Simultaneous multislice acquisition with multi-contrast segmented EPI for separation of signal contributions in dynamic contrast-enhanced imaging

We present a method to efficiently separate signal in magnetic resonance imaging (MRI) into a base signal S0, representing the mainly T1-weighted component without T2*-relaxation, and its T2*-weighted counterpart by the rapid acquisition of multiple contrasts for advanced pharmacokinetic modelling. This is achieved by incorporating simultaneous multislice (SMS) imaging into a multi-contrast, segmented echo planar imaging (EPI) sequence to allow extended spatial coverage, which covers larger body regions without time penalty. Simultaneous acquisition of four slices was combined with segmented EPI for fast imaging with three gradient echo times in a preclinical perfusion study. Six female domestic pigs, German-landrace or hybrid-form, were scanned for 11 minutes respectively during administration of gadolinium-based contrast agent. Influences of reconstruction methods and training data were investigated. The separation into T1- and T2*-dependent signal contributions was achieved by fitting a standard analytical model to the acquired multi-echo data. The application of SMS yielded sufficient temporal resolution for the detection of the arterial input function in major vessels, while anatomical coverage allowed perfusion analysis of muscle tissue. The separation of the MR signal into T1- and T2*-dependent components allowed the correction of susceptibility related changes. We demonstrate a novel sequence for dynamic contrast-enhanced MRI that meets the requirements of temporal resolution (Δt < 1.5 s) and image quality. The incorporation of SMS into multi-contrast, segmented EPI can overcome existing limitations of dynamic contrast enhancement and dynamic susceptibility contrast methods, when applied separately. The new approach allows both techniques to be combined in a single acquisition with a large spatial coverage

Establishment of a Swine Model for Validation of Perfusion Measurement by Dynamic Contrast-Enhanced Magnetic Resonance Imaging

The aim of the study was to develop a suitable animal model for validating dynamic contrast-enhanced magnetic resonance imaging perfusion measurements. A total of 8 pigs were investigated by DCE-MRI. Perfusion was determined on the hind leg musculature. An ultrasound flow probe placed around the femoral artery provided flow measurements independent of MRI and served as the standard of reference. Images were acquired on a 1.5 T MRI scanner using a 3D T1-weighted gradient-echo sequence. An arterial catheter for local injection was implanted in the femoral artery. Continuous injection of adenosine for vasodilation resulted in steady blood flow levels up to four times the baseline level. In this way, three different stable perfusion levels were induced and measured. A central venous catheter was used for injection of two different types of contrast media. A low-molecular weight contrast medium and a blood pool contrast medium were used. A total of 6 perfusion measurements were performed with a time interval of about 20-25 min without significant differences in the arterial input functions. In conclusion the accuracy of DCE-MRI-based perfusion measurement can be validated by comparison of the integrated perfusion signal of the hind leg musculature with the blood flow values measured with the ultrasound flow probe around the femoral artery

In vivo assessment of catheter positioning accuracy and prolonged irradiation time on liver tolerance dose after single-fraction 192Ir high-dose-rate brachytherapy

<p>Abstract</p> <p>Background</p> <p>To assess brachytherapy catheter positioning accuracy and to evaluate the effects of prolonged irradiation time on the tolerance dose of normal liver parenchyma following single-fraction irradiation with ¹⁹²Ir.</p> <p>Materials and methods</p> <p>Fifty patients with 76 malignant liver tumors treated by computed tomography (CT)-guided high-dose-rate brachytherapy (HDR-BT) were included in the study. The prescribed radiation dose was delivered by 1 - 11 catheters with exposure times in the range of 844 - 4432 seconds. Magnetic resonance imaging (MRI) datasets for assessing irradiation effects on normal liver tissue, edema, and hepatocyte dysfunction, obtained 6 and 12 weeks after HDR-BT, were merged with 3D dosimetry data. The isodose of the treatment plan covering the same volume as the irradiation effect was taken as a surrogate for the liver tissue tolerance dose. Catheter positioning accuracy was assessed by calculating the shift between the 3D center coordinates of the irradiation effect volume and the tolerance dose volume for 38 irradiation effects in 30 patients induced by catheters implanted in nearly parallel arrangement. Effects of prolonged irradiation were assessed in areas where the irradiation effect volume and tolerance dose volume did not overlap (mismatch areas) by using a catheter contribution index. This index was calculated for 48 irradiation effects induced by at least two catheters in 44 patients.</p> <p>Results</p> <p>Positioning accuracy of the brachytherapy catheters was 5-6 mm. The orthogonal and axial shifts between the center coordinates of the irradiation effect volume and the tolerance dose volume in relation to the direction vector of catheter implantation were highly correlated and in first approximation identically in the T1-w and T2-w MRI sequences (<it>p </it>= 0.003 and <it>p </it>< 0.001, respectively), as were the shifts between 6 and 12 weeks examinations (<it>p </it>= 0.001 and <it>p </it>= 0.004, respectively). There was a significant shift of the irradiation effect towards the catheter entry site compared with the planned dose distribution (<it>p </it>< 0.005). Prolonged treatment time increases the normal tissue tolerance dose. Here, the catheter contribution indices indicated a lower tolerance dose of the liver parenchyma in areas with prolonged irradiation (<it>p </it>< 0.005).</p> <p>Conclusions</p> <p>Positioning accuracy of brachytherapy catheters is sufficient for clinical practice. Reduced tolerance dose in areas exposed to prolonged irradiation is contradictory to results published in the current literature. Effects of prolonged dose administration on the liver tolerance dose for treatment times of up to 60 minutes per HDR-BT session are not pronounced compared to effects of positioning accuracy of the brachytherapy catheters and are therefore of minor importance in treatment planning.</p

