FDG-PET/MRI for the preoperative diagnosis and staging of peritoneal carcinomatosis: a prospective multireader pilot study.

PURPOSE: To assess the diagnostic performance of FDG-PET/MRI for the preoperative diagnosis and staging of peritoneal carcinomatosis (PC) using surgical Sugarbaker's PC index (PCI) as the reference in a multireader pilot study. METHODS: Fourteen adult patients (M/F: 3/11, mean age: 57 ± 12 year) with PC were prospectively included in this single-center study. Patients underwent FDG-PET/MRI prior to surgery (mean delay: 14 d, range: 1-63 d). Images were reviewed independently by 2 abdominal radiologists and 2 nuclear medicine physicians. The radiologists assessed contrast-enhanced abdominal MR images, while the nuclear medicine physicians assessed PET images fused with T2-weighted images. The abdomen was divided in 13 regions, scored from 0 to 3. A hybrid FDG-PET/MRI radiological PCI was created by combining the study data. Radiological PCI was compared to the surgical PCI on a per-patient and per-region basis. Inter-reader agreement was evaluated. RESULTS: Mean surgical PCI was 10 ± 8 (range: 0-24). Inter-reader agreement was almost perfect for all sets for radiologic PCI (Kappa: 0.81-0.98). PCI scores for all reading sets significantly correlated with the surgical PCI score (r range: 0.57-0.74, p range: < 0.001-0.003). Pooled per-patient sensitivity, specificity, and accuracy were 75%/50%/71.4% for MRI, 66.7%/50%/64.3% for FDG-PET, and 91.7%/50%/85.7% for FDG-PET/MRI, without significant difference (p value range 0.13-1). FDG-PET/MRI achieved 100% sensitivity and 100% specificity for a cutoff PCI of 20. Per-region sensitivity and accuracy were lower: 37%/61.8% for MRI, 17.8%/64.3% for FDG-PET, and 52.7%/60.4% for FDG-PET/MRI, with significantly higher sensitivity for FDG-PET/MRI. Per-region specificity was higher for FDG-PET (95%) compared to MRI (78.4%) and FDG-PET/MRI (66.5%). CONCLUSION: FDG-PET/MRI achieved an excellent diagnostic accuracy per-patient and weaker performance per-region for detection of PC. The added value of PET/MRI compared to MRI and FDG-PET remains to be determined.

The effect of pyridostigmine on small intestinal bacterial overgrowth (SIBO) and plasma inflammatory biomarkers in HIV-associated autonomic neuropathies.

Small intestinal bacterial overgrowth (SIBO) is common among patients with HIV-associated autonomic neuropathies (HIV-AN) and may be associated with increased bacterial translocation and elevated plasma inflammatory biomarkers. Pyridostigmine is an acetylcholinesterase inhibitor which has been used to augment autonomic signaling. We sought preliminary evidence as to whether pyridostigmine could improve proximal gastrointestinal motility, reduce SIBO, reduce plasma sCD14 (a marker of macrophage activation and indirect measure of translocation), and reduce the inflammatory cytokines IL-6 and TNFα in patients with HIV-AN. Fifteen participants with well-controlled HIV, HIV-AN, and SIBO were treated with 8 weeks of pyridostigmine (30 mg PO TID). Glucose breath testing for SIBO, gastric emptying studies (GES) to assess motility, plasma sCD14, IL-6, and TNFα, and gastrointestinal autonomic symptoms were compared before and after treatment. Thirteen participants (87%) experienced an improvement in SIBO following pyridostigmine treatment; with an average improvement of 50% (p = 0.016). There was no change in gastrointestinal motility; however, only two participants met GES criteria for gastroparesis at baseline. TNFα and sCD14 levels declined by 12% (p = 0.004) and 19% (p = 0.015), respectively; there was no significant change in IL-6 or gastrointestinal symptoms. Pyridostigmine may ameliorate SIBO and reduce levels of sCD14 and TNFα in patients with HIV-AN. Larger placebo-controlled studies are needed to definitively delineate how HIV-AN affects gastrointestinal motility, SIBO, and systemic inflammation in HIV, and whether treatment improves clinical outcomes.

