Verification of the effect of acquisition time for SwiftScan on quantitative bone single-photon emission computed tomography using an anthropomorphic phantom.

BACKGROUND: SwiftScan single-photon emission computed tomography (SPECT) is a recently released scanning technique with data acquired when the detector is stationary and when it moves from one view to the next. The influence of scan time for using SwiftScan on quantitative bone SPECT remains unclear. This study aimed to clarify the effect of the scan time for SwiftScan SPECT on the image quality and quantification of bone SPECT compared to step and shoot mode (SSM) using 99mTc-filled anthropomorphic phantom (SIM2 bone phantom). MATERIALS AND METHODS: Phantom SPECT/computed tomography (CT) images were acquired using Discovery NM/CT 860 (GE Healthcare) with a low-energy high-resolution sensitivity collimator. We used the fixed parameters (subsets 10 and iterations 5) for reconstruction. The coefficient of variation (CV), contrast-to-noise ratio (CNR), full width at half maximum (FWHM), and quantitative value of SwiftScan SPECT and SSM were compared at various acquisition times (5, 7, 17, and 32 min). RESULTS: In the short-time scan (< 7 min), the CV and CNR of SwiftScan SPECT were better than those of SSM, whereas in the longtime scan (> 17 min), the CV and CNR of SwiftScan SPECT were similar to those of SSM. The FWHMs for SwiftScan SPECT (13.6-14.8 mm) and SSM (13.5-14.4 mm) were similar. The mean absolute errors of quantitative values at 5, 7, 17, and 32 min were 38.8, 38.4, 48.8, and 48.1, respectively, for SwiftScan SPECT and 41.8, 40.8%, 47.2, and 49.8, respectively, for SSM. CONCLUSIONS: SwiftScan on quantitative bone SPECT provides improved image quality in the short-time scan with quantification similar to or better than SSM. Therefore, in clinical settings, using SwiftScan SPECT instead of the SSM scan protocol in the short-time scan might provide higher-quality diagnostic images than SSM. Our results could provide vital information on the use of SwiftScan SPECT.

MRI diffusion-weighted imaging detects a fresh portal vein thrombus as a high intensity lesion in a patient with a liver transplant: A case report.

Portal vein thrombosis is one of the most serious complications after liver transplantation. It is important to determine the age of the thrombus for management of portal vein thrombosis. We present a case report of histologically confirmed heterogenous fresh portal vein thrombus which was depicted heterogenous high signal intensity on magnetic resonance diffusion weighted imaging. The sequence may be a useful imaging tool for detecting fresh thrombus components in the portal vein thrombosis.

High Signal Intensity on Diffusion-Weighted Images Reflects Acute Phase of Deep Vein Thrombus.

The effects of antithrombotic therapy on deep vein thrombosis (DVT) can be affected by thrombus age, which cannot be reliably determined by noninvasive imaging modalities. We investigated whether magnetic resonance (MR) diffusion-weighted imaging (DWI) can localize and determine the age of venous thrombus in patients with DVT, animal models, and human blood in vitro. Signal intensity (SI) on DWI and the apparent diffusion coefficient (ADC) of thrombi were assessed in eight patients with DVT using a 1.5-T MR imaging (MRI) system. We assessed the organizing processes as venous thrombus developed in the rabbit jugular vein using a 3.0-T MRI system over time. We also assessed MRI signals of human blood in vitro using the 1.5-T MRI system. Venous thrombi were detected by DWI as areas of high or mixed high and iso SI in all patients. The ADCs were lower in the proximal, than in the distal portion of the thrombi. The thrombi of rabbit jugular veins histologically organized in a time-dependent manner, with high SI on DWI at 4 hours, mixed high and iso SI at 1 and 2 weeks, and iso SI at 3 weeks. The ADC correlated negatively with erythrocyte content, and positively with smooth muscle cells, macrophages, hemosiderin, and collagen content. MRI signals of human blood in vitro showed that ADCs were affected by erythrocyte content, but not by blood clotting. MR-DWI can detect venous thrombus, and high SI on DWI accompanied by a low ADC might reflect erythrocyte-rich, acute-phase thrombi.

Therapeutic response of immunoglobulin 4-related aortitis and pancreatitis demonstrated by diffusion-weighted MRI.

Immunoglobulin (IgG) 4-related disease is a systemic inflammatory disease, and it affects vascular system as aortitis, periaortitis, or aneurysm. However, due to a lack of serum biomarker on aortic damage and the multiorgan involvement, it is difficult to assess aortic inflammatory activity of IgG4-related disease. We described a case of IgG4-related pancreatitis and aortitis, which was visualized with magnetic resonance merged image of diffusion weighted and T1 weighted images. The aortic signal intensity or apparent diffusion coefficient value reduced or increased after oral prednisone administration, respectively. Magnetic resonance diffusion weighted image and apparent diffusion coefficient may be a useful imaging tool for assessment of vascular inflammation in IgG4-related aortitis.

