Dynamic MR imaging of liver metastases with Gd-EOB-DTPA

Purpose: To assess liver and lesion enhancements by dynamic MR imaging after bolus injection of the hepatobiliary contrast agent gadolinium ethoxybenzyldiethylenetriamine-pentaacetic acid (Gd-EOB-DTPA) in patients with liver metastases and to compare the effect of different doses.Material and Methods: A randomized double-blinded trial with doses of 12.5, 25 and 50 μmol/kg Gd-EOB-DTPA was performed in 35 patients with liver metastases. Liver enhancement, tumor enhancement and liver lesion contrast-to-noise (C/N) ratios were calculated from breath-hold gradient echo images (100/5/80°) recorded precontrast and at different times up to 10 min postcontrast.Results: Normal liver showed a characteristic enhancement pattern, with a rapid enhancement in the first 45 s postcontrast and a slight but significant further increase up to 600 s. The initial enhancement in the lesions was also pronounced, but the enhancement was slightly decreased after 240 s postcontrast. At dose levels of 12.5 and 25 μmol/kg Gd-EOB-DTPA, C/N ratios significantly increased compared to baseline from 90 to 600 s. Postcontrast C/N-values obtained using 50 μmol/kg Gd-EOB-DTPA were not significantly increased, except for the examinations 480 s postcontrast.Conclusion: In liver metastases, C/N ratios obtained with doses of 12.5 and 25 μmol/kg Gd-EOB-DTPA were slightly superior to 50 μmol/kg Gd-EOB-DTPA. This finding is probably due to a more pronounced extracellular effect of the contrast medium at higher doses.     

Cardiac metal contents after infusions of manganese. An experimental evaluation in the isolated rat heart.

RATIONALE AND OBJECTIVES: Manganese dipyridoxyl diphosphate (MnDPDP), a contrast agent for liver MRI, releases free Mn2+ in a graded manner. The aim of the study was to compare the effects of brief versus prolonged infusions of MnDPDP and manganese chloride (MnCl2) on cardiac function, metabolism, Mn accumulation, and tissue metal content. METHODS: Isolated perfused rat hearts received 1-minute or 10-minute infusions of MnDPDP (100 microM, 1000 microM) or of MnCl2 (10 microM, 100 microM). Physiologic indices were measured intermittently, and tissue high-energy phosphate compounds and Ca/Fe/Mg/Mn/Zn contents were measured after a standardized Mn washout. RESULTS: One-minute and 10-minute infusions induced, respectively, minor and marked depressions of contractile function and corresponding elevations in myocardial Mn content. MnCl2 was markedly more potent than MnDPDP. Ten-minute infusions of the highest concentration of MnDPDP and MnCl2 lowered tissue Mg and elevated tissue Ca (MnCl2), whereas high-energy phosphates were unaffected. CONCLUSIONS: Mn uptake after Mn infusion is strongly related to the duration, concentration, and dose of free Mn ions. Differences in Mn accumulation between MnDPDP and MnCl2 were more pronounced after the 10-minute infusion.     

Development of an automated system for the quick production of N-labeled compounds with high specific activity using anhydrous [N]NH3

An automated system was developed to synthesize ¹³N-labeled compounds with high specific activity using anhydrous [¹³N]NH₃ as a synthetic precursor. This system enabled (1) production of an aqueous solution of [¹³N]NH₃, (2) concentration and desiccation of the [¹³N]NH₃ solution, (3) reaction of anhydrous [¹³N]NH₃ with substrate, (4) purification and formulation.

By the use of this system, [¹³N]p-nitrophenyl carbamate ([¹³N]NPC) ready for i.v. injection could be obtained in 5.1±0.1 min at the yield of 3.5±0.4 GBq, specific activity 460±55 GBq/μmol, and radiochemical purity >99% (n=3) by irradiating a 10 mM ethanol solution with 18 MeV protons at 17 μA for 25 min. With special precautions, [¹³N]NPC could be obtained at the extremely high specific activity of 1800±200 GBq/μmol.     

Percutaneous transhepatic portal vein embolization: effectiveness of absolute ethanol infusion with balloon catheter in a pig model

Purpose: To evaluate the effectiveness of portal vein embolization (PVE) with absolute ethanol using multidetector-row computed tomography (CT) angiography in a pig model.