Quantitative comparison of pre-therapy 99mTc-macroaggregated albumin SPECT/CT and post-therapy PET/MR studies of patients who have received intra-arterial radioembolization therapy with 90Y microspheres.

OBJECTIVE: The aim of our study was to compare yttrium -90 (90Y) dosimetry obtained from pre-therapy 99mTc-macroaggregated albumin (MAA) SPECT/CT versus post-therapy PET/MRI imaging among patients with primary or metastatic hepatic tumors. MATERIALS AND METHODS: Prior to 90Y radioembolization (RE), 32 patients underwent a scan using MAA mimicking 90Y distribution. After RE with 90Y microspheres, the patients were imaged on a PET/MRI system. Reconstructed images were transferred to a common platform and used to calculate 90Y dosimetry. The Passing-Bablok regression scatter diagram and the Bland and Altman method were used to analyze the difference between dosimetry values. RESULTS: For MAA and PET/MRI modalities, the mean liver doses for all 32 subjects were 43.0 ±â€¯20.9 Gy and 46.5 ±â€¯22.7 Gy, respectively, with a mean difference of 3.4 ±â€¯6.2 Gy. The repeatibility coefficient was 12.1 (27.0% of the mean). The Spearman rank correlation coefficient was high (ρ = 0.92). Although, there was a substantial difference in the maximum doses to the liver between the modalities, the mean liver doses were relatively close, with a difference of 24.0% or less. CONCLUSIONS: The two main contributors to the difference between dosimetry calculations using MAA versus 90Y PET/MRI can be attributed to the changes in catheter positioning as well as the liver ROIs used for the calculations. In spite of these differences, our results demonstrate that the dosimetry values obtained from pre-therapy MAA SPECT/CT scans and PET/MRI post-therapy 90Y studies were not significantly different.

Treatment of Primary Liver Tumors and Liver Metastases, Part 1: Nuclear Medicine Techniques.

90Y radioembolization is an increasingly used treatment for both primary and metastatic malignancy in the liver. Understanding the biophysical properties, dosing concerns, and imaging appearance of this treatment is important for interventional radiologists and nuclear medicine physicians to provide important therapy. 90Y radioembolization is efficacious and safe, although the possibility of complications does exist. This article provides a comprehensive in-depth discussion about the indications for 90Y radioembolization, reviews the role of preprocedural angiography and 99mTc-macroaggregated albumin scans, illustrates different dosing techniques, compares and contrasts resin and glass microspheres, and describes potential complications.

Comparison of PET/CT and PET/MR imaging and dosimetry of yttrium-90 (90Y) in patients with unresectable hepatic tumors who have received intra-arterial radioembolization therapy with 90Y microspheres.

BACKGROUND: The aim of our study was to compare 90Y dosimetry obtained from PET/MRI versus PET/CT post-therapy imaging among patients with primary or metastatic hepatic tumors. First, a water-filled Jaszczak phantom containing fillable sphere with 90Y-chloride was acquired on both the PET/CT and PET/MRI systems, in order to check the cross-calibration of the modalities. Following selective internal radiation therapy (SIRT) with 90Y microspheres, 32 patients were imaged on a PET/CT system, immediately followed by a PET/MRI study. Reconstructed images were transferred to a common platform and used to calculate 90Y dosimetry. A Passing-Bablok regression scatter diagram and the Bland and Altman method were used to analyze the difference between the dosimetry values. RESULTS: The phantom study showed that both modalities were calibrated with less than 1% error. The mean liver doses for the 32 subjects calculated from PET/CT and PET/MRI were 51.6 ± 24.7 Gy and 46.5 ± 22.7 Gy, respectively, with a mean difference of 5.1 ± 5.0 Gy. The repeatability coefficient was 9.0 (18.5% of the mean). The Spearman rank correlation coefficient was very high, ρ = 0.97. Although the maximum dose to the liver can be significantly different (up to 40%), mean liver doses from each modalities were relatively close, with a difference of 18.5% or less. CONCLUSIONS: The two main contributors to the difference in 90Y dosimetry calculations using PET/CT versus PET/MRI can be attributed to the differences in regions of interest (ROIs) and differences attributed to attenuation correction. Due to the superior soft-tissue contrast of MRI, liver contours are usually better seen than in CT images. However, PET/CT provides better quantification of PET images, due to better attenuation correction. In spite of these differences, our results demonstrate that the dosimetry values obtained from PET/MRI and PET/CT in post-therapy 90Y studies were similar.

