-0.5 mm, respectively. Additional automated registration lowered these values to 1.2+/-0.9 mm, 1.1+/-0.7 mm and 0.8+/-0.4 mm, respectively. The difference for the Y-distance proved statistically significant (P<0.05). Additional automated registration significantly reduced the number of subjects in whom at least one of the distances determined was greater than the SPECT pixel size of 4.6 mm from 14% (n=3) to 0% (P<0.05).

CONCLUSION

Hardware-based fusion between skeletal SPECT and CT offers a nearly perfect data match in the lower spine. The additional use of a tool for automated rigid registration has the potential to reduce the error of alignment even further and may be useful in patients with reduced compliance leading to movements between the two examinations.

Image fusion analysis of (99m)Tc-HYNIC-Tyr(3)-octreotide SPECT and diagnostic CT using an immobilisation device with external markers in patients with endocrine tumours

PURPOSE

The aim of this study was to assess the value of multimodality imaging using a novel repositioning device with external markers for fusion of single-photon emission computed tomography (SPECT) and computed tomography (CT) images. The additional benefit derived from this methodological approach was analysed in comparison with SPECT and diagnostic CT alone in terms of detection rate, reliability and anatomical assignment of abnormal findings with SPECT.

METHODS

Fifty-three patients (30 males, 23 females) with known or suspected endocrine tumours were studied. Clinical indications for somatostatin receptor (SSTR) scintigraphy (SPECT/CT image fusion) included staging of newly diagnosed tumours (n=14) and detection of unknown primary tumour in the presence of clinical and/or biochemical suspicion of neuroendocrine malignancy (n=20). Follow-up studies after therapy were performed in 19 patients. A mean activity of 400 MBq of (99m)Tc-EDDA/HYNIC-Tyr(3)-octreotide was given intravenously. SPECT using a dual-detector scintillation camera and diagnostic multi-detector CT were sequentially performed. To ensure reproducible positioning, patients were fixed in an individualised vacuum mattress with modality-specific external markers for co-registration. SPECT and CT data were initially interpreted separately and the fused images were interpreted jointly in consensus by nuclear medicine and diagnostic radiology physicians.

RESULTS

SPECT was true-positive (TP) in 18 patients, true-negative (TN) in 16, false-negative (FN) in ten and false-positive (FP) in nine; CT was TP in 18 patients, TN in 21, FP in ten and FN in four. With image fusion (SPECT and CT), the scan result was TP in 27 patients (50.9%), TN in 25 patients (47.2%) and FN in one patient, this FN result being caused by multiple small liver metastases; sensitivity was 95% and specificity, 100%. The difference between SPECT and SPECT/CT was statistically as significant as the difference between CT and SPECT/CT image fusion (P<0.001). Twenty-seven abnormal SPECT findings in 17 patients could not be initially assigned to organs, but were clearly delineated after image fusion. In 21 patients (40%), clinically relevant information was obtained by image fusion as compared with SPECT alone.

CONCLUSION

Co-registration of SPECT and diagnostic CT using a cost-effective immobilisation device provides excellent accuracy for tumour detection of endocrine malignancies and is superior to SPECT and CT alone. Image fusion reduces false positive results and can detect additional lesions. Anatomical information provided by CT enables precise localisation of abnormalities observed in SPECT.

67Ga-SPECT/CT with a hybrid system in the clinical management of lymphoma

PURPOSE

The purpose of this study was to investigate the added value of co-registered fusion imaging using a hybrid system in patients with lymphoma.

METHODS

Twenty-four lymphoma patients underwent (67)Ga-SPECT/CT using a hybrid tomograph consisting of a dual-head, variable-angle gamma camera and a low-dose X-ray tube. Results were compared with those of SPECT alone.

RESULTS

Forty-five lesions were identified by SPECT alone, while 49 were detected by SPECT/CT. Forty out of the 45 lesions observed on SPECT were confirmed as lymphoma, but five were due to other causes (thoracic aorta blood pool activity, sialoadenitis in the submandibular gland, bowel activity, rib fracture and bone marrow activation due to radiotherapy). SPECT/CT identified nine more neoplastic lesions compared with SPECT alone: four areas of radiopharmaceutical accumulation were observed in para-aortic lymph nodes, three in the spleen, one in the liver and one in para-iliac lymph nodes. In five cases, SPECT/CT provided additional anatomical information over SPECT alone. In four patients, four large areas of (67)Ga uptake (one mediastinal, two supraclavicular and one para-aortic) were better characterised; in one subject uptake was localised in the seventh thoracic vertebra only by SPECT/CT. Hybrid imaging provided additional data in 13 patients (54.2%), thus inducing oncologists to reconsider the therapeutic approach in eight subjects (33.2%): unnecessary treatment was avoided in four (16.6%) while therapy was altered in another four (16.6%).

CONCLUSION

SPECT/CT hybrid system is able to provide information not obtained by SPECT alone. It allows the anatomical localisation of lymphoma and physiological radiopharmaceutical uptake, facilitates the diagnosis of tumours located in the abdomen (subdiaphragmatic lesions) and provides information that may cause a change in therapeutic strategy.