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

Applying standardized uptake values in gallium-67-citrate single-photon emission computed tomography/computed tomography studies and their correlation with blood test results in representative organs

OBJECTIVES

Recently, semiquantitative analysis using standardized uptake value (SUV) has been introduced in bone single-photon emission computed tomography/computed tomography (SPECT/CT). Our purposes were to apply SUV-based semiquantitative analytic method for gallium-67 (Ga)-citrate SPECT/CT and to evaluate correlation between SUV of physiological uptake and blood test results in representative organs.

METHODS

The accuracy of semiquantitative method was validated using an National Electrical Manufacturers Association body phantom study (radioactivity ratio of sphere : background=4 : 1). Thereafter, 59 patients (34 male and 25 female; mean age, 66.9 years) who had undergone Ga-citrate SPECT/CT were retrospectively enrolled in the study. A mean SUV of physiological uptake was calculated for the following organs: the lungs, right atrium, liver, kidneys, spleen, gluteal muscles, and bone marrow. The correlation between physiological uptakes and blood test results was evaluated using Pearson's correlation coefficient.

RESULTS

The phantom study revealed only 1% error between theoretical and actual SUVs in the background, suggesting the sufficient accuracy of scatter and attenuation corrections. However, a partial volume effect could not be overlooked, particularly in small spheres with a diameter of less than 28 mm. The highest mean SUV was observed in the liver (range: 0.44-4.64), followed by bone marrow (range: 0.33-3.60), spleen (range: 0.52-2.12), and kidneys (range: 0.42-1.45). There was no significant correlation between hepatic uptake and liver function, renal uptake and renal function, or bone marrow uptake and blood cell count (P>0.05).

CONCLUSION

The physiological uptake in Ga-citrate SPECT/CT can be represented as SUVs, which are not significantly correlated with corresponding blood test results.

Role of single photon emission computed tomography/computed tomography in diagnostic iodine-131 scintigraphy before initial radioiodine ablation in differentiated thyroid cancer

Objectives:

The study was performed to evaluate the incremental value of single photon emission computed tomography/computed tomography (SPECT/CT) over planar radioiodine imaging before radioiodine ablation in the staging, management and stratification of risk of recurrence (ROR) in differentiated thyroid cancer (DTC) patients.

Materials and Methods:

Totally, 83 patients (21 male, 62 female) aged 17–75 (mean 39.9) years with DTC were included consecutively in this prospective study. They underwent postthyroidectomy planar and SPECT/CT scans after oral administration of 37–114 MBq iodine-131 (I-131). The scans were interpreted as positive, negative or suspicious for tracer uptake in the thyroid bed, cervical lymph nodes and sites outside the neck. In each case, the findings on planar images were recorded first, without knowledge of SPECT/CT findings. Operative and pathological findings were used for postsurgical tumor–node–metastasis staging. The tumor staging was reassessed after each of these two scans.

Results:

Single photon emission computed tomography/computed tomography localized radioiodine uptake in the thyroid bed in 9/83 (10.8%) patients, neck nodes in 24/83 (28.9%) patients and distant metastases in 8/83 (9.6%) patients in addition to the planar study. Staging was changed in 8/83 (9.6%), ROR in 11/83 (13.2%) and management in 26/83 (31.3%) patients by the pretherapy SPECT/CT in comparison to planar imaging. SPECT/CT had incremental value in 32/83 patients (38.5%) over the planar scan.

Conclusion:

Single photon emission computed tomography/computed tomography is feasible during a diagnostic I-131 scan with a low amount of radiotracer. It improved the interpretation of pretherapy I-131 scintigraphy and changed the staging and subsequent patient management.

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.

Managing lymphoma with non-FDG radiotracers: current clinical and preclinical applications

Nuclear medicine imaging modalities such as positron emission tomography (PET) and single-photon emission computed tomography (SPECT) have played a prominent role in lymphoma management. PET with [(18)F]Fluoro-2-deoxy-D-glucose (FDG) is the most commonly used tool for lymphoma imaging. However, FDG-PET has several limitations that give the false positive or false negative diagnosis of lymphoma. Therefore, development of new radiotracers with higher sensitivity, specificity, and different uptake mechanism is in great demand in the management of lymphoma. This paper reviews non-FDG radiopharmaceuticals that have been applied for PET and SPECT imaging in patients with different types of lymphoma, with attention to diagnosis, staging, therapy response assessment, and surveillance for disease relapse. In addition, we introduce three radiolabeled anti-CD20 antibodies for radioimmunotherapy, which is another important arm for lymphoma treatment and management. Finally, the relatively promising radiotracers that are currently under preclinical development are also discussed in this paper.