Vagal dysfunction and small intestinal bacterial overgrowth: novel pathways to chronic inflammation in HIV.

OBJECTIVE: Chronic inflammation in HIV-infected individuals drives disease progression and the development of comorbidities, despite viral suppression with combined antiretroviral therapy. Here, we sought evidence that vagal dysfunction, which occurs commonly as part of HIV-associated autonomic neuropathy, could exacerbate inflammation through gastrointestinal dysmotility, small intestinal bacterial overgrowth (SIBO), and alterations in patterns of soluble immune mediators. DESIGN: This is a cross-sectional observational study. METHODS: Forty participants on stable combined antiretroviral therapy with gastrointestinal symptoms, and no causes for vagal or gastrointestinal dysfunction other than HIV, underwent autonomic testing, hydrogen/methane breath testing for SIBO, and gastric emptying scintigraphy. A panel of 41 cytokines, high-mobility group box 1, and markers of bacterial translocation (lipopolysaccharide) and monocyte/macrophage activation (sCD14 and sCD163) were tested in plasma. RESULTS: We found that participants with vagal dysfunction had delayed gastric emptying and higher prevalence of SIBO. SIBO was associated with IL-6, but not sCD14; lipopolysaccharide could not be detected in any participant. We also found alteration of cytokine networks in participants with vagal dysfunction, with stronger and more numerous positive correlations between cytokines. In the vagal dysfunction group, high mobility group box 1 was the only soluble mediator displaying strong negative correlations with other cytokines, especially those cytokines that had numerous other strong positive correlations. CONCLUSION: The current study provides evidence that the vagal component of HIV-associated autonomic neuropathy is associated with changes in immune and gastrointestinal function in individuals with well treated HIV. Further study will be needed to understand whether therapies targeted at enhancing vagal function could be of benefit in HIV.

Evaluation of diabetic foot infection in nuclear medicine.

Diabetic foot infection is not only the most common cause of hospitalization among diabetic patients, but is also associated with high morbidity, mortality and major utilization of the resources. Managing diabetic patients with suspected foot infection is highly dependent on an early and accurate determination of its presence and location. Medical imaging is often used in the workup of these patients, as clinical diagnosis of osteomyelitis is often difficult, and invasive bone biopsy is infrequently used due to many limitations. In this article, we review the role and accuracy of commonly used medical imaging modalities in the evaluation of diabetic patients with suspected foot infection including osteomyelitis with particular emphasis on molecular nuclear medicine imaging. The impact of imaging on patients' management is also discussed. We finally comment on possible future directions in hybrid molecular imaging techniques.

The ideal dual-isotope imaging combination in evaluating patients with suspected infection of pelvic pressure ulcers.

