Phantom-Based Standardization Method for 123I-metaiodobenzylguanidine Heart-to-Mediastinum Ratio Validated by D-SPECT Versus Anger Camera.

Background: The 123I-metaiodobenzylguanidine heart-to-mediastinum ratios (HMRs) have been standardized between D-SPECT and Anger cameras in a small patient cohort using a phantom-based conversion method. This study aimed to determine the validity of this method and compare the diagnostic performance of the two cameras in a larger patient cohort. Methods: We retrospectively calculated HMRs from early and late anterior-planar equivalent and planar images acquired from 173 patients in 177 studies using D-SPECT and Anger cameras, respectively. The D-SPECT HMRs were cross-calibrated to an Anger camera using conversion coefficients based on previous phantom findings, then standardized to medium-energy general-purpose collimator conditions. Relationships between HMRs before and after corrections were investigated. Late HMRs were classified into four cardiac mortality risk groups and divided into two groups using a threshold of 2.2 to verify diagnostic performance concordance. Results: Correction improved linear regression lines and differences in HMRs among the groups. The overall ratios of perfect concordance were (134 [75.7%] of 177), and higher in groups with very low (49 [80.3%] of 61) and high (51 [86.4%] of 59) HMRs when the standardized HMR was classified according to cardiac mortality risk. That between the systems was the highest (164 [92.7%] of 177) when the HMR was divided by a threshold value of 2.2. Conclusions: Phantom-based conversion can standardize HMRs between D-SPECT and Anger cameras because the standardized HMR provided comparable diagnostic performance. Our findings indicated that this conversion could be applied to multicenter studies that include both D-SPECT and Anger cameras.

Cross calibration of 123I-meta-iodobenzylguanidine heart-to-mediastinum ratio with D-SPECT planogram and Anger camera.

BACKGROUND: Cardiac 123I-meta-iodobenzylguanidine (MIBG) uptake is quantified using the heart-to-mediastinum ratio (HMR) with an Anger camera. The relationship between HMR determined using D-SPECT with a cadmium-zinc-telluride detector and an Anger camera is not fully understood. Therefore, the present study aimed to define this relationship using images derived from a phantom and from patients. METHODS: Cross-calibration phantom studies using an Anger camera with a low-energy high-resolution (LEHR) collimator and D-SPECT, and clinical 123I-MIBG studies proceeded in 40 consecutive patients (80 studies). In the phantom study, a conversion coefficient (CC) was defined based on phantom experiments and applied to the Anger camera and the D-SPECT detector. The HMR was calculated using anterior images with the Anger camera and anterior planograms with D-SPECT. First, the HMR from D-SPECT was cross-calibrated to the Anger camera, and then, the HMR from both cameras were converted to the medium-energy general-purpose collimator condition (CC 0.88; ME88 condition). The relationship between HMR and corrected and uncorrected methods was examined. A 123I-MIBG washout rate was calculated using both methods with and without background subtraction. RESULTS: Based on the phantom experiments, the CC of the Anger camera with an LEHR collimator and of D-SPECT using an anterior planogram was 0.55 and 0.63, respectively. The original HMR from the Anger camera and D-SPECT was 1.76 ± 0.42 and 1.86 ± 0.55, respectively (p < 0.0001). After D-SPECT HMR was converted to the Anger camera condition, the corrected D-SPECT HMR became comparable to the values under the Anger camera condition (1.75 ± 0.48, p = n. s.). When the HMR measured using the two cameras were converted under the ME88 condition, the average standardized HMR from the Anger camera and D-SPECT became comparable (2.21 ± 0.65 vs. 2.20 ± 0.75, p = n. s.). After standardization to the ME88 condition, a systematic difference in the linear regression lines disappeared, and the HMR from both the Anger (StdHMRAnger) and D-SPECT (StdHMRDSPECT) became comparable. Additional correction using a regression line further improved the relationship between both HMR [StdHMRDSPECT = 0.09 + 0.98 × StdHMRAnger (R 2 = 0.91)]. The washout rate closely correlated with and without background correction between both methods (R 2 = 0.83 and 0.65, respectively). CONCLUSION: The phantom-based conversion method is applicable to D-SPECT and enables the common application of HMR irrespective of D-SPECT and the Anger camera.

Importance of Defect Detectability in Positron Emission Tomography Imaging of Abdominal Lesions.

