Perfusion Curves Research Articles

Evaluation of dermal and subdermal microcirculation in free flaps with contrast harmonic ultrasound and indocyanine-green fluorescence video angiography

Purpose: Contrast harmonic ultrasound (CHI) with a linear transducer is a new diagnostic approach that allows dynamic and quantitative flow detection of tissue perfusion in microsurgery. The aim of the study was the evaluation of perfusion of the dermal and subdermal layers of microvascular tissue transplants with CHI in comparison to ICG-fluorescence angiography. Materials and methods: In a prospective clinical study Indocyanine-Green Fluorescence Video Angiography and Contrast Enhanced High Resolution Ultrasound (5–10MHz; linear transducer; Logiq 9; GE) were used for evaluation of the microcirculation in 10 transplanted free parascapular flaps. Two regions were analysed, the centre of the flap and the region of the anastomosis. The perfusion patterns of both methods were compared. Results: The perfusion indexes measured by ICG-fluorescence angiography correlated very precisely in all patients with the quantitative perfusion curves of contrast-enhanced US with CHI.Two flaps with slow filling and low dye intensity showed low contrast enhancement in CHI with modified perfusion curves with slow increase. In two cases a reduced perfusion and filling were found. There were no statistical differences between the two diagnostic methods (p>0.01). Conclusion: CHI improves US detections of dermal and subdermal microcirculation in comparison to ICG fluorescence angiography. CHI is a new diagnostic method for postoperative monitoring of free flaps.

Benign and Malignant Breast Lesions: Efficacy of Real Time Contrast-Enhanced Ultrasound vs. Magnetic Resonance Imaging

To assess the efficacy of low mechanical index (MI) real time grey scale contrast-enhanced US (CEUS) in the differentiation of breast lesions in comparison to Magnetic Resonance Imaging (MRI). 50 lesions previously detected at mammography or conventional US were evaluated by means of CEUS and MRI. Contrast-enhanced examinations were performed with a dedicated equipment (Esatune, Esaote, Genoa, Italy), before and after injection of 4.8 ml of Sonovue (Bracco, Milan, Italy). MRI was conducted with a 1.5 T equipment (Siemens Vision Plus, Erlangen, Germany) with bilateral dedicated superficial coil, on T2w STIR and 3D Flash T1w before and 1, 2, 3, 4, 5 minutes after the administration of contrast agent (Gd-DTPA, 1.5 ml/kg). Wash-in and wash-out curves were assessed for both procedures. A specific sonographic quantification software (Qontrast, Bracco, Milan, Italy), based on pixel by pixel signal intensity over time, was used to obtain contrast-enhanced sonographic perfusion maps for each lesion. Mc Nemar test was then calculated. 24 invasive ductal carcinomas, 18 fibroadenomas, 4 fibro-cystic dysplasias, 1 mucinous carcinoma, 1 invasive ducto-lobular carcinoma, 1 intraductal florid papillomatosis and 1 phylloides tumour were diagnosed. Contrast-enhanced sonographic patterns correlated well with those provided by MRI. Sensitivity, specificity, and accuracy of US were: 69.2 %, 66.7 %, and 68 %, respectively. According to the different contrast enhancement patterns and the resulting perfusion maps, all the malignant lesions and 9 out of 12 benign lesions were correctly diagnosed, thus resulting in 87.5 % of specificity and 100 % of sensitivity. Regarding the specificity, there is no difference between US and CEUS with McNemar (p = 0.18). Regarding sensitivity, the difference between contrast-enhanced US and US is significant as calculated with McNemar test (p = 0.013). The three lesions which were incorrectly classified as malignant were two hypervascularised fibroadenomas in young women and a phylloides tumour. CEUS seems to be a reliable method to differentiate breast lesions, since it provides typical enhancement patterns. Contrast sonographic perfusion curves correlate well with MRI wash in--wash out curves.