Material and Methods: Percutaneous transhepatic PVE with 10 ml absolute ethanol was performed in liver segments (n = 5) or subsegments (n = 5) in 10 pigs. CT images and volumetric data were qualitatively and quantitatively assessed to determine future liver remnant (FLR) hypertrophy and to correlate with histopathologic changes 2-6 weeks after PVE. Effectiveness evaluation was based on changes in absolute FLR size and ratio of FLR to total estimated liver volume (TELV).

Results: Occlusion of the embolized vessel was achieved immediately after injecting absolute ethanol within a range of 0.25-0.33 ml/kg. The TELV prior to PVE was 660.49±103.66 cm³ (range 527.22 to 833.70 cm³) and after PVE 769.51±29.36 cm³ (range 685.95 to 887.34 cm³). The mean FLR/TELV ratio increase after PVE was 14.2%. No statistically significant difference was found in the increase of TELV between segmental or subsegmental PVE. On microscopic observation, atrophy of the embolized liver was noted in all animals and was seen distinctly at 3 weeks after PVE in 2 animals.

Conclusion: Both regenerative response and histopathologic changes of the liver were seen after PVE with absolute ethanol with a mean FLR/TELV ratio of 14.2%.     

Manganese dipyridoxyl diphosphate (MnDPDP)-enhanced magnetic resonance imaging of acute reperfused myocardial injury in a cat model: part I: comparison with pathologic examination

RATIONALE AND OBJECTIVES: To investigate the capacity of manganese dipyridoxyl diphosphate (MnDPDP)-enhanced magnetic resonance imaging (MRI) to discriminate the injured myocardium from the normal myocardium in a cat model. MATERIALS AND METHODS: Fourteen cats were prepared for acute myocardial infarction with 90-minute occlusion followed by 120-minute reperfusion. Inversion recovery gradient-recalled echo (IR-GRE) MR images were obtained at 60-minute intervals for 4 hours after the injection of MnDPDP, and ex vivo after the cats were killed. We evaluated the differences between the unenhanced area on the in vivo and ex vivo MR images and the unstained area on triphenyl tetrazolium chloride (TTC) staining. RESULTS: The unenhanced area on the in vivo MR images was well correlated with that on the ex vivo MR images. The unenhanced area on the ex vivo MR images was significantly larger than the unstained area on TTC staining. CONCLUSIONS: This study suggests that the MnDPDP-unenhanced area on the MR images includes not only the infarcted myocardium but also the stunned myocardium.     

Manganese dipyridoxyl diphosphate. Effect of dose, time, and pulse sequence on hepatic enhancement in rats

We used an animal model to investigate the hepatic enhancement characteristics of manganese dipyridoxyl diphosphate (MnDPDP) related to time, dose, and pulse sequence. The contrast doses selected were in the human tolerance range. Using an SE 300/15 pulse sequence, maximum mean hepatic enhancement of 45% (8 mumols/kg) and 58% (12 mumols/kg) over baseline was seen during a plateau maintained between 5 and 50 minutes postinjection in the 8 mumols/kg group, and between 10 and 90 minutes in the 12 mumols/kg group. This plateau was followed by a very gradual decline in hepatic enhancement. Using either 4 or 8 mumols/kg, there was a significant increase in postcontrast hepatic intensity on all relatively T1-weighted pulse sequences (spin echo [SE] 300/15, inversion recovery [IR] 1400/20/400, gradient echo [GE] 47/13/80 degrees, and GE 60/20/30 degrees) except GE 47/13/80 degrees at 4 mumols/kg. At 8 mumols/kg there was superior enhancement, with IR 1400/20/400 and SE 300/15, but at 4 mumols/kg there was no consistently superior sequence. None of the relatively T2-weighted pulse sequences (SE 2000/50, SE 2000/100, or GE 100/30/20 degrees) demonstrated a significant change in hepatic intensity using either dose of contrast. The data suggest that the best combination of dose, pulse sequence, and time for hepatic imaging with MnDPDP is 8 mumols/kg using heavily T1-weighted sequences 5 to 60 minutes following contrast administration.     

