Comparison of breath-hold 2D phase-contrast with non breath-hold cine phase-contrast MRA in the assessment of azygos venous blood flow in portal hypertension

Azygos venous blood flow as an index of blood flow through the gastroesophageal collaterals and varices is of value in the prediction of gastrointestinal bleeding. Measurement of azygos venous blood flow has been achieved by non breath-hold (NBH) cine phase-contrast magnetic resonance imaging. The objective of this study was to compare the faster breath-hold (BH) phase-contrast technique with the standard (NBH) cine phase-contrast technique in the measurement of azygos blood flow. Thirty-two cirrhotic patients with esophageal varices were examined by magnetic resonance imaging using a BH technique and a NBH cine phase-contrast technique to measure the flow velocity, flow volume and calibre of the azygos vein at the mid-right atrial level. The flow values were obtained on the velocity image of the phase-contrast study. Values obtained from the two methods were evaluated statistically for the strength and significance of correlation by the Pearson test. Measurement by the BH method performed at full-inspiration as well as end-expiration was also obtained in 15 healthy volunteers. The breath-hold phase-contrast method has significant but weak correlation with non BH cine phase-contrast method in the measurement of azygos venous blood flow volume (r=0.55, p<0.01) and flow velocity (r=0.43, p=0.01). However, the calibre of the azygos vein gave a strong correlation in these two methods (0.82). In the subgroup of patients whose azygos blood flow velocity was greater than 7.4 cm/s, the correlation of azygos blood flow volume is strong (r=0.80, p<0.01). The azygos vein calibre remains highly correlated between the BH and NBH method, in both high flow velocity (r=0.73) and low flow velocity (r=0.83) groups. Breath-hold sequence leads to higher values for flow velocity and flow volume in the cirrhotic patients and also the control group. In patients with portal hypertension, BH 2D phase-contrast (PC) magnetic resonance angiography (MRA) could give a comparable estimation of the calibre of the azygos vein as the NBH 2D cine PC MRA but not for azygos flow volume. In patients with high azygos flow velocity, the strong correlation in flow volume between the BH and NBH method suggests that the BH method may be a time-saving alternative to the NBH method.     

Semi-quantitative approach to estimating GFR by magnetic resonance imaging

Objective: The purpose of this study was to compare a semi-quantitative approach to estimating glomerular filtration rate (GFR) by magnetic resonance imaging with radionuclide calculation of GFR, and to investigate whether spin echo or gradient echo is more suitable for estimating GFR.Methods and patients: Fourteen kidneys of seven patients (GFR ranging from 26 to 57 ml/min) were studied. Spin echo and gradient echo sequences interleaving each other at every excitation were used. After intravenous injection of gadopentetate dimeglumine, serial scans were performed. The signal intensities measured in the regions of interest were converted to time-transverse relaxation rate changes for both spin echo (ΔR2) and gradient echo (ΔR2^*). The areas under the time-ΔR2 and time-ΔR2^* curves were calculated as a semi-quantitative index of GFR for both spin echo and gradient echo images, and the results were compared by GFR measured by radionuclide imaging.Results: The semi-quantitative index of the GFR calculated from spin echo images showed a significant correlation with the GFR measured by radionuclide imaging (r=0.85,P<0.001). On the other hand, the semi-quantitative index of the GFR calculated from gradient echo images showed no such correlation (r=0.46,P=0.10).Conclusion: Spin echo sequences may be more suitable than gradient echo sequences for the evaluation of GFR.     

Volumetric analysis of mice lungs in a clinical magnetic resonance imaging scanner

Small animal models are widely used to study various pathologies. Magnetic resonance imaging (MRI) allows investigation of these animals in a non-invasive way. Therefore, the aim of our study was to develop and evaluate a low-cost approach to measure lung volumes in small animal MRI using a clinical scanner and a specially designed RF coil. Five mice (three of an established emphysema model and two controls) were investigated in a 1.0-T clinical scanner using a specially built small animal saddle coil and three different three-dimensional sequences; overall imaging time was approximately 16 min. Lung volumes were calculated from these images using an interactive watershed transform algorithm for semi-automatic image segmentation. The gold standard for the volume measurement was water displacement after surgical explantation. MRI measured volumes correlated significantly with ex vivo measurements on the explanted lungs (r = 0.99 to 0.89; p < 0.05). Mean lung volume in emphysema model mice was larger than in controls. High-resolution, small animal MRI using a clinical scanner is feasible for volumetric analysis and provides an alternative to a dedicated small animal scanner.     