Assessment of hemodynamics in precancerous lesion of hepatocellular carcinoma: Evaluation with MR perfusion

To investigate the hemodynamic changes in a precancerous lesion model of hepatocellular carcinoma (HCC). Hemodynamic changes in 18 Wistar rats were studied with non-invasive magnetic resonance (MR) perfusion. The changes induced by diethylnitrosamine (DEN) developed into liver nodular lesions due to hepatic cirrhosis during the progression of carcinogenesis. The MR perfusion data [positive enhancement integral (PEI)] were compared between the nodular lesions corresponding well with MR images and pathology and their surrounding hepatic parenchyma. A total of 46 nodules were located by MR imaging and autopsy, including 22 dysplastic nodules (DN), 9 regenerative nodules (RN), 10 early HCCs and 5 overt HCCs. Among the 22 DNs, 6 were low-grade DN (LGDN) and 16 were high-grade DN (HGDN). The average PEI of RN, DN, early and overt HCC was 205.67 +/- 31.17, 161.94 +/- 20.74, 226.09 +/- 34.83, 491.86 +/- 44.61 respectively, and their liver parenchyma nearby was 204.84 +/- 70.19. Comparison of the blood perfusion index between each RN and its surrounding hepatic parenchyma showed no statistically significant difference (P = 0.06). There were significant differences in DN (P = 0.02). During the late hepatic arterial phase, the perfusion curve in DN declined. DN had an iso-signal intensity at the early hepatic arterial phase and a low signal intensity at the portal venous phase. Of the 10 early HCCs, 4 demonstrated less blood perfusion and 6 displayed minimally increased blood flow compared to the surrounding parenchyma. Five HCCs showed significantly increased blood supply compared to the surrounding parenchyma (P = 0.02). Non-invasive MR perfusion can detect changes in blood supply of precancerous lesions.

Preliminary application of MR perfusion-weighted imaging in the benign and malignant prostate diseases

目的 探讨MR灌注成像在前列腺良恶性病变中的初步应用,评价血管内皮生长因子(VEGF)和微血管密度(MVD)与MR灌注成像各指标的关系.方法对临床诊断为前列腺疾病的70例患者,其中良性前列腺增生(BPH)42例,前列腺癌(PCa)28例,进行MR灌注成像,并对标本进行免疫组织化学检测;分析病变的灌注曲线最大线性斜率(SSmax)、T2*弛豫率(△R2* peak)与免疫组织化学检查结果(VEGF、MVD)的相关性.结果(1)BPH组增生结节灌注曲线的SSmax及△R2* peak分别为:33.5±3.1、1.5±0.1;PCa组癌灶灌注曲线的SSmax及△R2* peak分别为:58.4±4.7、3.1±0.5,两者之间差异有统计学意义(t值分别为2.13、2.29,P值均＜0.05);PCa组高、中、低分化腺癌的SSmax分别为:52.3±3.4、56.4±4.3、60.7±5.2,差异有统计学意义(F=132.04,P＜0.05),△R2* peak分别为:2.9±0.4、3.1±0.5、3.2±0.7,差异有统计学意义(F=114.82,P＜0.05).(2)BPH组VEGF阳性9例,MVD值为22.76±6.54;PCa组VEGF阳性为24例,MVD值为71.38±9.17;PCa的VEGF和MVD的表达水平明显高于BPH患者(x2=27.86,P＜0.01;t=20.4,P＜0.01),PCa、BPH的VEGF表达与MVD表达呈正相关性(P＜0.01);灌注加权成像(PWI)参数SSmax、△R2* peak与VEGF、MVD具有相关性(P＜0.01).结论PWI的有关指标(SSmax、△R2* peak)与MVD和VEGF的表达水平相关,有可能为前列腺疾病良恶性的鉴别提供信息。

An automated image-processing strategy to analyze dynamic arterial spin labeling perfusion studies. Application to human skeletal muscle under stress