OBJECTIVES: This study was designed to assess defect detectability in positron emission tomography (PET) imaging of abdominal lesions. METHODS: A National Electrical Manufactures Association International Electrotechnical Commission phantom was used. The simulated abdominal lesion was scanned for 10 min using dynamic list-mode acquisition method. Images, acquired with scan duration of 1-10 min, were reconstructed using VUE point HD and a 4.7 mm full-width at half-maximum (FWHM) Gaussian filter. Iteration-subset combinations of 2-16 and 2-32 were used. Visual and physical analyses were performed using the acquired images. To sequentially evaluate defect detectability in clinical settings, we examined two middle-aged male subjects. One had a liver cyst (approximately 10 mm in diameter) and the other suffered from pancreatic cancer with an inner defect region (approximately 9 mm in diameter). RESULTS: In the phantom study, at least 6 and 3 min acquisition durations were required to visualize 10 and 13 mm defect spheres, respectively. On the other hand, spheres with diameters ≥17 mm could be detected even if the acquisition duration was only 1 min. The visual scores were significantly correlated with background (BG) variability. In clinical settings, the liver cyst could be slightly visualized with an acquisition duration of 6 min, although image quality was suboptimal. For pancreatic cancer, the acquisition duration of 3 min was insufficient to clearly describe the defect region. CONCLUSION: The improvement of BG variability is the most important factor for enhancing lesion detection. Our clinical scan duration (3 min/bed) may not be suitable for the detection of small lesions or accurate tumor delineation since an acquisition duration of at least 6 min is required to visualize 10 mm lesions, regardless of reconstruction parameters. Improvements in defect detectability are important for radiation treatment planning and accurate PET-based diagnosis.

Ventilatory impairment detection based on distribution of respiratory-induced changes in pixel values in dynamic chest radiography: a feasibility study.

PURPOSE: Decreased ventilation is observed on chest radiographs as small changes in X-ray translucency, and ventilatory impairments can therefore be detected by analyzing the distribution of respiratory-induced changes in pixel value. This study was performed to develop a ventilatory impairment detection method based on the distribution of respiratory-induced changes in pixel values. METHODS: Sequential chest radiographs during respiration were obtained using a dynamic flat panel detector system. Respiratory-induced changes in pixel value were measured in each local area and then compared for symmetrical positions in both lungs, which were located at the same distance from the axis of the thorax at the same level. The right-left symmetry was assessed in 20 clinical cases (Abnormal, 14; Normal, 6). RESULTS: In normal controls, the distribution was symmetrical, and there were good correlations of the pixel value changes in both lungs at symmetrical positions (r = 0.66 ± 0.05). In contrast, abnormal cases did not show a symmetrical distribution of pixel value changes (r = 0.40 ± 0.23) due to ventilation abnormalities observed as reductions in pixel value changes. CONCLUSIONS: Ventilatory impairment could be detected as deviation from the right-left symmetry of respiratory-induced changes in pixel value. In particular, the present method could be useful for detecting unilateral abnormalities. However, to detect bilateral abnormalities, further studies are required to develop multilevel detection methods combined with several methods of pattern analysis.

Development of pulmonary blood flow evaluation method with a dynamic flat-panel detector: quantitative correlation analysis with findings on perfusion scan.

Pulmonary blood flow is reflected in dynamic chest radiographs as changes in X-ray translucency, i.e., pixel values. Thus, decreased blood flow should be observed as a reduction of the variation of X-ray translucency. We performed the present study to investigate the feasibility of pulmonary blood flow evaluation with a dynamic flat-panel detector (FPD). Sequential chest radiographs of 14 subjects were obtained with a dynamic FPD system. The changes in pixel value in each local area were measured and mapped on the original image by use of a gray scale in which small and large changes were shown in white and black, respectively. The resulting images were compared to the findings in perfusion scans. The cross-correlation coefficients of the changes in pixel value and radioactivity counts in each local area were also computed. In all patients, pulmonary blood flow disorder was indicated as a reduction of changes in pixel values on the mapping image, and a correlation was observed between the distribution of changes in pixel value and those in radioactivity counts (0.7

Pulmonary blood flow evaluation using a dynamic flat-panel detector: feasibility study with pulmonary diseases.

PURPOSE: Pulmonary ventilation and circulation dynamics are reflected on fluoroscopic images as changes in X-ray translucency. The purpose of this study was to investigate the feasibility of non-contrast functional imaging using a dynamic flat-panel detector (FPD). METHODS: Dynamic chest radiographs of 20 subjects (abnormal, n = 12; normal, n = 8) were obtained using the FPD system. Image analysis was performed to get qualitative perfusion mapping image; first, focal pixel value was defined. Second, lung area was determined and pulmonary hilar areas were eliminated. Third, one cardiac cycle was determined in each of the cases. Finally, total changes in pixel values during one cardiac cycle were calculated and their distributions were visualized with mapping on the original image. They were compared with the findings of lung perfusion scintigraphy. RESULTS: In all normal controls, the total changes in pixel value in one cardiac cycle decreased from the hilar region to the peripheral region of the lung with left-right symmetric distribution. In contrast, in many abnormal cases, pulmonary blood flow disorder was indicated as a reduction of changes in pixel values on a mapping image. The findings of mapping image coincided with those of lung perfusion scintigraphy. CONCLUSIONS: Dynamic chest radiography using an FPD system with computer analysis is expected to be a new type of functional imaging, which provides pulmonary blood flow distribution additionally.