Effects of methoxyflurane anesthesia on the pharmacokinetics of I-IAZA in sprague–dawley rats

Effects of methoxyflurane anesthesia on the pharmacokinetics of intravenous ¹²⁵I-IAZA in rats are reported. No significant differences in t_1/2, t_1/2β, V_ss, and Cl_TB for total radioactivity (¹²⁵I-IAZA and metabolites) were observed between the anesthetized (Group 1, n = 4) and nonanesthetized (Group 2, n = 3) animals. For ¹²⁵I-IAZA, Cl_TB increased from 646 ± 52 mL/h/kg to 2250 ± 351 mL/h/kg and t_1/2β decreased from 97.7 ± 17.5 min to 35.6 ± 5.4 min, for Groups 1 and 2, respectively. There were no differences in V_ss or t_1/2 between the two groups. These findings support literature reports of anesthetic effects on xenobiotic pharmacokinetics, and indicate a need for caution in the evaluation of preclinical imaging studies in which animals are immobilized with anesthetics.     

Dynamic evaluation of the hepatic uptake and clearance of manganese-based MRI contrast agents: A 31P NMR study on the isolated and perfused rat liver

This spectroscopic study compares the mechanisms of the hepatic uptake of manganese chloride (MnCl₂) and manganese dipyridoxyl diphosphate (MnDPDP). Alterations of the phosphorus-31 (³¹P)-NMR spectrum of the intracellular adenosine 5′-triphosphate (ATP) are used to monitor the internalization of manganese by the isolated and perfused rat liver. Mn²⁺ delivered as MnCl₂ in the perfusate rapidly enters the hepatocytes, where it strongly interacts with ATP, inducing a broadening of the ³¹P lines. The inhibition of the process by nifedipine confirms that manganese ions cross the cellular membrane at least partly through Ca²⁺ channels. MnDPDP induces weaker but still significant changes of the ATP spectrum. The inability of pyridoxine to compete for the uptake of manganese confirms that the vitamin B₆ carrier is not involved in the internalization process of the paramagnetic complex. Finally, preincubation of MnDPDP with blood does not increase the extent of the dissociation. The alterations of the ³¹P spectrum of the liver subsequent to the administration of MnDPDP are attributable to a fraction of free Mn²⁺ released by the chelate and delivered to the hepatocytes.     

SPECT imaging of myocardial infarction using 99mTc-labeled C2A domain of synaptotagmin I in a porcine ischemia-reperfusion model

INTRODUCTION: The C2A domain of synaptotagmin I recognizes necrotic and apoptotic cells by binding to exposed anionic phospholipids. The goal is to explore the potential imaging utility of 99mTc-labeled C2A in the detection of acute cardiac cell death in a porcine model that resembles human cardiovascular physiology. METHODS: Ischemia (20-25 min) was induced in pigs (M/F, 20-25 kg) using balloon angioplasty. 99mTc-C2A-GST (n=7) or 99mTc-BSA (n=2) was injected intravenously 1-2 h after reperfusion. Noninfarct animals were injected with 99mTc-C2A-GST (n=4). SPECT images were acquired at 3 and 6 h postinjection. Cardiac tissues were analyzed to confirm the presence of cell death. RESULTS: Focal uptake was detected in five out of seven subjects at 3 h and in all infarct subjects at 6 h postinjection but not in infarct animals injected with 99mTc-BSA or in noninfarct animals with 99mTc-C2A-GST. Gamma counting of infarct versus normal myocardium yielded a 10.2+/-5.7-fold elevation in absolute radioactivity, with histologically confirmed infarction. CONCLUSIONS: We present data on imaging myocardial cell death in the acute phase of infarction in pigs. C2A holds promise and warrants further development as an infarct-avid molecular probe.     

Adeno-associated viral vector-encoding vascular endothelial growth factor gene: effect on cardiovascular MR perfusion and infarct resorption measurements in swine