Technetium-99m depreotide imaging by single photon emission tomography/low resolution computed tomography in malignant lymphomas: comparison with gallium-67 citrate

OBJECTIVE

Previous studies have demonstrated the feasibility of targeting lymphoma lesions with somatostatin receptor binding agents, mainly with In-111-pentetreotide. In the present work another somatostatin analog, Tc-99m depreotide, is investigated.

METHODS

One-hundred and six patients, 47 with Hodgkin's (HL) and 59 with various types of non-Hodgkin's lymphoma (NHL), were imaged with both Tc-99m depreotide and Ga-67 citrate. Planar whole-body and single photon emission tomography/low resolution computerized tomography (SPECT/CT) images were obtained. A total of 142 examinations were undertaken at different phases of the disease. Depreotide and gallium findings were compared visually and semi-quantitatively, with reference to the results of conventional work-up and the patients' follow-up data.

RESULTS

In most HL, intermediate- and low-grade B-cell, as well as in T-cell NHL, depreotide depicted more lesions than Ga-67 and/or exhibited higher tumor uptake. The opposite was true in aggressive B-cell NHL. However, there were notable exceptions in all lymphoma subtypes. During initial staging, 93.3% of affected lymph nodes above the diaphragm, 100% of inguinal nodes and all cases with splenic infiltration were detected by depreotide. On the basis of depreotide findings, 32% of patients with early-stage HL were upstaged. However, advanced HL and NHL cases were frequently downstaged, due to low sensitivity for abdominal lymph node (22.7%), liver (45.5%) and bone marrow involvement (36.4%). Post-therapy, depreotide detected 94.7% of cases with refractory disease or recurrence. Its overall specificity was moderate (57.1%). Rebound thymic hyperplasia, various inflammatory processes and sites of unspecific uptake were the commonest causes of false positive findings. The combination of depreotide and gallium enhanced sensitivity (100%), while various false positive results of either agent could be avoided.

CONCLUSION

Except perhaps for early-stage HL, Tc-99m depreotide as a stand-alone imaging modality has limited value for the initial staging of lymphomas. Post-therapy, however, depreotide scintigraphy seems useful in the evaluation of certain anatomic areas, particularly in non-aggressive lymphoma types. The combination with Ga-67 potentially enhances sensitivity and specificity. If fluorodeoxyglucose positron emission tomography is not available or in case of certain indolent lymphoma types, Tc-99m depreotide may have a role as an adjunct to conventional imaging procedures.

A review on the clinical uses of SPECT/CT

In the era when positron emission tomography (PET) seems to constitute the most advanced application of nuclear medicine imaging, still the conventional procedure of single photon emission computed tomography (SPECT) is far from being obsolete, especially if combined with computed tomography (CT). In fact, this dual modality imaging technique (SPECT/CT) lends itself to a wide variety of useful diagnostic applications whose clinical impact is in most instances already well established, while the evidence is growing for newer applications. The increasing availability of new hybrid SPECT/CT devices with advanced technology offers the opportunity to shorten acquisition time and to provide accurate attenuation correction and fusion imaging. In this review we analyse and discuss the capabilities of SPECT/CT for improving sensitivity and specificity in the imaging of both oncological and non-oncological diseases. The main advantages of SPECT/CT are represented by better attenuation correction, increased specificity, and accurate depiction of the localization of disease and of possible involvement of adjacent tissues. Endocrine and neuroendocrine tumours are accurately localized and characterized by SPECT/CT, as also are solitary pulmonary nodules and lung cancers, brain tumours, lymphoma, prostate cancer, malignant and benign bone lesions, and infection. Furthermore, hybrid SPECT/CT imaging is especially suited to support the increasing applications of minimally invasive surgery, as well as to precisely define the diagnostic and prognostic profile of cardiovascular patients. Finally, the applications of SPECT/CT to other clinical disorders or malignant tumours is currently under extensive investigation, with encouraging results in terms of diagnostic accuracy.