Arterial spin labeling (ASL) perfusion measurements allow the follow-up of muscle perfusion with high temporal resolution during a stress test. Automated image processing is proposed to estimate perfusion maps from ASL images. It is based on two successive analyses: at first, automated rejection of the image pairs between which a large displacement is detected is performed, followed by factor analysis of the dynamic data and cluster analysis to classify pixels with large signal variation characteristic of vessels. Then, after masking these "vascular" pixels, factor analysis and cluster analysis are further applied to separate the different muscles between low or high perfusion increase, yielding a functional map of the leg. Data from 10 subjects (five normal volunteers and five elite sportsmen) had been analyzed. Resulting time perfusion curves from a region of interest (ROI) in active muscles show a good accordance whether extracted with automated processing or with manual processing. This method of functional segmentation allows automated suppression of vessels and fast visualization of muscles with high, medium or low perfusion, without any a priori knowledge.

Solitary pulmonary nodules: Association between signal characteristics in dynamic contrast enhanced MRI and tumor angiogenesis

To estimate the association between signal characteristic of dynamic enhanced MRI using curve types and angiogenesis in solitary pulmonary nodules. Thirty-six patients with a solitary pulmonary nodule (SPN) ranging in size from 6 to 37 mm (median 17 mm) underwent dynamic contrast enhanced MRI with a time interval of 10 s over a total period of 4 min. Resulting from the time-intensity curves four different enhancement curve profiles (A-D) were defined: type A with strong increase followed by early washout, type B with strong increase without washout, type C with slow increase and type D without relevant increase. Maximum peak (Pmax), slope of the first bolus transit (slope) and washout were calculated. Microvessel densities (MVD) were counted at the margins and at the center of the nodules. The mean MVD of each nodule was calculated. Enhancement characteristics were correlated with MVD grouped by diagnosis and by curve types. Curve types were correlated with the score of vascular endothelial growth factor (VEGF). The frequency of malignancy was 55% (20/36). Using curve types for differentiation between malignant and benign SPN, the sensitivity, specificity and accuracy were 100%, 75% and 89%, respectively. The correlation between Pmax and MVD(mean) for all nodules was moderate (r(s)=0.4, P=0.02). A relevant correlation was found between Pmax and MVD(margin) in curve type A (r(s)=0.63; P=0.04) and Pmax and MVD(mean) in curve type C (r(s)=0.86; P=0.006). No positive correlation was found between Pmax and MVD (mean, center and margin) in curve type B. No significant correlation was found for slope and washout. VEGF score correlated positively with curve types (r(s)=0.67; P<0.001). A relevant association between perfusion curve profiles and angiogenesis was found in malignant nodules having early washout and in benign lesion with a slow increase of enhancement. In cases of strong signal increase without washout additional factors for enhancement must be considered. The use of curve profiles could allow for the estimation of the extent of VEGF.

Comparison of Tc-99m DTPA and Tc-99m MAG3 Perfusion Time-Activity Curves in Patients With Renal Allograft Dysfunction

Aim The perfusion time-activity curve on DTPA renal scintigraphy shows a peak and plateau pattern which is usually absent or less marked when using tubular agents such as MAG3. The exact mechanism that results in this difference between the two tracers is not well understood. A descending pattern on MAG3 has been proposed to be due to decreased extraction. In this study we compared the diagnostic utility of perfusion patterns obtained with DTPA and MAG3 among patients with renal allograft dysfunction. Materials and methods This study included 48 patients with renal allograft dysfunction and 18 recipients with normal graft function. Every recipient had renal scintigraphy with Tc-99m MAG3 and Tc-99m DTPA 1 day apart. The second phase of the perfusion curve after the initial rise was classified as ascending, flat, or descending. In patients with a descending curve on DTPA study, we calculated the ratio of counts at peak perfusion to that at plateau (P:PL). Impaired perfusion was based on a deterioration of the peak-to-plateau pattern on DTPA and the presence of a flat-descending curve on MAG3. Results In patients with dysfunction, impaired perfusion was observed in 77% of DTPA and in 54% of MAG3 studies. A flat-descending curve on MAG3 was present in 44% of patients with normal graft function. By MAG3, 67% of acute rejection and 28% of chronic allograft nephropathy (CAN) cases showed deteriorated perfusion. The corresponding values for DTPA were 67% and 94%, respectively. A flat-ascending pattern on DTPA was more frequent in CAN than it was in acute rejection (33% and 17%, respectively). Conclusion The sensitivity of DTPA perfusion pattern for diagnosing dysfunction was significantly greater than that for MAG3. Our results suggest that the major determinant of a curve pattern on DTPA or MAG3 study is the extraction relative to perfusion. Thus for patients with CAN, extraction is higher relative to perfusion, resulting in a lower P:PL ratio or an ascending curve on DTPA. Although the extraction of DTPA is less than that of MAG3, this level of extraction renders DTPA more sensitive to serial changes in renal function and pathophysiological mechanisms related to kidney function.