PURPOSE: To prospectively determine in swine the effects of cardiac-specific and hypoxia-inducible vascular endothelial growth factor (VEGF) expression gene on angiogenesis and arteriogenesis by using cardiovascular magnetic resonance (MR) imaging for evaluation of infarct resorption and left ventricular (LV) function. MATERIALS AND METHODS: The investigation conformed to U.S. National Institutes of Health guidelines. Twelve pigs with reperfused infarcts were studied with cardiovascular MR 3 days and 8 weeks after surgery. In six pigs, adeno-associated viral (AAV) vector-encoding VEGF (AAV-VEGF) gene was injected at eight sites 1 hour after reperfusion. Six pigs served as controls. Cardiovascular MR measurements of perfusion, area at risk, infarct size, and LV function were used in evaluation of the therapy. Hematoxylin-eosin, Masson trichrome, and biotinylated isolectin B4 stains were used to assess regional vascular density. Two-way Student t test was used to determine significant differences between means. RESULTS: AAV-VEGF had no effect on cardiovascular MR perfusion or infarct size measurements 3 days after infarction. At 8 weeks, the therapy increased infarct resorption, perfusion, and vascular density and prevented deterioration of ejection fraction in treated animals. These changes were associated with a significantly greater reduction in extent of enhanced region in treated (18.6% of LV surface area +/- 1.5 [standard error of mean] to 9.8% +/- 1.1) than in control animals (17.7% +/- 1.8 to 14.5% +/- 1.5, P = .028). Histopathologic findings in treated animals showed increased capillary and arterial density in infarct and periinfarct regions. These new vessels were active and thin-walled compared with thick-walled vessels of control animals. CONCLUSION: AAV-VEGF improves cardiovascular MR measurement of regional myocardial perfusion and LV function.     

Assessment of infarct size by positron emission tomography and [18F]2-fluoro-2-deoxy-D-glucose: a new absolute threshold technique

Along with hibernating myocardium, infarct size is a critical term in the progression of left ventricular remodelling and congestive heart failure. Both infarcted and hibernating myocardium determine changes in remote non-ischaemic tissue. This study was designed to test the accuracy of a new technique to quantify infarct size using positron emission tomography (PET) with [18F]2-fluoro-2-deoxy-D-glucose (FDG). Studies were carried out in (a) nine pigs with acute myocardial infarction (two sham-operated), produced by a 90-min occlusion of the circumflex coronary artery followed by a 4-h reperfusion, and (b) humans (six patients with ischaemic cardiomyopathy awaiting cardiac transplantation and five normal volunteers). In both animals and patients, myocardial FDG uptake was measured by PET during hyperinsulinaemic-euglycaemic clamp. Infarct size was quantified by an absolute threshold of tracer uptake obtained from the parametric (voxel-by-voxel) image of the metabolic rate of FDG. PET infarct size estimates were compared with independent ex vivo planimetric measurements of the explanted swine and patient hearts (at transplantation) after staining with triphenyltetrazolium chloride. There was good agreement between the planimetric and PET infarct size estimates both in pigs (n=9; r=0.96, v=0.94x+0.64, SEE=0.10, P<0.0001) and in humans (n=11; r=0.94, y=0.72x+2.93, SEE=0.09, P<0.0001). This study demonstrates the feasibility and accuracy of this PET method in estimating infarct size both in a model of reperfused acute myocardial infarction and in chronic ischaemic cardiomyopathy, although larger studies are needed to confirm these findings.     

Efficient synthesis of 2-bromo-1-[F]fluoroethane and its application in the automated preparation of F-fluoroethylated compounds

An efficient synthesis of 2-bromo-1-[¹⁸F]fluoroethane from commercially available 1,2-dibromoethane and its integration into an automated preparation device was developed for the routine synthesis of ¹⁸F-fluoroethylated compounds. The 1,2-dibromoethane was reacted with the [¹⁸F]fluoride/Kryptofix^®2.2.2./carbonate complex in acetonitrile at 70°C for 3 min resulting in 60–70% radiochemical yields. The crude reaction mixture was diluted with water, loaded on a LiChrolute^®EN-cartridge, eluted with acetonitrile and passed through an AluminaB^®-cartridge. This method provides 2-bromo-1-[¹⁸F]fluoroethane with 98% radiochemical purity and <0.1 μmol of 1,2-dibromoethane within 10 min, thus avoiding a purifying distillation step. This method was easily integrated into an automated system for the routine synthesis of ¹⁸F-fluoroethylated compounds.     