[Pulmonary functional diagnostic imaging using a dynamic flat-panel detector: comparison with findings in pulmonary scintigraphy].

Pulmonary ventilation and circulation dynamics are reflected on dynamic chest radiographs as changes in X-ray translucency,i.e., pixel values. The present study was performed to develop a pulmonary functional evaluation method based on the changes in pixel value, and to investigate the clinical usefulness of our method. Sequential chest radiographs of 20 subjects (abnormal,n=12; normal,n=8) during respiration were obtained with a dynamic flat-panel detector (FPD) system. The average pixel value in each local area was measured tracking the same area. To facilitate visual evaluation, the results were mapped on the original image using a grayscale in which small changes were shown in black and large changes were shown in white. In our clinical evaluation in comparison with a pulmonary scintigraphy, pulmonary ventilation disorder was indicated as a reduction of changes in pixel values. In many patients, there was a correlation between our result and a pulmonary scintigraphy (0.7

A change of in vivo characteristics depending on specific activity of radioiodinated (+)-2-[4-(4-iodophenyl)piperidino]cyclohexanol [(+)-pIV] as a ligand for sigma receptor imaging.

The radioiodinated (+)-p-iodovesamicol [(+)-pIV], which shows a high binding affinity for sigma-1 (sigma-1) receptors, is prepared by an exchange reaction. The specific activity (SA) is fairly low and therefore is insufficient for clinical use. In this study, we prepared (+)-[(125)I]pIV with a high SA from tributylstannyl precursor and compared the in vivo characteristics between high and low SA by imaging sigma-1 receptors in the central nervous system. In the biodistribution study, a difference in brain accumulation was observed between the two methods. At 30 min postinjection, the brain accumulation (1.58%ID/g) of low SA [0.6-1.1 TBq/mmol (16-30 Ci/mmol)] (+)-[(125)I]pIV was higher than that (1.34%ID/g) of high SA [>88.8 TBq/mmol (>2400 Ci/mmol)] (+)-[(125)I]pIV. In the blocking study, the brain uptake of high SA (+)-[(125)I]pIV was reduced more significantly by the coadministration of sigma ligands such as pentazocine, haloperidol or SA4503 than that of low SA (+)-[(125)I]pIV. These results showed that nonspecific binding of high SA (+)-[(125)I]pIV in the brain was lower than that of low SA (+)-[(125)I]pIV, and high SA (+)-[(125)I]pIV bound more specifically to sigma-1 receptors in the brain than low SA (+)-[(125)I]pIV. In contrast, in the blood-binding study, high SA (+)-[(125)I]pIV (58.4%) bound to blood cells with higher affinity than low SA (+)-[(125)I]pIV (46.0%). In metabolite studies, blood metabolites of high SA (+)-[(125)I]pIV (57.3+/-3.5%) were higher than those of low SA (+)-[(125)I]pIV (45.5+/-4.1%) at 30 min postinjection. Higher SA may be apt to bind to blood cells with higher affinity and to be metabolized faster.

Magnesium attenuates isoproterenol-induced acute cardiac dysfunction and beta-adrenergic desensitization.

Sympathetic nervous activation is a crucial compensatory mechanism in heart failure. However, excess catecholamine may induce cardiac dysfunction and beta-adrenergic desensitization. Although magnesium is known to be a cardioprotective agent, its beneficial effects on acute cardiac dysfunction remain to be elucidated. We examined the effects of magnesium on left ventricular (LV) dysfunction induced by a large dose of isoproterenol in dogs. Sixteen anesthetized dogs underwent a continuous infusion of isoproterenol (1 micro g.kg(-1).min(-1)) with or without a magnesium infusion (1 mg.kg(-1).min(-1)). The dose response to small doses of isoproterenol (0.025-0.2 micro g.kg(-1).min(-1)) was tested hourly. A large dose of isoproterenol decreased LV systolic function, increased the time constant of LV isovolumic relaxation, and suppressed the dose response to small doses of isoproterenol in a time-dependent manner. Magnesium significantly attenuated isoproterenol-induced LV systolic and diastolic dysfunction and preserved the dose response to isoproterenol. Serum-ionized calcium significantly decreased with a large dose of isoproterenol but was fully maintained at baseline level with magnesium. A large dose of isoproterenol increased serum lipid peroxide levels and serological markers of myocardial damage, which were significantly suppressed by magnesium. In conclusion, magnesium significantly attenuated excess isoproterenol-induced acute cardiac dysfunction and beta-adrenergic desensitization.