INTRODUCTION: The successful management of infected pelvic pressure ulcer patients (PPUP) depends on the distinction between infections limited to soft tissue (STI) and those with underlying osteomyelitis (OM), which can be difficult to determine clinically. Dual-isotope (DI) comprehensive imaging has excellent accuracy in localizing diabetic foot infection and differentiating OM from STI with SPECT/CT utilization. In this study, we assess the accuracy and confidence of the different DI SPECT/CT imaging steps in PPUP with confirmed diagnoses. PATIENTS AND METHODS: Pelvic flow and blood pool imaging were followed by labeled white blood cell reinjection and Tc-99m hydroxymethylene-diphosphonate bone (bone scan) and In-111-leukocytes (white blood cell scan) DI planar and SPECT/CT (step 1) acquisitions. Tc-99m sulfur colloid (bone marrow scan)/WBCS SPECT/CT (step 2) images were obtained on the following day. DI step 1 planar, step 1 SPECT/CT, step 2 SPECT/CT, and combined step 1/step 2 SPECT/CT were reviewed separately for diagnosis and diagnosis confidence. The final diagnosis was confirmed by culture/pathology in 21 patients and clinical/imaging follow-up in 12 patients. RESULTS: There were 19 OM patients, three STI patients, and 11 patients with no infection. The final diagnosis agreement to DI combined step 1/step 2 SPECT/CT was higher than DI step 2 or step 1 SPECT/CT alone, or DI step 1 planar, as assessed by λ and error reduction %, respectively. Combined DI step 1/step 2 SPECT/CT was more sensitive than DI step 2 SPECT/CT and more specific than DI step 1 SPECT/CT, and showed higher diagnostic confidence than both imaging techniques. CONCLUSION: DI SPECT/CT is highly useful in evaluating PPUP with suspected infection. DI step 1 is more sensitive, whereas step 2 is more specific. Both step 1 and step 2 DI SPECT/CT images are needed to accurately and confidently assess for infection and distinguish OM from STI, which are crucial for optimal management.

Direct comparison of neck pinhole dual-tracer and dual-phase MIBI accuracies with and without SPECT/CT for parathyroid adenoma detection and localization.

INTRODUCTION: There is uncertainty about accuracies of dual-phase (DP) and dual-tracer (DT) parathyroid scintigraphy with the newly added SPECT/CT. Although SPECT/CT was shown to be helpful in parathyroid adenoma (PA) localization, it may not have optimal resolution as pinhole. This study directly compared diagnostic accuracies and confidences of various imaging protocols on same patients. PATIENTS AND METHODS: One hundred fifty-five patients with pathologically confirmed diagnosis were included. Pinhole DP, pinhole DT, pinhole DP SPECT/CT, pinhole DT SPECT/CT, and SPECT/CT with only pinhole-delayed MIBI (D) were reviewed for accuracies and certainties of PA diagnosis/localization. Parathyroid adenomas were classified as clearly or unclearly distinguishable from thyroid. Furthermore, the contribution of pinhole DP to pinhole DT SPECT/CT was assessed. RESULTS: Of 153 PAs, the correct diagnosis/localization was significantly higher by pinhole DT SPECT/CT than pinhole DP SPECT/CT, SPECT/CT D, pinhole DT alone, and DP alone. Parathyroid adenomas were clearly more distinguished from thyroid in pinhole DT than DP with/without SPECT/CT. Consequently, PA diagnosis certainty was higher in pinhole DT than DP, whereas PA localization certainty was higher in both with SPECT/CT. In pinhole DT SPECT/CT, the pinhole DP addition confirmed diagnosis/localization of only 24 uncertain PAs. CONCLUSIONS: In this large patient group, the accuracy and certainty of PA diagnosis/localization were higher in pinhole DT SPECT/CT than all other parathyroid scintigraphy protocols. Pinhole DT better identified PA than pinhole DP, whereas SPECT/CT improved PA localization in both protocols. Pinhole DP showed limited contribution and thus should be only considered when PA diagnosis/localization is uncertain by pinhole DT SPECT/CT.

Dual-isotope SPECT/CT impact on hospitalized patients with suspected diabetic foot infection: saving limbs, lives, and resources.