Axon tracing in the adult rat optic nerve and tract after intravitreal injection of MnDPDP using a semiautomatic segmentation technique

PURPOSE: To develop and validate an objective technique for 3D segmentation of manganese-enhanced MR images of the optic nerve/tract (ON) in adult rats to improve contrast-to-noise (CNR) calculations and use the technique to ascertain if manganese dipyridoxyl diphosphate (MnDPDP) gives sufficient Mn(2+) enhancement compared to MnCl(2) when used for functional imaging of the visual pathway. MATERIALS AND METHODS: Intravitreous injection of the manganese-releasing MR contrast agent MnDPDP (30 nmol Mn(2+)) was performed to trace the ON in adult rats (n = 4). A positive control group of rats (n = 5) received a standard preparation of MnCl(2) (200 nmol Mn(2+)), while gadodiamide (1500 nmol Gd(3+)) was administered in negative control rats (n = 2). An objective technique for 3D segmentation of the enhanced ON was developed. CNR profiles along the ON were calculated by resampling the 3D image-volume in 2D planes perpendicular to the Mn(2+) enhanced ON in 0.2 mm steps, 4 mm along the segmented ON measured from the lamina cribrosa. RESULTS: The ON was successfully segmented and CNR calculated accurately within 2 minutes in a representative 3D MR image volume. Intravitreal MnDPDP injection resulted in significant MRI contrast enhancement of the retina and ON after 12-24 hours similar to that of MnCl(2) injection. CONCLUSION: 3D semiautomated image segmentation and the use of MnDPDP can improve in vivo axon tracing based on MRI. Mn(2+) was found to be released from MnDPDP after intravitreal injection in sufficient amounts to obtain functional tracing of the adult rat primary visual pathway.     

Manganese dipyridoxyl diphosphate (MnDPDP)-enhanced magnetic resonance imaging of acute reperfused myocardial injury in a cat model: part II: comparison with cine magnetic resonance imaging

RATIONALE AND OBJECTIVES: To compare manganese dipyridoxyl diphosphate (MnDPDP)-enhanced magnetic resonance imaging (MRI) with cine MRI for distinguishing the dysfunctional myocardium from the normal myocardium. MATERIALS AND METHODS: Seventeen cats were prepared for acute myocardial infarction with 90 minutes of occlusion followed by 120 minutes of reperfusion. In vivo inversion-recovery gradient-recalled echo MRI and cine MRI were performed. Two radiologists independently analyzed the MR images and recorded the size of the unenhanced area on the MnDPDP-enhanced MR images as well as that of the dysfunctional area on the cine MR images. Agreement between these abnormal areas was evaluated using Bland-Altman analysis. Interobserver agreement was assessed using Bland-Altman analysis. RESULTS: The sizes of the unenhanced area on the MnDPDP-enhanced MR images and the dysfunctional area on the cine MR images showed good agreement on Bland-Altman analysis (the limits of agreement: observer 1= 1.8% +/- 11.6, observer 2 = 0.1% +/- 9.9). The abnormal segments on both types of MR imaging showed a good interobserver agreement (the limits of agreement: MnDPDP-enhanced MRI = 0.3% +/- 7.6, cine MRI = -1.4% +/- 10.9). CONCLUSION: The size of the dysfunctional area on the cine MR images was well correlated with that of the unenhanced area on the MnDPDP-enhanced MR images.     

Detection of acute myocardial ischemia using first-pass dynamics of MnDPDP on inversion recovery echoplanar imaging

Previous studies used manganese N,N'-bis-(pyridoxal 5-phosphate)ethylenediamine-N,N'-diacetic acid (MnDPDP) to detect myocardial ischemia at a dose of 0.4 mmol/kg with spin echo imaging. The purpose of this study was to detect acute myocardial ischemia using MnDPDP at a dose range near that approved for hepatobiliary imaging (0.005 mmol/kg) in conjunction with inversion recovery echoplanar imaging (IR EPI). Regional ischemia was produced in 26 rats by occluding the left coronary artery for 20-30 minutes before imaging. Consecutive 32 IR EP images (inversion time [TI]/TR/TE 700/2000/10 msec) were obtained to monitor the first pass of MnDPDP at four incremental doses (0.005, 0.01, 0.02, or 0.04 mmol/kg, n = 6-8). MnDPDP produced dose-dependent enhancement of left ventricular blood and normal myocardium, but not ischemic myocardium. Quantitative analysis revealed a difference in signal intensities (P<0.05) between normal and ischemic myocardium at the time of peak enhancement in all groups. However, differential enhancement between normal and ischemic myocardium produced clear visual delineation of the ischemic region only at doses > or =0.01 mmol/kg. In conclusion, acute myocardial ischemia can be detected with IR EPI using doses close to the clinically approved dose of MnDPDP.     