The feasibility of a novel limited field of view spiral cine DENSE sequence to assess myocardial strain in dilated cardiomyopathy

Objective

Develop an accelerated cine displacement encoding with stimulated echoes (DENSE) cardiovascular magnetic resonance (CMR) sequence to enable clinically feasible myocardial strain evaluation in patients with dilated cardiomyopathy (DCM).

Materials and methods

A spiral cine DENSE sequence was modified by limiting the field of view in two dimensions using in-plane slice-selective pulses in the stimulated echo. This reduced breath hold duration from 20RR to 14RR intervals. Following phantom and pilot studies, the feasibility of the sequence to assess peak radial, circumferential, and longitudinal strain was tested in control subjects (n = 18) and then applied in DCM patients (n = 29).

Results

DENSE acquisition was possible in all participants. Elements of the data were not analysable in 1 control (6%) and 4 DCM r(14%) subjects due to off-resonance or susceptibility artefacts and low signal-to-noise ratio. Peak radial, circumferential, short-axis contour strain and longitudinal strain was reduced in DCM patients (p < 0.001 vs. controls) and strain measurements correlated with left ventricular ejection fraction (with circumferential strain r = − 0.79, p < 0.0001; with vertical long-axis strain r = − 0.76, p < 0.0001). All strain measurements had good inter-observer agreement (ICC > 0.80), except peak radial strain.

Discussion

We demonstrate the feasibility of CMR strain assessment in healthy controls and DCM patients using an accelerated cine DENSE technique. This may facilitate integration of strain assessment into routine CMR studies.

     

Investigating the state-of-the-art in whole-body MR-based attenuation correction: an intra-individual,inter-system,inventory study on three clinical PET/MR systems

Objective

We assess inter- and intra-subject variability of magnetic resonance (MR)-based attenuation maps (MRμMaps) of human subjects for state-of-the-art positron emission tomography (PET)/MR imaging systems.

Materials and methods

Four healthy male subjects underwent repeated MR imaging with a Siemens Biograph mMR, Philips Ingenuity TF and GE SIGNA PET/MR system using product-specific MR sequences and image processing algorithms for generating MRμMaps. Total lung volumes and mean attenuation values in nine thoracic reference regions were calculated. Linear regression was used for comparing lung volumes on MRμMaps. Intra- and inter-system variability was investigated using a mixed effects model.

Results

Intra-system variability was seen for the lung volume of some subjects, (p = 0.29). Mean attenuation values across subjects were significantly different (p < 0.001) due to different segmentations of the trachea. Differences in the attenuation values caused noticeable intra-individual and inter-system differences that translated into a subsequent bias of the corrected PET activity values, as verified by independent simulations.

Conclusion

Significant differences of MRμMaps generated for the same subjects but different PET/MR systems resulted in differences in attenuation correction factors, particularly in the thorax. These differences currently limit the quantitative use of PET/MR in multi-center imaging studies.

     

The C-neu mammary carcinoma in Oncomice; characterization and monitoring response to treatment with herceptin by magnetic resonance methods

To characterize spontaneously occurring c-neu/HER2 overexpressing tumours in oncomice and their response to herceptin by non-invasive magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI). Oncomice were monitored by localized ³¹P MRS during unperturbed growth and before and after treatment with 10 mg/kg herceptin (Hoffman La Roche) intraperitoneally for up to 21 days post-treatment. Vascular morphology and function was assessed by quantitation of tumour magnetic resonance (MR) relaxation rates R₂* and R₂ prior to and either during carbogen (95% O₂/5% CO₂) breathing or following administration of the blood-pool contrast agent NC100150 (Clariscan, Amersham Health). Immunohistochemistry showed strong membrane staining for HER2 protein overexpression. The ³¹P MRS showed only a significant (p<0.01) increase of phosphomonoester / total phosphate ratio over 21 days of growth. Herceptin increased the tumour volume doubling time compared to untreated tumours and significantly increased the phosphomonoester / -nucleoside triphosphate ratio 2 days after treatment (p=0.01). Tumours showed a highly heterogeneous yet significant (p<0.01) decrease or increase in R₂* in response to carbogen or NC100150 respectively. The absence of a decline in tumour bioenergetics with growth, commonly seen in ³¹P MRS studies of transplanted rodent tumour models, coupled with the heterogeneous blood volume revealed by ¹H MRI, suggest a metabolic and vascular phenotype similar to that found in human tumours.     