Coronary high-signal-intensity plaques on T1-weighted magnetic resonance imaging reflect intraplaque hemorrhage.

Coronary high-signal-intensity plaques (HIPs) detected by T1-weighted magnetic resonance imaging are associated with future cardiovascular events. This study aimed to identify pathological findings reflecting HIPs in coronary arteries obtained from autopsy cases. Formalin-fixed hearts were imaged with noncontrast T1-weighted imaging with a 1.5-T magnetic resonance system. We defined HIPs or non-HIPs as a coronary plaque to myocardial signal intensity ratio (PMR) of ≥1.4 or <1.4, respectively. We found HIPs in 4 of 37 (10.8%) hearts and analyzed 7 hearts in detail. The corresponding sections to HIPs (n=11) or non-HIPs (n=25) were histologically and immunohistochemically analyzed. We calculated the T1 relaxation time of human venous blood in vitro. Plaque and necrotic core areas, and the frequency of intraplaque hemorrhage in HIPs were significantly larger/higher than those in non-HIPs. HIPs were immunopositive for CD68 (11/11), glycophorin A (10/11), and fibrin (11/11). Glycophorin-A-, matrix metalloprotease 9 (MMP9)-, and tissue factor-immunopositive areas were larger in HIPs than in non-HIPs. The PMR was positively correlated with glycophorin-A-, fibrin-, MMP9-, and tissue factor-immunopositive areas. Blood coagulation shortened the T1 relaxation time of the blood and plasma, and the T1 relaxation times in coagulated whole blood and erythrocyte-rich blood were significantly shorter than those in plasma. Coronary HIPs may reflect intraplaque hemorrhage and may be a novel marker for plaque instability and thrombogenic potential.

Evaluation of the accuracy of mono-energetic electron and beta-emitting isotope dose-point kernels using particle and heavy ion transport code system: PHITS.

We assessed the accuracy of mono-energetic electron and beta-emitting isotope dose-point kernels (DPKs) calculated using the particle and heavy ion transport code system (PHITS) for patient-specific dosimetry in targeted radionuclide treatment (TRT) and compared our data with published data. All mono-energetic and beta-emitting isotope DPKs calculated using PHITS, both in water and compact bone, were in good agreement with those in literature using other MC codes. PHITS provided reliable mono-energetic electron and beta-emitting isotope scaled DPKs for patient-specific dosimetry.

Application of fiber tractography and diffusion tensor imaging to evaluate spinal cord diseases in dogs.

Fiber tractography is a technique capable of depicting the three-dimensional structure and connectivity of nerve fibers using serial magnetic resonance diffusion tensor imaging (DTI). To establish fiber tractography and DTI methods in veterinary clinical medicine, we evaluated fiber tractography and DTI parameters: apparent diffusion coefficient (ADC) values and fractional anisotropy (FA) values, in various spinal cord diseases. Spinal cord DTI was examined in 28 dogs with spinal cord diseases. The ADC and FA values were measured at lesion sites and cranial normal sites on spinal cords, and both values of lesion sites were compared with normal sites. In thoracolumbar intervertebral disk herniation (IVDH) cases, depending on their neurologic grades, fiber tractography indicated rupture of fiber trajectories, loss of neuronal bundles and disorder of fiber directions. In these cases, the average ADC values at lesion sites significantly decreased compared with normal sites (P=0.016). In the progressive myelomalacia case, the average ADC and FA values of hyperintense swollen regions in T2WI decreased compared to both values in other disease cases. Finally, in the meningioma case, the continuity of fiber trajectories improved after the administration of an anticancer agent. This study suggests that fiber tractography and DTI are useful in the diagnosis and prognosis of veterinary spinal cord diseases.

The agreement of left ventricular function parameters between (99m)Tc-tetrofosmin gated myocardial SPECT and gated myocardial MRI.