Promising techniques for breast cancer detection, diagnosis, and staging using non-ionizing radiation imaging techniques

Traditional imaging for the diagnosis and staging of breast cancer has relied on the tissue morphology of cancers in the background of normal patterns of fibroglandular breast tissue. X-ray mammography and ultrasound have been the primary modalities for the diagnosis and the work-up of breast cancer. New modalities have been validated including magnetic resonance imaging (MRI) and positron emission tomography (PET). New pulse sequences in MRI combined with contrast enhancement kinetic perfusion curves have greatly enhanced detection of mammographically occult cancers. New modalities on the horizon include optical imaging, exploiting again the differential perfusion properties of cancers in a background of normal glandular tissue. Even more specificity can be ach eved with the addition of ductal or intravenous introduction of optical probes specific to tumor associated antigens such as the HER-2/neu receptor in aggressive breast cancers. Quantum dots and other fluorescent dyes coupled to peptides or other probes will greatly enhance our ability to detect cancers earlier and without ionizing radiation.

Single-Session Magnetic Resonance Coronary Angiography and Myocardial Perfusion Imaging Using the New Blood Pool Compound B-22956 (Gadocoletic Acid)

The objective of this study was to evaluate a new blood pool contrast agent, B-22956, for detecting myocardial perfusion abnormality and coronary artery stenosis by magnetic resonance imaging (MRI) in 1 setting. Coronary artery atherosclerotic stenoses were created in 6 miniswine. Myocardial first-pass perfusion imaging was performed with a bolus injection of 0.015 mmol/kg B-22956 during pharmacologic stress followed by postcontrast coronary artery imaging after another injection of B-22956/1. The total doses for the 6 pigs were 0.1 mmol/kg (n=3) and 0.15 mmol/kg (n=3). Perfusion upslope maps were analyzed and MR coronary artery images were reviewed by 2 readers. For all 6 pigs, the normalized upslopes of the perfusion curves were 0.83+/-0.12, 0.74+/-0.15, and 0.52+/-0.05 (P<0.01 vs. normal) with normal or mild (<50% area stenosis), moderate (<50% and <75%), and severe stenosis (>75%), respectively. Mean signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) in right coronary artery images improved 90% and 200%, respectively, with a total dose of 0.1 mmol/kg of B-22956. Excellent agreements (kappa=0.82) were achieved for evaluating the grade of stenosis between MR postcontrast coronary artery images and histopathology by 2 reviewers. The MR blood pool contrast agent B-22956 demonstrated the ability for detecting myocardial perfusion abnormalities and coronary artery stenosis in 1 setting.

Clinical Use of Renal Perfusion Imaging by Means of Harmonic Sonography With a Microbubble Contrast Agent in Patients After Renal Transplantation