Impact on reader performance for lesion-detection/ localization tasks of anatomical priors in SPECT reconstruction

With increasing availability of multimodality imaging systems, high-resolution anatomical images can be used to guide the reconstruction of emission tomography studies. By measuring reader performance on a lesion detection task, this study investigates the improvement in image-quality due to use of prior anatomical knowledge, for example organ or lesion boundaries, during SPECT reconstruction. Simulated (67)Ga -citrate source and attenuation distributions were created from the mathematical cardiac-torso (MCAT) anthropomorphic digital phantom. The SIMIND Monte Carlo software was then used to generate SPECT projection data. The data were reconstructed using the De Pierro maximum a posteriori (MAP) algorithm and the rescaled-block-iterative (RBI) algorithm for comparison. We compared several degrees of prior knowledge about the anatomy: no knowledge about the anatomy; knowledge of organ boundaries; knowledge of organ and lesion boundaries; and knowledge of organ, lesion, and pseudo-lesion (non-emission uptake altering) boundaries. The MAP reconstructions used quadratic smoothing within anatomical regions, but not across any provided region boundaries. The reconstructed images were read by human observers searching for lesions in a localization receiver operating characteristic (LROC) study of the relative detection/localization accuracies of the reconstruction algorithms. Area under the LROC curve was computed for each algorithm as the comparison metric. We also had humans read images reconstructed using different prior strengths to determine the optimal trade-off between data consistency and the anatomical prior. Finally by mixing together images reconstructed with and without the prior, we tested to see if having an anatomical prior only some of the time changes the observer's detection/localization accuracy on lesions where no boundary prior is available. We found that anatomical priors including organ and lesion boundaries improve observer performance on the lesion detection/localization task. Use of just organ boundaries did not provide a statistically significant improvement in performance however. We also found that optimal prior strength depends on the level of anatomical knowledge, with a broad plateau in which observer performance is near optimal. We found no evidence that having anatomical priors use lesion boundaries only when available changes the observer's performance when they are not available. We conclude that use of anatomical priors with organ and lesion boundaries improves reader performance on a lesion-detection/localization task, and that pseudo-lesion boundaries do not hurt reader performance. However, we did not find evidence that a prior using only organ boundaries helps observer performance. Therefore we suggest prior strength should be tuned to the organ-only case, since a prior will likely not be available for all lesions.

Prognostic value of early 18 fluorodeoxyglucose positron emission tomography and gallium-67 scintigraphy in aggressive lymphoma: a prospective comparative study

The prognostic value of fluorodeoxyglucose positron emission tomography (FDG-PET) and gallium-67 scan (GS) performed early after chemotherapy was assessed in 40 patients with newly diagnosed aggressive lymphoma. FDG-PET and GS were performed before and after three cycles of CHOP (cyclophosphamide, doxorubicin, vincristine, prednisone) or two cycles of ACVBP (doxorubicin, cyclophosphamide, vindesine, bleomycin, prednisone), with or without rituximab. Thirty-five patients had diffuse large B-cell lymphoma (DLBCL), two had mantle-cell lymphoma and three had T-cell lymphoma. Four patients relapsed despite early negative FDG-PET and GS including all three patients with T-cell lymphoma. Nine patients stayed in remission despite positive FDG-PET and/or GS of whom five showed moderate intensity residual bone uptake. Seven of these nine early false positives had a negative exam at the end of treatment. In patients with DLBCL, the 2-year event-free survival was 85% for negative versus 30% for positive FDG-PET patients (P = 0.003) whereas it was 78% for negative versus 33% for positive GS patients (P = 0.018). Sensitivity, specificity and diagnostic accuracy of FDG-PET and GS were not significantly different: 90% versus 70%, 76 versus 80% and 80 versus 77%, respectively. We conclude that both FDG-PET and GS are valuable tools to early predict outcome in patients with DLBCL.

The role of single-photon emission computed tomography/computed tomography for precise localization of metastases in patients with differentiated thyroid cancer

PURPOSE

It is very important in the management of patients with differentiated thyroid cancer (DTC) to precisely localize the foci of I-131 uptake, but it is difficult because of a lack of anatomic landmarks. The purpose of this study was to investigate the added value of I-131 single-photon emission computed tomography (SPECT)/computed tomography (CT) fusion imaging using a hybrid system in patients with DTC.