BACKGROUND: Foot ulcer with suspected infection is one of the most common reasons for hospitalization and a major factor contributing to morbidity and high healthcare-related expenses among diabetic patients. Many patients will require amputation; however, major amputation is associated with an alarmingly high 5-year mortality rate. In this study, we assess the diagnosis and management of suspected foot infection in diabetic patients using dual-isotope (DI) single-photon emission computed tomography/computed tomography (SPECT/CT) compared with conventional imaging. METHODS: The diagnostic accuracy in and management of 227 patients who had undergone DI SPECT/CT was compared with that of 232 similar patients who had undergone conventional imaging including plain radiography, CT, planar bone scanning, planar indium-111 white blood cell scanning, and MRI. The duration of hospitalization was additionally compared between these two groups of patients after excluding patients with other active comorbidities. RESULTS: Soft-tissue infection, osteomyelitis with or without soft-tissue infection, and other bony pathologies were more accurately and confidently identified with DI SPECT/CT than with conventional imaging. DI SPECT/CT use was associated with significantly fewer major amputations and more selective bony resection as well as with shorter duration of hospitalization when compared with conventional imaging. CONCLUSION: In this large population of diabetic patients with suspected foot infection DI SPECT/CT was more accurate in diagnosing and localizing infection compared with conventional imaging. In addition, DI SPECT/CT provided clear guidance and promoted many limb salvage procedures. Of equal importance to health economics, DI SPECT/CT use was associated with considerably reduced length of hospitalization compared with conventional imaging.

Mycobacterial pseudotumor of the plantar fascia: how common is it?

Mycobacterial spindle cell pseudotumor (MSCP) is an extremely rare complication of mycobacterial infections. It has been reported to occur in various sites such as skin, lymph nodes, bone marrow, lungs, and spleen. This tumor-like lesion can be confused clinically as well as radiographically with dermatofibroma, nodular fasciitis, xanthogranuloma, and Kaposi's sarcoma. While this lesion is rare and has been previously reported to occur only in superficial skin, we emphasize its consideration and inclusion in the differential diagnoses when a deep soft tissue mass is complicated by symptoms of deep tissue infection secondary to abscess formation in immunocompromised hosts. Here, we present the clinical and radiologic findings of a case of MSCP involving the deep plantar sheaths.

Characterization of extrahepatic distribution of Tc-99m macroaggregated albumin in hepatic perfusion imaging studies prior to yttrium-90 microsphere therapy.

Tc-99m macroaggregated albumin (MAA) hepatic perfusion study and hepatic angiography are routinely performed prior to yttrium-90 (Y-90) microsphere therapy for patients with hepatocellular carcinoma (HCC) or metastatic cancers to the liver. The purpose of this study was to examine the incidence of altered Tc-99m MAA distribution in these patients and to identify factors that are associated with these changes. A total of 176 Tc-99m MAA hepatic perfusion studies in 159 patients performed in preparation for Y-90 microsphere therapy were retrospectively reviewed. Abnormal findings were identified and correlated with diagnosis, infusion site, tumor volume, and tumor uptake by using bivariate statistical analysis. Abnormal Tc-99m MAA distribution on the hepatic perfusion imaging studies include excessive hepatopulmonary shunting with an elevated shunting fraction (>10%; n=23, 13%) and abnormal intra-abdominal visceral deposition in the GI tract, pancreas, spleen, and umbilical vein (n=19; 11%). Patients with a diagnosis of HCC showed higher incidence of abnormal hepatopulmonary shunting compared with other types of tumors (p<0.05). The incidence of abnormal intra-abdominal visceral deposition is higher with infusion into the left hepatic artery or proper hepatic artery/common hepatic artery compared with infusion into right hepatic artery (p<0.001). In 9 of 12 cases with abnormal deposition in the stomach, duodenum, or pancreas, the cause was identified upon reviewing angiography retrospectively and was subsequently corrected. In conclusion, the hepatic perfusion imaging study is an important imaging modality in preparation and guidance of Y-90 microsphere treatment.