The purpose of this research was to determine the feasibility of renal perfusion imaging by means of harmonic sonography with a microbubble contrast agent for the evaluation of renal perfusion after renal transplantation compared with technetium Tc 99m diethylenetriamine pentaacetic acid ((99m)Tc-DTPA) scans. During a 10-month period, 100 patients with renal transplantation that included normal perfusion (n=68) and delayed perfusion including chronic rejection (n=19), acute rejection (n=9), arterial stenosis (n=2), and urinary stricture (n=2) underwent sonographic renal perfusion imaging and (99m)Tc-DTPA scans. Sonographic images were obtained every 3 seconds for a total of 3 minutes after administration of a bolus injection of 4 g of the microbubble contrast agent at a concentration of 300 mg/mL. Sonographic renal perfusion images were converted into a renal perfusion curve, and the calculated time at the peak of the curve (T(peak)) was compared with that of the (99m)Tc-DTPA scan. The T(peak) with the (99m)Tc-DTPA scan was 14.9 seconds in the normal group and 33 seconds in the delayed perfusion group. The T(peak) on sonographic renal perfusion images was 25 seconds in the normal group and 44.8 seconds in the delayed perfusion group. Sonographic renal perfusion images showed good correlation with the (99m)Tc-DTPA scan (r=0.74; P=.0001). The cutoff value of the T(peak) on sonographic renal perfusion images was 35 seconds (sensitivity=85%; specificity=90%). The renal perfusion images obtained by means of harmonic sonography with a microbubble contrast agent constitute an effective sonographic technique for the evaluation of renal perfusion abnormalities after renal transplantation compared with a (99m)Tc-DTPA scan.

Perfusion abnormalities in congenital and neoplastic pulmonary disease: comparison of MR perfusion and multislice CT imaging

The aim of this work was to assess magnetic resonance (MR) perfusion patterns of chronic, non-embolic pulmonary diseases of congenital and neoplastic origin and to compare the findings with results obtained with pulmonary, contrast-enhanced multislice computed tomography (CT) imaging to prove that congenital and neoplastic pulmonary conditions require MR imaging over the pulmonary perfusion cycle to successfully and directly detect changes in lung perfusion patterns. Twenty-five patients underwent concurrent CT and MR evaluation of chronic pulmonary diseases of congenital (n=15) or neoplastic (n=10) origin. Analysis of MR perfusion and contrast-enhanced CT datasets was realized by defining pulmonary and vascular regions of interest in corresponding positions. MR perfusion calculated time-to-peak enhancement, maximal enhancement and the area under the perfusion curve. CT datasets provided pulmonary signal-to-noise ratio measurements. Vessel center-lines of bronchial arteries were determined. Underlying perfusion type, such as pulmonary arterial or systemic arterial supply, as well as regions with significant variations in perfusion were determined statistically. Analysis of the pulmonary perfusion pattern detected pulmonary arterial supply in 19 patients; six patients showed systemic arterial supply. In pulmonary arterial perfusion, MR and multislice CT imaging consistently detected the perfusion type and regions with altered perfusion patterns. In bronchial arterial supply, MR perfusion and CT imaging showed significant perfusion differences. Patients with bronchial arterial supply had bronchial arteries ranging from 2.0 to 3.6 mm compared with submillimeter diameters in pulmonary arterial perfusion. Dynamic MR imaging of congenital and neoplastic pulmonary conditions allowed characterization of the pulmonary perfusion type. CT imaging suggested the presence of systemic arterial perfusion by visualizing hypertrophied bronchial arteries.

Automatic detection of renal rejection after kidney transplantation

Acute rejection is the most important reason of graft failure after kidney transplantation, and early detection is crucial to survive the kidney function. Dynamic Contrast Enhanced Magnetic Resonance Imaging (DCE-MRI) is an imaging modality where a contrast agent (such as Gd-DTPA) is introduced into the kidney and rapid and repeated images are taken, which allows both the anatomic and functional information of the kidney to be monitored. Using these images, this paper introduces an accurate method for the segmentation of the kidney from the surrounding structures by introducing a shape model of the kidney into the external energy component of the deformable models. Secondly, registration algorithms are employed to account for the motion of the kidney due to patient breathing and finally, the perfusion curves obtained from the cortex that show the transportation of the contrast agent into the tissue are given for future classification of normal and acute rejection transplants. Applications of the proposed algorithms yield promising results.