OBJECTIVE: The aim is to compare and evaluate the agreement of quantification of left ventricular functional parameters obtained by two different methods, (99m)Tc-tetrofosmin gated myocardial perfusion SPECT (MPS) and cardiac magnetic resonance imaging (CMR). METHODS: Ten healthy male volunteers participated. Gated MPS data were acquired using 32 frames, which were also combined into 16- and 8-frame data set for the investigation. Gated CMR data were acquired using 8, 16 and 32-frame for the different sets. All examinations were conducted in resting and at exercise conditions. Quantitative measurements of end-diastolic volume (EDV), end-systolic volume (ESV), left ventricular ejection fraction (LVEF), peak ejection rate (PER), peak filling rate (PFR) and time to peak filling (TTPF) were done for each study, respectively. Finally, we evaluated the concordance of parameters between gated MPS and gated CMR by % difference and Bland-Altman plot analysis. RESULTS: LVEF showed favorable concordance in both rest and exercise conditions (% differences were around 10%). PER, PFR and TTPF also showed good concordances in rest conditions, under 32-frame gated collections particularly (% differences were around 10%). In exercise conditions, although the concordances were relatively good, certain variances were noted (% differences were around 20-25%). Regarding left ventricular volumes, the concordance were worse in both conditions (% differences were around 30-40%). CONCLUSIONS: In quantifying of left ventricular function parameter, gated CMR provides similar quantitative values comparing with gated MPS except for ventricular volumes in rest conditions. In contrast, there were certain variations except for LVEF in exercised examinations. When we follow patients by the same cardiac parameters with CMR and MPS, using parameters across the two modalities proved to be possible under rest condition. However, it is limited at exercise condition.

MR signal change in venous thrombus relates organizing process and thrombolytic response in rabbit.

Venous thrombus is subsequently organized and replaced by fibrous connective tissue. However, the sequential changes in venous thrombi are not reliably detected by current noninvasive diagnostic techniques. The purpose of this study is to reveal whether magnetic resonance (MR) can detect venous thrombus, define thrombus age and predict thrombolytic responses. Thrombus in the rabbit jugular vein was imaged with a 1.5-T MR system at 4 h and at 1, 2 and 4 weeks using three-dimensional (3D) fast asymmetric spin echo T2-weighted (T2W) and 3D-gradient echo T1-weighted (T1W) sequences. The jugular veins were histologically assessed at each time point. Magnetic resonance imaging (MRI) was also performed in vivo before and 30 min after tissue plasminogen activator (t-PA) administration. The thrombi in MRI were comparable in size to histological sections. The signal intensity (SI) of thrombi at 4 h was heterogeneously high or low on T2W or T1W images, respectively. The SI of thrombi on T2W images decreased time-dependently, but increased on T1W images at 1 and 2 weeks. Morphological analysis showed time-dependent decreases in erythrocyte, platelet and fibrin areas and time-dependent increases in smooth muscle cell, macrophage, collagen and iron areas. The t-PA administration significantly decreased thrombus volume at 4 h but not at 1, 2 and 4 weeks. Venous thrombosis can be reliably and noninvasively detected by MRI. Measurement of SI might support assessments of thrombus age and thrombolytic response.

Cardiac rupture in acute myocardial infarction: post-mortem MR imaging.

We assessed acute myocardial infarction (AMI) with cardiac rupture in an autopsy using magnetic resonance (MR) imaging in vitro and histological staining. Cardiac MR imaging in vitro generated high resolution images of myocardial thinning, rupture, and epicardial hemorrhage. High signal intensity (SI) on T(1) weighted images (WI) and low SI on T(2)WI of the rupture site corresponded with acute myocardial necrosis, edema, and hemorrhage. A rupture site rich in erythrocytes after AMI might affect SI on T(1) and T(2)WI in cardiac MR imaging.

Atherosclerotic lesions rich in macrophages or smooth muscle cells discriminated in rabbit iliac arteries based on T1 relaxation time and lipid content.

RATIONALE AND OBJECTIVES: Atherothrombosis usually occurs on macrophage- and lipid-rich unstable plaque, but rarely on smooth muscle cell (SMC)-rich stable plaque. Magnetic resonance imaging (MRI) has been extensively applied for noninvasive vascular imaging. We therefore investigated whether MRI provides valuable information about the characteristics of atherosclerotic vessels using rabbit models of macrophage-rich or SMC-rich atherosclerotic arteries. MATERIALS AND METHODS: Rabbits were fed with a conventional (CD group, n = 3) or 0.5% cholesterol (ChD group, n = 3) diet for 1 week before and 3 weeks after balloon injury of the left iliac arteries. Three weeks later, these arteries were investigates by 1.5 T MRI and by conventional angiographic imaging, followed by histological and immunohistochemical analyses. RESULTS: Three weeks after balloon injury, injured iliac arteries of both groups formed neointima with luminal stenosis. Conventional and MRI angiographic findings of the luminal diameter significantly and positively correlated. T1 relaxation time was significantly shorter and the lipid content was much higher in injured arteries from the ChD than from the CD group. The injured arteries from the ChD also contained more macrophages and less SMCs that those from the CD group. The T1 relaxation time and lipid content in injured arteries negatively and positively correlated with the degree of macrophage accumulation, respectively. CONCLUSION: These results showed that MRI could provide valuable information about luminal stenosis and the characteristics of atherosclerotic vessels in rabbits.