METHODS

Ninety-four patients with DTC underwent I-131 SPECT/CT using a hybrid tomography consisting of a dual-head variable-angle gamma camera and a low-dose X-ray tube. Results were compared with I-131 whole-body scan (WBS). SPECT/CT was performed 5-7 days after administration of a therapeutic dose of I-131. Fusion images were constructed by combining the digital CT and SPECT images on a computer workstation.

RESULTS

Compared with I-131 WBS, SPECT/CT imaging had improved the precise localization in 21% (20/94) of patients. In addition, SPECT/CT provided additional clinical data in 12 of the patients examined (12/94) and also caused physicians to reconsider the (131)I therapeutic approach in 22 patients.

CONCLUSION

The results of the current study indicate that the addition of I-131 SPECT/CT to WBS can improve the localization of metastases in patients with DTC. It may also detect metastases missed by WBS and adjust the therapy plan.

Incremental value of 131I SPECT/CT in the management of patients with differentiated thyroid carcinoma

(131)I whole-body scintigraphy (WBS) is a highly sensitive method for the detection of differentiated thyroid tumors and metastases. However, a lack of anatomic landmarks and the physiologic accumulation of the tracer complicate interpretation of the images. This prospective study was designed to evaluate the incremental value of (131)I SPECT/CT over planar WBS in the management of patients with differentiated thyroid carcinoma (DTC).

METHODS

Planar imaging was performed on 66 consecutive DTC patients who were considered to have locally advanced or metastatic disease after total or nearly total thyroidectomy. SPECT/CT was added for patients whose planar findings were inconclusive. The planar images were interpreted by 2 experienced nuclear medicine physicians. Interpretation of the SPECT/CT images was a consensus opinion of one of the nuclear medicine physicians and an experienced radiologist. Fusion images were considered to improve image interpretation when they better localized sites of increased (131)I uptake. The final diagnosis was verified by pathologic findings, other imaging modalities, and clinical follow-up. Both site-based and patient-based analyses were performed, and the impact of SPECT/CT results on therapeutic strategy was assessed.

RESULTS

A total of 232 foci were observed by (131)I WBS, including 33.2% of foci localized in the thyroid bed, 62.1% due to malignant lesions, and 4.7% caused by nonthyroidal physiologic or benign uptake or a contaminant. Overall, 37 SPECT/CT studies were performed on 23 patients, whose planar images showed 81 inconclusive lesions. Precise localization and characterization of (131)I-avid foci were achieved through (131)I SPECT/CT in 69 (85.2%) and 67 (82.7%) of the 81 foci, respectively. Fusion images were considered to be of benefit in 17 (73.9%) of 23 patients. The therapeutic strategy was changed in 8 (47.1%) of 17 patients. Uncommon metastatic lesions were found in 9 (13.6%) of 66 patients with regard to SPECT/CT fusion images.

CONCLUSION

Fusion of SPECT and CT images was of incremental value over WBS in increasing diagnostic accuracy, reducing pitfalls, and modifying therapeutic strategies in 73.9% of DTC patients. As SPECT/CT techniques emerge, (131)I SPECT/CT may demonstrate higher value than WBS in the management of DTC.

Perspectives of molecular imaging and radioimmunotherapy in lymphoma

Successful treatment of Hodgkin lymphomas and non-Hodgkin lymphomas depends on accurate staging and prognostic estimations, as well as evaluation of response to therapy as early after initiation as possible. We focus on several aspects of molecular imaging and therapy that affect the management of patients who have lymphoma. First, we review prior use of gallium-67 citrate for evaluation of lymphoma patients, mainly from a historical perspective, since it was the mainstream lymphoma functional imaging tracer for decades. Next, we review current clinical uses of 18F Fluoro-2-Deoxyglucose (18F FDG) PET and PET/CT for evaluation of lymphoma patients and use of radioimmunotherapy in lymphoma. Finally, we discuss advances in molecular imaging that may herald the next generation of PET radiotracers after 18F FDG.

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.