MRI correlates of disease course and activity in multiple sclerosis

We have carried out a comparative cross-sectional study of patients with relapsing and remitting MS (multiple sclerosis) (RRMS) (n=9), primary progressive MS (PPMS) (n=7), and secondary progressive MS (SPMS) (n=10) using image analysis techniques to determine the number and volume of Gd-DTPA-enhancing lesions. RRMS patients had more lesions than either PPMS or SPMS (ns), and the mean volume of the lesions (p=0.006) and the total volume of enhancing lesions (p<0.03) were significantly larger in patients with RRMS compared with PPMS. The prevalence of blood-brain barrier (BBB) breakdown appears to be similar in PPMS and SPMS, with the higher rate in RRMS suggesting a suppressive effect of disease duration (and/or age). Similarly, the volume of the lesion load overall was negatively correlated with disease duration (p –0.56,p<0.003). Differences between PPMS and RRMS/SPMS patients in the volume of the enhancing lesions may reflect differences in the ability of these patients to suppress the immune-mediated damage to axons which may follow episodic BBB breakdown and which is not visualized on conventional magnetic resonance imaging.     

Magnetic resonance imaging of the pituitary gland in patients with secondary hypogonadism due to transfusional hemochromatosis

To identify pituitary iron overload in patients with transfusional hemochromatosis causing secondary hypogonadism, we prospectively evaluated signal intensity abnormalities of the anterior lobe of the pituitary gland of 18 patients affected by transfusion-dependent thalassemia major and secondary hypogonadism. Magnetic resonance (MR) imaging is useful to assess pituitary iron overload in patients with transfusional hemochromatosis and secondary hypogonadism by detection of a significant decreased signal intensity of the anterior lobe of the pituitary gland on GRE T2^*-weighted images. The decreased signal intensity of the anterior lobe of the pituitary gland on GRE T2^*-weighted images was correlated to increasing serum ferritin level (r=−0.84,r ²=−0.70,P<0.001). Indeed, the lower the signal intensity of the pituitary gland the greater the serum ferritin level. However an exact quantification of pituitary iron overload by correlation with serum ferritin level is not allowed. No correlation was found between MR imaging results and hormonal status; however, the detection of pituitary iron overload on GRE T2^*-weighted images is consistent with the hypothesis of hypogonadotrophic pituitary insufficiency due to iron-induced cellular damage.     

Use of spin-traps during warm ischemia-reperfusion in rat liver: comparative effect on energetic metabolism studied using31P nuclear magnetic resonance

Detection of free radicals by electron spin resonance (ESR) proves the involvement of reactive oxygen species (ROS) in reperfused organ injuries. Spin-traps are known to ameliorate hemodynamic parameters in an isolated postischemic heart. The effects of 5 mmol/L DMPO (5,5-dimethyl-1-pyrroline-N-oxide) or DEPMPO (5-(diethylphosphoryl)-5-methyl-1-pyrrolineN-oxide) on intracellular pH (pH_in) and ATP level were evaluated by³¹P nuclear magnetic resonance on isolated rat liver submitted to 1 hour of warm ischemia and reperfusion. At the end of the reperfusion period, during which pH_in recovered to its initial value (7.16±0.03) in all groups, the ATP recovery level (expressed in percentage of initial value) was similar in controls and DEPMPO (60%±5%,n=6 and 54%±4%,n=6, respectively), but only 37%±1% in DMPO-treated livers (n=6) (p<0.05 versus controls andp<0.05 versus DEPMPO). Oxidative phosphorylation was not affected by an addition of nitrones on isolated mitochondria extracted from livers not submitted to ischemia-reperfusion. In contrast, mitochondria extracted at the end of the ischemia-reperfusion showed an impairment in the phosphorylation parameters, particularly in the presence of DMPO. Mass spectrum of ischemic liver perchloric acid extracts evidenced probable catabolites in treated groups. The differences in the effect of the two nitrones on energetic metabolism may be explained by the production of deleterious catabolites by DMPO as compared to DEPMPO. Even though a specific radical scavenging effect could be operative in the liver, our results indicate that catabolic effects were predominant. The absence of deleterious effects of DEPMPO in contrast to DMPO on the liver energetic metabolism was evidenced, allowing the use of DEPMPO for ESR detection.     