Hepatic Perfusion and Hemodynamic Effects of Transjugular Intrahepatic Portosystemic Shunts

The liver depends on a dual blood supply from the hepatic artery and the portal vein. The normal liver receives 70% portal flow and 30% hepatic arterial flow, with most arterial blood feeding the biliary tree. As cirrhosis robs the liver of its regenerative capacity, the portal flow decreases and intrahepatic portosystemic shunting increases with a variable increase in arterial flow across arterioportal shunts. This compensation mechanism attempts to reperfuse remaining sinusoids. Transjugular intrahepatic portosystemic shunts (TIPS) or surgical portosystemic shunts may acutely diminish portal perfusion further, leading to hepatic failure. Small-diameter TIPS or surgical shunts reduce the incidence of complications by preserving nutritive portal flow. Although the inverse relationship of arterial and portal flow is physiologically valid, there is individual variation in the ability to substitute one blood supply for another. This variability may result from anatomic or functional factors influencing the flow across arterioportal shunts. Hepatic perfusion curves derived from enhanced imaging studies can subtype cirrhotic patients into favorable versus unfavorable perfusion patterns. Patients with high arterial flow to the liver or patients with retained portal-type flow curves have better survival and morbidity compared with those patients with unfavorable flow manifest by diminished arterial-type curves on hepatic perfusion analysis.

Hepatic Perfusion as a Predictor of Mortality after Transjugular Intrahepatic Portosystemic Shunt Creation in Patients with Refractory Ascites

To determine whether hepatic perfusion patterns predict mortality after transjugular intrahepatic portosystemic shunt (TIPS) creation in patients with severe ascites. This retrospective study included 22 patients who had enhanced cine magnetic resonance (MR) imaging performed immediately before TIPS creation in the angled coronal plane including the left kidney, liver, and main portal vein. Regions of interest were centered over the liver and kidney, and perfusion curves were generated and reviewed before the standard TIPS procedure was performed. Four patients did not undergo TIPS creation as a result of very poor hepatic perfusion by MR. All patients were followed clinically and by ultrasound surveillance of their shunt. Eleven patients died within 6 months, including all four patients who did not have a TIPS because of MR evidence of poor hepatic perfusion. Of these 11 patients, eight (73%) had unfavorable liver flow consisting of diminished enhancement compared to the kidney and early peak enhancement of less than 50 seconds. The surviving patients all showed a delayed peak enhancement of greater than 50 seconds. In patients undergoing TIPS creation for refractory ascites, blunted arterial-type hepatic enhancement is a poor prognostic sign. Cine MR imaging with evaluation of hepatic perfusion can be performed and reviewed before the TIPS procedure. Alternative techniques for ascites reduction may be preferred for patients with unfavorable hepatic perfusion.

Renal Perfusion Image Using Harmonic Ultrasound with Microbble Contrast Agent: Preliminary Study

Purpose: To compare, in terms of their feasibility and normal range, Tc-DTPA renal perfusion imaging and renal perfusion imaging using harmonic ultrasound (US)with a microbubble contrast agent for the evaluation of renal perfusion after renal transplantation. Materials and Methods: During a six-month period, thirty patients who had received a renal transplant underwent both Tc-DTPA renal perfusion imaging and renal perfusion imaging using harmonic US with a microbubble contrast agent. Sonographic renal perfusion images were obtained before and after a bolus injection of the microbubble contrast agent Levovist (SH U 508A; Schering AG, Berlin, Germany) every 3 seconds for 3 minutes. Sonographic renal perfusion images were converted into a renal perfusion curve by a computer program and Tpeak of the curve thus obtained was compared with that of the Tc-DTPA curve. Results: Average T of the Tc-DTPA renal perfusion curve was 16.2 seconds in the normal group and 39.6 seconds in the delayed perfusion group, while average T of the sonographic renal perfusion curve was 23.7 seconds and 46.2 seconds, respectively. T of the sonographic renal perfusion curve showed a good correlation with that of the Tc-DTPA curve (correlation coefficient=0.8209; p=0.0001). The cut-off value of T of the sonographic renal perfusion curve was 35 seconds (sensitivity=90%, specificity=95%). Conclusion: In patients who have received a renal transplant, the findings of renal perfusion imaging using harmonic US with a microbubble contrast agent show close correlation with those of Tc-DTPA renal perfusion imaging. The optimal cut-off value of Tpeak of the sonographic renal perfusion curve was 35 seconds