Usefulness of 67Ga SPECT and integrated low-dose CT scanning (SPECT/CT) in the diagnosis of cardiac sarcoidosis

OBJECTIVE

We performed 67Gallium (Ga) single-photon emission computed tomography (SPECT) with integrated low-dose computed tomography (CT) for the interpretation of myocardial outline to investigate the value of co-registered fusion imaging using a hybrid system (SPECT/CT) in patients with cardiac sarcoidosis.

METHODS

SPECT/CT of the region in question was performed with VG Hawkeye. The subjects in this study were 37 patients [mean (+/-SD) age 61.0+/-13.0 years; 12 men and 25 women], 13 of whom had a clinical diagnosis of cardiac sarcoidosis and 24 a negative diagnosis. An intravenous injection of Ga (dosage 111 MBq) was performed on patients 48 h or 72 h before obtaining static planar images of the whole-body and the SPECT/CT scan.

RESULTS

Abnormal Ga uptake in the myocardium was observed in 10 of the 13 subjects with true sarcoidosis, and in 11 of 24 with negative sarcoidosis without CT fusion. The sensitivity without CT fusion was 77%, the specificity 54%, and the accuracy 62%. Use of SPECT/CT changed the diagnosis only in a patient with true sarcoidosis, and changed the diagnosis in eight patients with negative sarcoidosis. The sensitivity with CT fusion was 69%, the specificity 79%, and the accuracy 76%. The difference in diagnostic accuracy was statistically significant (McNemar's test, P=0.039).

CONCLUSIONS

SPECT scanning using Ga and integrated low-dose CT is a very useful diagnostic imaging technique because it improves the diagnostic specificity of Ga SPECT to allow the highly specific diagnosis of cardiac sarcoidosis.

A 18F-FDG-positive, 67Ga-negative, and transferrin receptor expression-negative patient with diffuse large B-cell lymphoma

We recently experienced a case with uveitis suffering from fever of unknown origin suspected of being caused by sarcoidosis. Chest computed tomography showed right supraclavicular, bilateral mediastinal, and right hilar lymphadenopathy, and intensive abnormal uptake of 2-[18F]fluoro-2-deoxy-D-glucose (18F-FDG) was observed on positron emission tomography with 18F-FDG (FDG-PET). On the other hand, 67Ga scintigraphy showed almost no abnormal findings. Histopathological examination revealed the lesion to be a diffuse large B-cell lymphoma (DLBCL), namely, an aggressive non-Hodgkin lymphoma from a right supraclavicular lymph node biopsy specimen. Additional immunohistochemical analysis showed the negative expression of transferrin receptor (TfR) on the formalin-fixed paraffin-embedded specimen. Although DLBCL is generally considered to be a 67Ga-avid tumor, it does not always have a large number of TfRs and that leads to a discrepancy between the 67Ga scintigraphy and FDG-PET findings. FDG-PET should be more appropriate for the initial staging of DLBCL than 67Ga scintigraphy, whereas 67Ga scintigraphy might be able to provide additional information including prognostic factors and to support strategies that target TfR for cancer therapy.

SPECT/CT imaging using a spiral CT scanner for anatomical localization: Impact on diagnostic accuracy and reporter confidence in clinical practice

PURPOSE

To evaluate the incremental benefit in routine clinical practice of computed tomography (CT) scans acquired for anatomical localization on an integrated SPECT/CT which incorporates a spiral CT scanner, in comparison with conventional planar and SPECT scanning.

METHODS

The first 50 studies acquired on the integrated system were evaluated by two experienced nuclear medicine physicians who were aware of the patient's clinical history. These included bone scans, gallium scans, octreotide scans, sestamibi parathyroid scans and MIBG scans. For each patient study, abnormalities were assessed on planar and SPECT images for location and provisional diagnosis and a quantitative scale was used to assess reporter confidence. The fused SPECT/CT images were then reviewed and the location and provisional diagnosis noted and reporter confidence was assessed using the same quantitative scale.

RESULTS

There were 129 abnormalities detected in 50 patient studies. For localization of abnormalities, the inclusion of the CT resulted in a minor change in 16% of cases and a significant change in 11% over planar/SPECT imaging alone. The confidence of localization was improved moderately in 19% and improved significantly in 6%. For diagnosis, SPECT/CT resulted in a minor change in 10% and a significant change in 9% over planar/SPECT imaging. The confidence of diagnosis was improved moderately in 10% and improved significantly in a further 10% of cases. For the final scan interpretation, there would have been no change in 44% patients, a minor change in 30% and a significant change in 26% with the use of SPECT/CT.