藏红花酸抗心律失常作用研究

目的研究藏红花酸的抗实验性心律失常的作用机制。方法将实验动物随机分为生理盐水组,阳性药物对照组,藏红花酸高、中、低剂量组,SD大鼠采用1.2g/kg乌拉坦麻醉后,从尾静脉匀速(0.1ml/min)灌注10μg/ml乌头碱溶液,豚鼠麻醉后从颈静脉匀速(0.1ml/min)灌注9μg/ml哇巴因溶液,观察出现室性期前收缩(VE)、室性心动过速(VT)、室颤(VF)和心脏停搏的时间,然后换算成乌头碱和哇巴因的累积量;快速推注4%氯化钙(140mg/kg)诱导大鼠心律失常,观察给药后心律失常出现时间、持续时间、心律失常发生数及死亡数。结果与给予生理盐水比较,给予高、中、低剂量藏红花酸均能提高由乌头碱所致大鼠VE、VT、VF的用量,也能提高哇巴因所致豚鼠VE、VT、VF的用量,明显降低氯化钙诱导大鼠VE或VF的发生率及死亡率。结论藏红花酸有明显的抗大鼠心律失常作用,其抗心律失常作用可能与其抑制钠离子(Na+)内流或钙离子(Ca2+)内流等因素有关。     

Tumor uptake of radioiodinated anti-human pulmonary surfactant-associated protein monoclonal antibody PE10 in nude mice bearing human pulmonary adenocarcinoma in combination with an unlabeled preload

This study assessed the potential use of radioimmunoscintigraphy of pulmonary alveolar Type II cells tumor with the radiolabeled anti-human surfactant-associated protein (SP) monoclonal antibody (MAb) PE 10 in combination with preloads of unlabeled MAb. The in vitro binding of iodine-125 (¹²⁵I)-labeled MAb PE 10 (1 μg), which had a specific radioactivity of 400 MBq/mg, on human pulmonary papillary adenocarcinoma NCI-H441 cells that produced SP was investigated. In NCI-H441 tumor-bearing nude mice, the tumor uptake of ¹²⁵I-MAb PE 10 (5 μg) was examined in combination with preloads of unlabeled MAb PE 10 (0, 5, 10, and 50 μg). An isotype-matched unassociated murine MAb was used as a control both in vitro and in vivo. ¹²⁵I-MAb PE 10 showed specific cell binding compared with ¹²⁵I-control MAb. Tumor uptake of ¹²⁵I-MAb PE 10 in vivo reached a peak of 4.97±0.33% injected dose per gram (%ID/g) at 48 h postinjection. Preloads of 5 and 10 μg unlabeled MAb PE 10 significantly enhanced tumor uptake at 48 h postinjection ( 5.94±0.29% ID/g and 5.72±0.29% ID/g, respectively), whereas preload of 50 μg unlabeled MAb PE 10 significantly decreased tumor uptake ( 2.75±0.32% ID/g) at 48 h. Preload of 5 μg unlabeled MAb PE 10 significantly increased the tumor-to-blood radioactivity ratio at 48 h ( 2.39±0.16). Preloads of unlabeled control MAb did not cause any significant change in tumor uptake. Immunohistochemistry showed the intracellular and pericellular patterns of SP expression in tumor cells. In conclusion, radioimmunoscintigraphy with MAb PE 10 labeled with a γ-emitting radioiodine such as ¹²³I might be a useful means of targeting pulmonary alveolar Type II tumor cells in combination with preloading with an optimal dose of the unlabeled MAb.     

Evaluation of effective dose from a RANDO phantom in videofluorography diagnostic procedures for diagnosing dysphagia

Objectives

Videofluorography (VF) is useful for diagnosing dysphagia; however, few reports have investigated appropriate effective doses for VF. The present study aimed to estimate the effective radiation dose in VF for diagnosis of dysphagia.

Methods

Radiation doses to tissues and organs were measured using the anthropomorphic RANDO woman phantom as an equivalent to the human body. Effective doses were estimated according to the recommendations of the International Commission on Radiological Protection (ICRP) 60 in 1990 and IRCP 103 in 2007. The tissues measured were those recommended by ICRP 60 and ICRP 103 including gonads (ovaries and testes), red bone marrow and tissues in which excessive radiation commonly causes malignant tumours including lung, thyroid gland, stomach, large intestine, liver, oesophagus, bladder, breast, bone marrow, skin, brain and salivary gland. Skin dose was also measured using thermoluminescent dosimeters.