Das Magnetfeld eines gleichstromdurchflossenen Torus

Übersicht Es wird das Magnetfeld eines gleichstromdurchflossenen Torus berechnet, wobei für die Stromdichteverteilung im Inneren des TorusS=S _m r ^m (m ganz) gelten soll. Als Beispiel wird im Fallem=0 und –1 das Magnetfeld im Zentrum des Torus berechnet.

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Contents The magnetic field of a torus is derived for current density distributions in the interior of the torus following the relationS=S _m r ^m (m integer). As an example the magnetic field in the center of the torus is calculated for the valuesm=0 and –1.

     

Magnetic resonance imaging of coronary arteries and coronary stenosis

Coronary artery imaging is an important investigation for the management of coronary artery disease. Alternative noninvasive imaging would be useful, but the small caliber and tortuosity of the coronary vessels and cardiac and respiratory motion create formidable imaging problems. We first studied 21 normal subjects and 5 with coronary artery disease established by X-ray contrast angiography, of whom 2 had undergone bypass grafting. Of these, 22 were imaged successfully. Identification of the artery was possible for the left main stem, left anterior descending, right coronary, and left circumflex arteries respectively in 95%, 91%, 95%, and 76%. The arterial diameter at the origin could be measured in 77%, 77%, 81%, and 63%. The mean ±SD arterial diameter in each case (4.8±0.8, 3.7±0.5, 3.9±0.9, and 2.9±0.6 mm) was not significantly different from reference values (allp=ns). The mean length of artery visualized was 10.4±5.2,46.7±22.8,53.7±27.9, and 26.3±17.5 mm. In 12 normal males, the total coronary area was 30.9±9.2 mm² and the ratio compared with body surface area was 16.4±4.4 mm² m^–2 (bothp=ns compared with reference values). In seven patients, with X-ray contrast coronary angiography, the proximal arterial diameter measured by magnetic resonance was 3.9±1.1 mm, and by X-ray contrast angiography 3.7±1.0 mm (p=ns). We then studied 17 patients with angina. Imaging of just the relevant artery was performed and analysis was blinded to the X-ray angiography results. Stenosis was identified on the magnetic resonance (MR) images by localized reduction in vessel signal intensity. Stenosis location by MR was assessed by measurement of its distance from a reference vessel, with correlation to the X-ray findings. X-ray coronary angiography showed 23 stenoses of which 15 (65%) were correctly located by blind assessment of the MR images. Of the eight remaining stenoses, a further 5 (63%) were correctly located on the MR images after retrospective comparison (overall sensitivity 87%). There were three lesions thought to represent stenosis by MR, which on review of the X-ray angiogram proved to be a minor stenosis <50% (two cases) or a tortuous vessel (one case). Greater signal loss was seen in the more severe stenoses. The stenosis length by MRI was greater than by X-ray (8.4 versus 5.1 mm,p<0.001). The overestimation of stenosis length may be due to turbulence.     

Sex,body mass index,and blood pressure are related to aortic characteristics in healthy,young adults using magnetic resonance vessel wall imaging: the AMBITYON study

Objectives

More detailed evaluation of atherosclerosis and its key determinants in young individuals is warranted to improve knowledge on the pathophysiology of its development and progression. This study evaluated associations of magnetic resonance imaging (MRI)-derived aortic wall area, wall thickness, and pulse wave velocity (PWV) with cardiovascular risk factors in asymptomatic, young adults.

Materials and methods

In 124 adults (age: 25–35 years) from the general population-based Atherosclerosis Monitoring and Biomarker Measurements in the Young study, demography, anthropometry, and blood samples were collected. The studied MRI-parameters were measured using a 3.0T MRI system. Relations between cardiovascular risk factors and aortic characteristics were assessed using multivariable linear regression analyses.