CONCLUSION

Use of integrated SPECT/CT with a high spatial resolution, spiral CT used for anatomical localization improves accuracy and reporter confidence in clinical practice. As a result, final reports were different in 56% of the cases, including being significantly different in 26% patients compared to reporting with planar/SPECT alone.

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.

Estudios SPECT-TAC con 67Ga de la enfermedad linfomatosa. Su aportación en la estadificación y seguimiento de la enfermedad

INTRODUCTION

67Ga scintigraphy is an established method for the staging and follow-up of patients diagnosed of lymphomas. The aim of this study is to evaluate advantages of 67Ga SPECT-CT study over planar, SPECT and high resolution CT studies in lymphoma disease.

MATERIAL AND METHODS

One hundred and one 67Ga studies corresponding to 74 patients (46 men) were obtained, mean age 44 years. Thirty-eight patients (51 %) were diagnosed of Hodgkin's lymphoma and 36 were non-Hodgkin's lymphoma. All patients were evaluated with 67Ga and high-resolution CT studies. 67Ga studies were performed in a hybrid system, obtaining planar, SPECT and fused SPECT-CT imaging. Findings obtained from 67Ga studies were correlated with findings obtained from CT studies, both much in number of tumoral lesions and in their localization.

RESULTS

Planar, SPECT, SPECT-CT and CT studies detected 123, 146, 155 and 132 lesions respectively. SPECT-CT and CT were concordant in 52 studies, while there was no concordance between SPECT-CT and CT in the remaining 49 studies, SPECT-CT detecting more lesions than CT in 28 of them. These findings changed the disease stage 18 times (18 % of whole studies).

CONCLUSION

These results show better efficiency of 67Ga SPECT-CT compared to the other acquisition methods of 67Ga study and to CT for detection of tumoral lymphomatous lesions. 67Ga SPECT-CT study improves the diagnostic yield of the study with 67Ga in patients with lymphoma, providing better anatomical localization of tumoral lesions and detection of extraganglionar disease.

Utilidad clínica de las imágenes de fusión 67Ga SPECT/TC en pacientes con linfoma

AIM

The aim of this work is to show the clinical utility of the fused SPECT 67Ga/CT images in patients with lymphoma.

MATERIAL AND METHOD

44 patients (22 male) with lymphoma have been studied. 22 with Hodgkin's disease and 22 with non Hodgkin lymphoma. 59 studies were performed (33 thorax-cervical [T], 24 abdomen [A] and 2 skull-cervical area [SC]) with an hybrid gammacamera Millenium VG. We acquire consecutively a whole body scan, a SPECT and a CT, for its fusion with the SPECT, of the affects areas. The images were evaluated by two experts blinded, who classify the contribution of the fusion of images respect to the SPECT like: non changes, it improves the location or changes the extension of the injuries and it changes the staging. Final lesion location was confirmed by a high resolution CT performed within one month.

RESULTS

32/59 studies did not change the location or extension of the injuries (20T, 12A), 23/59 studies changed the location or extension of the injuries (12T, 9A and 2 SC) and on 4/59 the change of location induced a change of staging respect to showed by the SPECT.

CONCLUSION

To make fused SPECT 67Ga/CT images in patients with lymphoma allows improving the diagnostic precision in a 46% of the cases, mainly in the abdominal, bone and of the diaphragmatic area studies.

Human-observer LROC study of lesion detection in Ga-67 SPECT images reconstructed using MAP with anatomical priors

We compare the image quality of SPECT reconstruction with and without an anatomical prior. Area under the localization-response operating characteristic (LROC) curve is our figure of merit. Simulated Ga-67 citrate images, a SPECT lymph-nodule imaging agent, were generated using the MCAT digital phantom. Reconstructed images were read by human observers.Several reconstruction strategies are compared, including rescaled block iterative (RBI) and maximum-a-posteriori (MAP) with various priors. We find that MAP reconstruction using prior knowledge of organ and lesion boundaries significantly improves lesion-detection performance (p < 0.05). Pseudo-lesion boundaries, regions without increased uptake which are incorrectly treated as prior knowledge of lesion boundaries, do not decrease performance.