Results

Using ICRP 103, the effective dose was estimated as 118.1 μSv at a tube voltage of 50 kV and 82.4 μSv at 45 kV. However, using ICRP 60 the effective dose for 1 min of VF was estimated at 62.4 μSv and 47.2 μSv under the same exposure conditions.

Conclusions

Using ICRP 103, the effective dose for VF per examination at a total estimation time of 1 min was estimated as approximately 2.5–8.3 times that observed for digital panoramic radiography and 1/12 to 3 times depending on the measurement device for cone beam CT (CBCT). This value can be decreased in the future using a smaller irradiation field and decreased time for examination in VF in the future.     

Detection of liver metastases in colorectal cancer on chemotherapy. Comparative study between MRI with teslascan and computed tomography with intravenous contrast media

OBJECTIVE: To compare MRI of the liver with mangafodipir trisodium (MnDPDP) and computed tomography with intravenous contrast media in the follow-up of liver metastases in patient on chemotherapy for colorectal carcinoma. MATERIALS AND METHODS: This was a prospective study with patients on chemotherapy for liver metastases from colorectal cancer. Patients underwent both contrast-enhanced helical CT using 2 cc/kg contrast at 3 cc/sec and mangafodipir trisodium-enhanced MR imaging at 1.5 T using 2-3 cc/min contrast at 5 micro mol/kg within a two week interval. Two experienced radiologists independently reviewed all scans in a blinded fashion and recorded image quality as well as presence and number of liver lesions. Statistical analysis was performed using the wilcoxon signed rank test. RESULTS: All examinations were of good quality. A total of 71 lesions were detected at CT, with 69 lesions consistent with metastases and 2 lesions consistent with cysts. A total of 98 lesions were detected at MRI, with 97 consistent with metastases and 1 lesion consistent with a cyst. T1 weighted images with MnDPDP significantly detected two additional lesions compared to CT (p<0.05). No significant difference was demonstrated between T1 weighted images without MnDPDP and CT or between T2 weighted images and CT. CONCLUSION: Magnetic resonance imaging with MnDPDP is significantly more sensitive than unenhanced MRI and helical CT for the follow-up of liver lesions.     

Myocardial perfusion imaging with 99mTc sestamibi early after reperfusion reliably reflects infarct size reduction by ischaemic preconditioning in an experimental porcine model

OBJECTIVE: Reliable methods for assessment of tissue reperfusion early after revascularizing therapy for acute myocardial infarction are needed. Myocardial perfusion imaging with Tc sestamibi (MIBI MPI) may serve this purpose. Usage during early reperfusion may be problematic e.g. due to ischaemic preconditioning (IP), which is important in inducing ischaemic tolerance. It is mediated through the opening of mitochondrial K ATP channels, reducing mitochondrial membrane potential. This may, as well as ischaemia per se, affect cellular uptake of Tc sestamibi. We therefore studied the reliability of MIBI MPI during early reperfusion as a measure of infarct size and its reduction by ischaemic preconditioning. METHODS AND RESULTS: We compared MIBI MPI (cut-off, 45% of maximum pixel count) with a histochemical method in a porcine model, nine controls and eight IP pigs, using 45 min catheter based coronary occlusion of the left anterior descending artery. Infarct size (IS) was determined relative to the area at risk (AAR). The relative infarct size (IS/AAR) after 120 min reperfusion estimated by MPI was 0.83 (0.17) in controls vs 0.07 (0.12) in the IP group (mean (SD), P<0.001). The corresponding values for histochemistry were controls 0.77 (0.19) vs IP 0.07 (0.11), P<0.001. IS/AAR measured by MPI and histochemistry were correlated significantly (r=0.93, P<0.001). Furthermore, IS relative to left ventricular mass (IS/LV) determined by autoradiography and histochemistry correlated (r=0.93, P<0.001). MPI overestimated IS/LV and AAR/LV by approximately a factor of 2 compared with histochemistry or autoradiography. CONCLUSION: MIBI MPI during early reperfusion is a reliable measure of relative infarct size reduction after ischaemic preconditioning, supporting use for stratification for adjunctive therapy and for assessment of prognosis.