Identification of urologic complications after kidney transplant.

Urologic complications after kidney transplant are important causes of morbidity, hospitalization, and transplant loss. We report 2 cases of clinically unsuspected urine extravasation after kidney transplant that were diagnosed accurately using SPECT/CT (single-photon emission computed tomography/computed tomography) radionuclide renal scan and corrected using surgery. These cases emphasize the value of dynamic radionuclide renal scan using SPECT/CT in the detection of urologic complications.

Role of FDG PET/CT in staging of recurrent ovarian cancer.

Ovarian cancer is the fifth leading cause of cancer death among women in the United States and has a high likelihood of recurrence despite aggressive treatment strategies. Detection and exact localization of recurrent lesions are critical for guiding management and determining the proper therapeutic approach, which may prolong survival. Because of its high sensitivity and specificity compared with those of conventional techniques such as computed tomography (CT) and magnetic resonance (MR) imaging, fluorine 18 fluorodeoxyglucose positron emission tomography (PET) combined with CT is useful for detection of recurrent or residual ovarian cancer and for monitoring response to therapy. However, PET/CT may yield false-negative results in patients with small, necrotic, mucinous, cystic, or low-grade tumors. In addition, in the posttherapy setting, inflammatory and infectious processes may lead to false-positive PET/CT results. Despite these drawbacks, PET/CT is superior to CT and MR imaging for depiction of recurrent disease.

Extraperitoneal urine leak after renal transplantation: the role of radionuclide imaging and the value of accompanying SPECT/CT - a case report.

BACKGROUND: The differentiation of the nature of a fluid collection as a complication of kidney transplantation is important for management and treatment planning. Early and delayed radionuclide renography can play an important role in the evaluation of a urine leak. However, it is sometimes limited in the evaluation of the exact location and extent of a urine leak. CASE PRESENTATION: A 71-year-old male who had sudden anuria, scrotal swelling and elevated creatinine level after cadaveric renal transplantation performed Tc-99 m MAG3 renography to evaluate the renal function, followed by an ultrasound which was unremarkable. An extensive urine leak was evident on the planar images. However, an exact location of the urine leak was unknown. Accompanying SPECT/CT images confirmed a urine leak extending from the lower aspect of the transplant kidney to the floor of the pelvic cavity, presacral region and the scrotum via right inguinal canal as well as to the right abdominal wall. CONCLUSIONS: Renal scintigraphy is very useful to detect a urine leak after renal transplantation. However, planar imaging is sometimes limited in evaluating the anatomical location and extent of a urine leak accurately. In that case accompanying SPECT/CT images are very helpful and valuable to evaluate the anatomical relationships exactly.

PET/CT evaluation of cervical cancer: spectrum of disease.

The prognosis of invasive cervical cancer is based on the stage, size, and histologic grade of the primary tumor and the status of the lymph nodes. Assessment of disease stage is essential in determining proper management in individual cases. In the posttherapy setting, the timely detection of recurrence is essential for guiding management and may lead to increased survival. However, the official clinical staging system of the International Federation of Gynecology and Obstetrics has inherent flaws that may lead to inaccurate staging and improper management. Combined positron emission tomography (PET)/computed tomography (CT) represents a major technologic advance, consisting of two integrated complementary modalities whose combined strength tends to overcome their respective weaknesses. PET/CT has higher sensitivity and specificity than do conventional anatomic modalities and is valuable in determining the extent of disease and detecting recurrent or residual tumor. The combination of 2-[fluorine-18]fluoro-2-deoxy-d-glucose PET with intravenous contrast material-enhanced high-resolution CT has proved useful for avoiding the interpretative weaknesses associated with either modality alone and in increasing the accuracy of staging or restaging. Nonetheless, accurate PET/CT interpretation requires a knowledge of the characteristics of disease spread or recurrence and an awareness of various imaging pitfalls if false interpretations are to be avoided.