Results

Mean age was 31.8 years, 47.6% was male. Aortic wall area was positively associated with age [β = 0.01, (95% confidence interval (CI) 2.00 × 10^?3, 0.02), p = 0.01] and BMI [β = 0.01, (0.01, 0.02), p = 0.003] and negatively associated with sex (reference: men) [β = ?0.06, (?0.11, ?0.01), p = 0.02]. Natural logarithm transformed (ln) aortic wall thickness was positively associated with BMI [β = 0.01, (1.00 × 10^?3, 0.02), p = 0.02]. Ln aortic PWV was positively associated with 10 mmHg increment of SBP [β = 0.06, (0.03, 0.09), p < 0.001] and DBP [β = 0.06, (0.02, 0.09), p = 0.006]. No relations were observed for smoking and lipids.

Conclusions

Already in early adulthood, aortic wall geometry and stiffness vary by age, sex, BMI, and blood pressure.

     

Spin-spin relaxation times in myocardial hypertrophy induced by endocrine agents in rat

Magnetic resonance techniques afford a significant advantage for noninvasive diagnosis of cardiovascular pathology. The purpose of our present study was to assay the proton nuclear magnetic resonance (¹H-NMR) sensitivity in the differential diagnosis of certain endocrine cardiovascular complications. In this context, we investigated the water state and content in the hypertrophied myocardium. Male and female Wistar rats were treated with different hormones (hydrocortisone acetate, testosterone, estradiol, thyroid hormones) in combination with isoproterenol (a synthetic catecholamine that induces myocardial ischemia and hypertrophy). The animals were sacrificed after 20 days of treatment and samples of integral myocardium and left ventricular myocardium were analyzed on a¹H-NMR AREMI spectrometer (0.6 T; proton resonance at 25 MHz). The estimation ofT ₂ was made by Carr-Purcell-Meiboom-Gill pulse sequence. The data were fitted to a bi-exponential curve, yielding short (T ₂₁) values forbound water and long (T ₂₂) values forfree water. In order to evaluate the myocardial hypertrophy, the following ratios were calculated: integral myocardium to body weight; left ventricle to body weight; left ventricle to integral myocardium. The first two ratios were also calculated for dried tissue, in order to estimate its contribution to myocardial hypertrophy. Our findings demonstrate that myocardial hypertrophy is associated with a decrease ofT ₂₂, as a consequence of the increase in the dried component (i.e. proteins) of the tissue, while the total tissue, while the total tissue water (H₂O_t%, measured by gravimetry) was not significantly modified. Nevertheless, it is reasonable that the increase in the protein content would be proportional with the increase in H₂O_t%. The decrease ofT ₂₁ seems to be proportional with the level of left ventricle hypertrophy in female groups. The¹H-NMR measurements were much sensitive for the differential diagnosis of myocardial hypertrophy in the case of left ventricle.     

Kraft auf einen exzentrisch gelagerten Zylinder im Felde eine mehrpoligen Wechselstromwicklung

Übersicht Ein leitender Zylinder ist exzentrisch in einer Statorbohrung gelagert, die eine 2p-polige Wechselstromwicklung mitq Nuten pro Pol trägt. Die Materialeigenschaften des Zylinders und die Frequenz des erregenden Stromes sind so beschaffen, daß das resultierende magnetische Feld tangential zur Zylinderoberfläche verläuft. Aufgestellt werden allgemeine Beziehungen für die Kraft auf den leitenden Zylinder, die dann aus den Abmessungen der Anordnung berechnet werden kann. Die zentrierende Kraft wird fürp=2 undq=1 berechnet, wobei für den praktisch interessierenden Fall kleiner Luftspalte eine einfache und sehr genaue Näherungsbeziehung angegeben wird.

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Force on cylinder placed eccentrically in field of a multi-poled A.C.-Coil

Contents A conducting cylinder is eccentrically placed in a stator-boring having A.C.-coil with 2p-pols andq slots per pol. The properties of the cylinder-material and the frequency of the exciting current are so selected that the resultant magnetic field is tangential to the cylinder-surface. General expressons for the force exerted by the conducting cylinder are developed which could be evaluated from the dimensions of the configuration. The centering force is calculated forp=2 andq=1, whereby for the case of practically interesting small air-gap a very good and simple approximation for the force is also given.