Surveillance postopératoire des lambeaux libres osseux de péroné ou fibula par IRM dynamique. Résultats préliminaires à propos de trois cas en reconstruction mandibulaire

Postoperative monitoring of vascularized free fibular grafts by dynamic contrast-enhanced MRI. A preliminary report on three cases of mandibular reconstruction. The vascularized free fibular graft has been used in mandibular reconstructive surgery since 1975. This technique has been progressively developed, and it is now the procedure of choice for mandibular reconstruction although in certain postoperative circumstances it can be difficult if not impossible to monitor bone vitality. However, bone vascularization can be detected by dynamic magnetic resonance imaging (MRI), as this technique has been experimentally and clinically validated in the early diagnosis of osteonecrosis. The aim of this study was to evaluate the efficacy of MRI for the postoperative monitoring of vascularized free fibular grafts in human mandibular reconstruction. Dynamic contrast-enhanced MRI was used to study the variation in contrast over time following injection of gadolinium contrast medium, and to evaluate the degree of bone marrow perfusion of the fibular graft. This variation in signal intensity was visualized in the form of a curve, i.e., a perfusion curve for the bone marrow region. An examination was performed in three patients at different postoperative times and under different conditions. In one case, MRI confirmed the presence of fibula blood supply in spite of the necrosis of the adjacent fascio-adipose layer. In this article, the methodological difficulties have been discussed, particularly as regards data processing, and the present results have been compared with the findings in the literature. Dynamic MRI is a simple, reliable, non-invasive technique and its use in the postoperative monitoring of bone marrow perfusion and vascularized free fibular grafts permits a determination of the status of the latter following surgery, i.e., whether there is an adequate blood supply or not.

Pitfalls in myocardial perfusion assessment with dynamic MR imaging after administration of a contrast material bolus in dogs

The authors evaluated the artifacts observed on myocardial perfusion curves derived from an inversion-prepared fast gradient-echo (GRE) imaging sequence in dogs after injection of a gadolinium-based contrast agent. Six mongrel dogs were divided into three groups. In groups 1 and 2, anesthesia was maintained with pentobarbital. Group 2 also received an intravenous injection of atropine (0.03 mg/kg). In group 3, anesthesia was maintained with isoflurane (1.0%). Imaging was performed on a 1.5-T magnetic resonance (MR) imaging unit (one section per heart beat, a 30 x 15-cm field of view, 10-mm section thickness, and 64-kHz bandwidth). Region-of-interest (ROI) markers were placed on the blood pool of the left intraventricular cavity, anterior wall of the left ventricle, and anterior to the chest wall to track respiratory motion. In group 1, the signal intensity (SI) periodically increased during each inspiration due to respiratory sinus arrhythmia. The relation between the SI increase and the variation of the delay between images was demonstrated in vitro and by computer simulations. No periodic increase of the SI was observed when regular cardiac rhythm was maintained by pharmacologic inhibition of the vagal-mediated chronotropic response with either the addition of atropine to pentobarbital or the use of isoflurane as the anesthetic agent. In an inversion-prepared fast GRE sequence, respiratory sinus arrhythmia can induce periodic SI increase by varying the respiratory rate interval and delay between images.

Quantification of myocardial perfusion with FAST sequence and Gd bolus in patients with normal cardiac function.