The optimized evaluation of diabetic foot infection by dual isotope SPECT/CT imaging protocol.

Sequential Tc-99m hydroxymethylene-diphosphonate (HDP) 3-phase bone (BS) and In-111 leukocyte scanning (WBCS) have been frequently used to evaluate the diabetic foot, as nonosteomyelitis BS uptake is repeatedly observed and osteomyelitis (OM) in WBCS is often uncertain without BS correlation. Additionally, both modalities are limited in lesion localization because of low resolution and lack of anatomic details. We investigated a method that combined BS/WBCS, and if needed, WBCS/bone marrow scanning (BMS) using SPECT/CT to accurately diagnose/localize infection in a practical protocol. Blood flow/pool images were obtained followed by WBC reinjection and next day dual isotope (DI) BS/WBCS planar and SPECT/CT. BMS/WBCS SPECT/CT (step 2 DI) was obtained on the following day when images were suspicious for mid/hindfoot OM. Diagnosis accuracy and confidence were judged for the various imaging combinations. Diagnosis was classified as OM, soft tissue infection (STI), both OM/STI, and other/no bony pathology by microbiology/pathology or follow-up. Distinction between various diagnostic categories and overall OM diagnostic accuracy in 213 patients were higher for DI than WBCS or BS alone, and for DI SPECT/CT than DI planar or SPECT only. Diagnostic confidence/lesion site was significantly higher for DI SPECT/CT than other comparative imaging methods. In a group of 97 patients with confirmed microbiologic/pathologic diagnosis, similar results were attained. Step 2 DI SPECT/CT performed in 67 patients further improved diagnostic accuracy/confidence. DI SPECT/CT is a highly accurate modality that considerably improves detection and discrimination of STI and OM while providing precise anatomic localization in the diabetic foot. This combined imaging technique promises to beneficially impact diabetic patient care.

Quantitative comparison of yttrium-90 (90Y)-microspheres and technetium-99m (99mTc)-macroaggregated albumin SPECT images for planning 90Y therapy of liver cancer.

Yttrium-90 ((90)Y)-microspheres administered via the hepatic artery has been used for the treatment of unresectable primary or metastatic cancer in the liver. Prior to (90)Y therapy, however, the (90)Y administered activity and the percent shunting to lungs must be determined, most commonly by gamma camera imaging of technetium-99m ((99m)Tc)-macroaggregated albumin (MAA). The purpose of the current study was to identify and evaluate an objective measure of the correlation of (90)Y and MAA activity distributions and thus assess the reliability of MAA imaging for evaluation of (90)Y administered activity and tumor and liver radiation doses. The MAA study consisted of two acquisitions. After administration of 185 MBq of MAA, a partial-body or so-called breakthrough scan was performed in order to determine the percent shunting to lungs. Immediately after a breakthrough scan, a combined single-photon emission computed tomography (SPECT)/transmission computed tomography (CT) scanner was used to image MAA distribution in order to derived the prescribed (90)Y administered activity based on tumor and liver dosimetry. (90)Y SPECT/CT was performed 2-4 weeks later and activities used were in the range of 777-2,442 MBq. In order to compare (90)Y and MAA SPECT images, first the respective CT image sets were registered using a transform based on normalized mutual information. The transform thus derived was used to align the 90Y and MAA SPECT image sets, and the Spearman's (rho) rank correlation as well as image distance (L2-norm) between the registered SPECT images were then calculated. The Spearman's rank correlation values ranged from 0.451 to 0.818 and the L2 distances from 0.626 to 2.889. Based on visual inspection, the registration of the (90)Y and MAA SPECT images appeared reasonably accurate. The regression coefficient (r) between visual scoring and the Spearman's rank correlation was 0.65 and between visual scoring and L2 distance 0.61. The Spearman's rank correlation thus appears to be more reliable than the image distance for assessing the correlation of the (90)Y and MAA images.