     

On the realizability of non-rational positive real functions

The paper deals with the analysis and synthesis of passive reciprocal one-ports composed of an infinite number of conventional elements (positive R, L. C and ideal transformers), considered as equivalent circuits of physical distributed one-ports. In the generalization from finite to infinite networks, several (generally overlooked) basic difficulties arise, which are discussed and partially clarified. Physically, a prescribed positive real function z(p) is only specified in Rep > 0, and a lossless infinite realization always exists. Since the value of the function in Re p < 0 is then deduced by z(p) + z(–p) = 0, the resistance r(α, ω) = Re z(α + jω) is such that r(0, ω) = 0, but the limit of r(α, ω) for α = +0 may be strictly positive, so that a lossless impedance may have a resistive behaviour in steady-state. The classical Foster and Cauer synthesis procedures may consequently all fail for lossless non-rational impedances, whereas the procedures of Darlington and Bott-Duffin (and sometimes Brune) succeed. Since every point is a transmission zero for an odd function, a cascade synthesis with all zeros at p = 1 always works, and explicit expressions for the element values are obtained. Many examples are treated in detail, and their sometimes pathological behaviour in Re p < 0 is discussed.     

Influence of cytosolic pH onin vivo assessment of human muscle mitochondrial respiration by phosphorus magnetic resonance spectroscopy

The authors present anin vivo phosphorus magnetic resonance spectroscopy systematic study on the effects of cytosolic pH on skeletal muscle mitochondrial respiration in human calf muscle. In 49 normal subjects, the effect of cytosolic pH on kinetics of phosphocreatine and adenosine diphosphate recovery and on maximum rate of mitochondrial adenosine triphosphate production (Q_max) was evaluation. The results show a strong relationship between the rate of postexercise phosphocreatine recovery and the lowest value of cytosolic pH reached during recovery from exercise (termed minimum pH;r=0.89); in constrast, both adenosine diphosphate recovery halftime andQ _max were independent of cytosolic pH at the end of exercise.     

Overestimation of grey matter atrophy in glioblastoma patients following radio(chemo)therapy

Objective

Brain atrophy has the potential to become a biomarker for severity of radiation-induced side-effects. Particularly brain tumour patients can show great MRI signal changes over time caused by e.g. oedema, tumour progress or necrosis. The goal of this study was to investigate if such changes affect the segmentation accuracy of normal appearing brain and thus influence longitudinal volumetric measurements.

Materials and methods

T1-weighted MR images of 52 glioblastoma patients with unilateral tumours acquired before and three months after the end of radio(chemo)therapy were analysed. GM and WM volumes in the contralateral hemisphere were compared between segmenting the whole brain (full) and the contralateral hemisphere only (cl) with SPM and FSL. Relative GM and WM volumes were compared using paired t tests and correlated with the corresponding mean dose in GM and WM, respectively.

Results

Mean GM atrophy was significantly higher for full segmentation compared to cl segmentation when using SPM (mean ± std: ΔV_GM,full = − 3.1% ± 3.7%, ΔV_GM,cl = − 1.6% ± 2.7%; p < 0.001, d = 0.62). GM atrophy was significantly correlated with the mean GM dose with the SPM cl segmentation (r = − 0.4, p = 0.004), FSL full segmentation (r = − 0.4, p = 0.004) and FSL cl segmentation (r = -0.35, p = 0.012) but not with the SPM full segmentation (r = − 0.23, p = 0.1).

Conclusions

For accurate normal tissue volume measurements in brain tumour patients using SPM, abnormal tissue needs to be masked prior to segmentation, however, this is not necessary when using FSL.

     

MRI-based assessment of liver perfusion and hepatocyte injury in the murine model of acute hepatitis

Objective

To assess alterations in perfusion and liver function in the concanavalin A (ConA)-induced mouse model of acute liver failure (ALF) using two magnetic resonance imaging (MRI)-based methods: dynamic contrast-enhanced MRI (DCE-MRI) with Gd-EOB-DTPA contrast agent and arterial spin labelling (ASL).

Materials and methods

BALB/c mice were studied using a 9.4 T MRI system. The IntraGateFLASH^TM and FAIR-EPI pulse sequences were used for optimum mouse abdomen imaging.