The present study reports on a new calibration of the magnetic resonance imaging (MRI) signal intensity of a fast gradient-echo sequence used for in vivo myocardial perfusion quantification in patients. The signal from a FAST sequence preceded by a arrhythmia-insensitive magnetization preparation was calibrated in vitro using tubes filled with various gadolinium (Gd) solutions. Single short-axis views of the heart were obtained in patients (n = 10) with normal cardiac function. Myocardial and blood signal intensity were converted to concentration of Gd according to the in vitro calibration curve and fitted by a one-compartment model. K1 [first-order transfer constant from the blood to the myocardium for the gadolinium-diethylenetriamine-pentaacetic acid (Gd-DTPA)] and Vd (distribution volume of Gd-DTPA in myocardium) obtained from the fit of the MRI-derived perfusion curves were 0.72+/-0.22 (mL/min/g) and 15.3+/-5.22%. These results were in agreement with previous observations on animals and demonstrated that a reliable measurement of myocardial perfusion can be obtained by MRI in patients with an in vitro calibration procedure.

Endothelium‐dependent vasodilation of the skin microcirculation in heart transplant recipients

Patients with heart failure demonstrate attenuated endothelium‐dependent vasodilation of the peripheral circulation, while this is suggested to be reversed after heart transplantation. However, data from human subjects are limited and conflict with studies on the peripheral vasomotor tone in cyclosporine‐treated animals, suggesting endothelial dysfunction. We recorded forearm skin perfusion responses following graded iontophoresis of 1% acetylcholine (endothelium‐dependent) and 1% sodium nitroprusside (endothelium‐independent) by laser Doppler perfusion measurements in 32 heart transplant recipients and 15 age‐matched controls. In addition, the hyperemic response to 3 min of blood flow occlusion to the forearm was measured on the third finger pulp. With comparable baseline values, the increases in perfusion to the 4 applications of acetylcholine were significantly attenuated in heart transplant recipients compared with controls: 599 vs. 146±32, 24239 vs. 492 ± 77, 480 ± 66 vs. 845 ± 120 and 699 ± 77 vs. 993 ± 139% (mean ± SEM; all p &lt;0.01). Peak hyperemia (134±4 vs. 153 ± 12 arbitrary units (AU); p&lt;0.05)), time for the hyperemic perfusion to return to preocclusive baseline (52.4 vs. 102.9 s; p &lt; 0.01) and hence the area under the perfusion curve (1469±244 vs. 4581±921 AU s; p&lt;0.01) were reduced among heart transplant recipients. The area under the perfusion curve correlated significantly with mean arterial blood pressure (r = ‐0.60; p &lt; 0.01) and with the responses to iontophoresis of acetylcholine (r = 0.41; p&lt;0.01). Two non‐invasive tests of vascular function demonstrate attenuated endothelial‐dependent microvascular responses in heart transplant recipients. The relative impact. of prior congestive heart failure and postoperative factors, such as treatment with cyclosporine, remains to be determined.

Significance of early tubular extraction in the first minute of Tc-99m MAG3 renal transplant scintigraphy.

Renal transplant perfusion curves obtained using Tc-99m MAG3 differ from those with Tc-99m DTPA. The perfusion curve can be divided into a first phase (up to the first-pass peak) and a second phase (the curve after the initial peak). The second phase of the MAG3 perfusion curve is usually ascending in contrast to the descending Tc-99m DTPA curve. This ascending MAG3 curve reflects early tubular extraction of MAG3. However, the second phase of the MAG3 curve is sometimes flat or descending. We hypothesized that a flat or descending curve reflects poor early tubular extraction and therefore graft dysfunction. Ninety-two studies of 59' renal transplant patients were retrospectively reviewed. The second phase of the perfusion curve was visually classified as ascending, flat, or descending. 77.2% of studies had ascending curves, 16.3% flat curves, and 6.5% descending curves. A descending curve had a positive predictive value (PPV) of 100% for medical graft dysfunction, while a flat curve had a PPV of 93.3%. A nonascending second phase curve was specific (96.4%) but not sensitive (33.9%) for graft dysfunction. Patients with acute tubular necrosis were not significantly more likely to have a nonascending curve than those with acute rejection. There was no significant difference in creatinine level between patients with medical graft dysfunction and ascending vs. nonascending curves. A nonascending second phase Tc-99m MAG3 perfusion curve is predictive for graft dysfunction. An ascending curve is nonspecific and can be seen in both normally and poorly functioning grafts.