Renal artery stenosis emerged after angiotensin-converting enzyme inhibitor treatment for myocardial infarction: a case report.

A 76-year-old woman with acute myocardial infarction underwent percutaneous coronary angioplasty followed by treatment with an angiotensin-converting enzyme (ACE) inhibitor, lisinopril. Her renal function deteriorated after the administration of lisinopril, so it was changed to another ACE inhibitor, temocapril. Renography suggested a complication of severe right renal artery stenosis, and renal angiography revealed bilateral renal artery stenoses. Her renal hemodynamics were assessed by (99m)Tc-Mercaptoacetyltriglycine ((99m)Tc-MAG(3))-renography before and after withdrawal of temocapril. The authors concluded the patient had essential hypertension complicated by atherosclerotic renovascular disease. In the treatment of elderly patients with heart disease, hypertension, or both, with ACE inhibitor, the possibility of coexisting renal artery stenosis should be considered. Renography is recommended as a reliable tool for detecting renal artery stenosis.

Unequal effects of renin-angiotensin system inhibitors in acute cardiac dysfunction induced by isoproterenol.

Several clinical trials have demonstrated that angiotensin-converting enzyme inhibitor (ACEI) and angiotensin II type 1 receptor blocker (ARB) are equally effective in the treatment of chronic heart failure. However, this has not been confirmed for acute cardiac dysfunction. We examined whether ACEI or ARB prevents isoproterenol-induced acute left ventricular (LV) dysfunction in dogs. LV dysfunction induced by a large dose of isoproterenol (1 microg.kg(-1).min(-1), 3-h infusion) was compared in dogs treated with ACEI (temocaprilat) or ARB (olmesartan). Atrial pacing induced a constant heart rate and use of adjustable aortic banding provided a nearly constant afterload. LV systolic function (LV dP/dt, fractional shortening, and ejection fraction) and diastolic function (tau and LV end-diastolic pressure) were significantly deteriorated after isoproterenol infusion. The LV dysfunction was almost totally prevented by ARB but was only partially prevented by ACEI. The partial effect of ACEI was complemented by cotreatment with HOE-140, a bradykinin B2 receptor antagonist. At baseline, the response to low doses of isoproterenol was significantly attenuated by ACEI but not by ARB, and the ACEI-induced attenuation was totally abolished by cotreatment with HOE-140. The response to isoproterenol was significantly attenuated after 3 h of excess isoproterenol loading, and it was almost completely preserved by ARB but not by ACEI. In conclusion, acute LV dysfunction and beta-adrenergic desensitization induced by excess isoproterenol administration were almost totally prevented by ARB but only partially prevented by ACEI. These differences were attributable at least in part to bradykinin pathways activated by ACEI administration in acute LV dysfunction.

Changes in regional cerebral blood flow in irradiated regions and normal brain after stereotactic radiosurgery.

OBJECTIVE: To elucidate the radiation effect on the normal brain after stereotactic radiosurgery (SRS), we evaluated the change in regional cerebral blood flow (CBF) in targeted and extra-targeted areas according to the radiation dose given. METHODS: Thirteen patients who underwent SRS for brain tumors or arteriovenous malformations were included in this study. Maximum radiation doses to the lesion ranged from 24 to 37 Gy. Mean and regional CBF were measured by 99mTc-HMPAO scintigraphy with graphic analysis, performed at before, 2 weeks and 3 months (5 patients) after SRS. Under the co-registration with the CT with superimposed isodose distribution, ROIs were set on target (37-20 Gy), peri-target (20-5 Gy) and out-of-field (5-2 Gy and less than 2 Gy) areas on the quantitative SPECT images. RESULTS: Significant reductions in mean CBF (by 7%) and regional CBF in the peri-target areas (by 5-7%) and out-of-field areas (by 6-22%) were recognized at 2 weeks and 3 months after SRS. Regional CBF in the target and peri-target areas did not significantly change, presumably because there was little or no normal tissue in these areas. CONCLUSION: These results suggest that subclinical regional CBF reduction occurs after SRS in the normal brain in out-of-field of radiation.