Results

The average perfusion values for the liver of the control and ConA group were equal to 245 ± 20 and 200 ± 32 ml/min/100 g (p = 0.008, respectively). DCE-MRI showed that the time to the peak of the image enhancement was 6.14 ± 1.07 min and 9.72 ± 1.69 min in the control and ConA group (p < 0.001, respectively), while the rate of the contrast wash-out in the control and ConA group was 0.037 ± 0.008 and 0.021 ± 0.008 min^?1 (p = 0.004, respectively). These results were consistent with hepatocyte injury in the ConA-treated mice as confirmed by histopathological staining.

Conclusions

Both the ASL and DCE-MRI techniques represent a reliable methodology to assess alterations in liver perfusion and hepatocyte integrity in murine hepatitis.

     

Gadolinium-containing copolymeric chelates—a new potential MR contrast agent

Rationale and objectives: To develop and partially characterize a new class of potential blood pool magnetic resonance (MR) contrast agents.Methods: Various copolymeric chelates of gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) were prepared with differing molecular weights of polyethylene glycol (PEG) or polypropylene glycol (PPG) as linkers between the monomeric chelate units. Gadolinium content of the polymeric chelates was determined by atomic absorption spectra. Relaxivity of the polymeric chelates was measured at 1.5 Tesla and compared with Gadolinium-DTPA. MR angiography (MRA) was performed in rabbits comparing Gd-DTPA with Gd-copolymers.Results: The gadolinium content of the copolymeric chelates ranged from 2.95 to 22.2% on weight basis. The molecular weight of the PEG linkers in the copolymers ranged from about 150 to about 3400. Ther ₁ (1/T1, mM⁻¹ s⁻¹) for Gd-DTPA=4.1. Ther ₁ values for the different Gd-containing polymers ranged from 3.8 to 5.8, with the lowestr ₁ for the polymer prepared with the lowest-molecular-weight complex. The higher-molecular-weight complexes resulted in moderately higher relaxivity. MRA with Gd-copolymers, in rabbits, showed markedly greater vascular enhancement relative to an equivalent dose of Gd-DTPA. Vascular enhancement was much more sustained with the copolymeric agent and confined to vascular space; i.e. no appreciable background tissue enhancement—a reflection of distribution into extravascular fluid space—was observed.Conclusions: Relative to Gd-DTPA monomers, PEG-containing Gd-DTPA polymeric complexes provided moderate increases in relaxivity but markedly greater efficacy during in vivo MRA. In vitro relaxivity studies of Gd-copolymers showed only an approximately 50% increase inr ₁ relaxivity compared with Gd-DTPA. The PEG-containing complex's lack of rigidity may have diminished the effect of spin diffusion on relaxation, thereby accounting for this modest increase. The greater efficacy of Gd-copolymers during in vivo MRA may reflect compartmentalization within the vascular space and possibly enhanced relaxation of the macromolecular copolymers in the blood. Gd-copolymers are promising agents that merit additional study.     

Automated segmentation and volumetric analysis of renal cortex,medulla, and pelvis based on non-contrast-enhanced T1- and T2-weighted MR images

Object

The aim of our study was to enable automatic volumetry of the entire kidneys as well as their internal structures (cortex, medulla, and pelvis) from native magnetic resonance imaging (MRI) data sets.

Materials and methods

Segmentation of the entire kidneys and differentiation of their internal structures were performed in 12 healthy volunteers based on non-contrast-enhanced T1- and T2-weighted MR images. Two data sets (each acquired in one breath-hold) were co-registered using a rigid registration algorithm compensating for possible breathing-related displacements. An automatic algorithm based on thresholding and shape detection segmented the kidneys into their compartments and was compared to a manual labeling procedure.

Results

The resulting kidney volumes of the automated segmentation correlated well with those created manually (R ² = 0.96). Average volume errors were determined to be 4.97 ± 4.08 % (entire kidney parenchyma), 7.03 ± 5.56 % (cortex), 12.33 ± 7.35 % (medulla), and 17.57 ± 14.47 % (pelvis). The variation of the kidney volume resulting from the automatic algorithm was found to be 4.76 % based on the measuring of one volunteer with three independent examinations.

Conclusion

The results demonstrate the feasibility of an accurate and repeatable automatic segmentation of the kidneys and their internal structures from non-contrast-enhanced magnetic resonance images.