Radiobiological restrictions and tolerance doses of repeated single-fraction hdr-irradiation of intersecting small liver volumes for recurrent hepatic metastases

<p>Abstract</p> <p>Background</p> <p>To assess radiobiological restrictions and tolerance doses as well as other toxic effects derived from repeated applications of single-fraction high dose rate irradiation of small liver volumes in clinical practice.</p> <p>Methods</p> <p>Twenty patients with liver metastases were treated repeatedly (2 - 4 times) at identical or intersecting locations by CT-guided interstitial brachytherapy with varying time intervals. Magnetic resonance imaging using the hepatocyte selective contrast media Gd-BOPTA was performed before and after treatment to determine the volume of hepatocyte function loss (called pseudolesion), and the last acquired MRI data set was merged with the dose distributions of all administered brachytherapies. We calculated the BED (biologically equivalent dose for a single dose d = 2 Gy) for different α/β values (2, 3, 10, 20, 100) based on the linear-quadratic model and estimated the tolerance dose for liver parenchyma D₉₀as the BED exposing 90% of the pseudolesion in MRI.</p> <p>Results</p> <p>The tolerance doses D₉₀after repeated brachytherapy sessions were found between 22 - 24 Gy and proved only slightly dependent on α/β in the clinically relevant range of α/β = 2 - 10 Gy. Variance analysis showed a significant dependency of D₉₀with respect to the intervals between the first irradiation and the MRI control (p < 0.05), and to the number of interventions. In addition, we observed a significant inverse correlation (p = 0.037) between D₉₀and the pseudolesion's volume. No symptoms of liver dysfunction or other toxic effects such as abscess formation occurred during the follow-up time, neither acute nor on the long-term.</p> <p>Conclusions</p> <p>Inactivation of liver parenchyma occurs at a BED of approx. 22 - 24 Gy corresponding to a single dose of ~10 Gy (α/β ~ 5 Gy). This tolerance dose is consistent with the large potential to treat oligotopic and/or recurrent liver metastases by CT-guided HDR brachytherapy without radiation-induced liver disease (RILD). Repeated small volume irradiation may be applied safely within the limits of this study.</p

Pharmacokinetic magnetic resonance imaging

Bei der dynamischen kontrastmittelbasierten Magnetresonanztomographie (dMRT) handelt es sich um eine hochaufl¨osende reproduzierbare Methode zur Darstellung der Austauschparameter und Gewebekompartimente, die auf den gesamten Körper angewendet werden kann. Für die Magnetresonanztomographie standen bisher nur niedermolekulare Gadolinium (Gd)-haltige Kontrastmittel für klinische Untersuchungen am Menschen zur Verfügung, die sich mit hoher mpfindlichkeit nachweisen lassen und zudem gut verträglich sind. Niedermolekulare Substanzen, wie das Kontrastmittel Gd-DTPA, extravasieren bereits nach wenigen Sekunden. Zur Verbesserung der Separation der Signalanteile von intraund extravaskul¨arem Kontrastmittel wird ein niedermolekulares Kontrastmittel innerhalb weniger Sekunden als Bolus peripher intraven¨os appliziert, so dass es hochkonzentriert durch das Kapillarbett fließt und sich erst anschließend im Blut gleichm¨aßig verteilt. Zur Darstellung der Vaskularisation ist daher nur die erste Phase geeignet, in der sich das Kontrastmittel noch nicht gleichm¨aßig im Blut verteilt hat und noch ¨uberwiegend intravaskul¨ar befindet. Die niedermolekularen Gd-haltigen Kontrastmittel bewirken Ver¨anderungen zweier im MRT messbarer Parameter: Die Verk¨urzung der T1- und der T2-Relaxationszeit. Zur Darstellung des Kontrastmittelbolus k¨onnen beide Effekte herangezogen werden. T1- gewichtete Sequenzen weisen ¨uber einen weiten Bereich einen in erster N¨aherung linearen Zusammenhang zwischen Signal und Kontrastmittelkonzentration auf. Die Signal ¨anderung ist proportional zur Kontrastmittelkonzentration und erm¨oglicht daher f¨ur relativ geringe Konzentrationen die Bestimmung des Gef¨aßvolumens. Bei hohen Kontrastmittelkonzentrationen gehen T1-gewichtete Sequenzen in eine S¨attigung und anschließenden Signalabfall ¨uber. T2/T∗ 2 -gewichtete Sequenzen weisen einen geringen Signalanstieg bei niedrigen Konzentrationen von Gd-haltigen KM auf, der bei etwas h¨oheren Konzentrationen in eine exponentielle Signalabschw¨achung ¨ubergeht. Daher werden T1-gewichtete Sequenzen ¨uberwiegend mit niedrigerer Kontrastmitteldosierung zur Darstellung des Kontrastmittelbolus oder hochdosiert zur Darstellung der Extravasation eingesetzt. T2/T∗2 -gewichtete Sequenzen eignen sich nur zur Darstellung eines hochdosierten Kontrastmittelbolus. Bei Applikation des Kontrastmittels in Form eines Bolus und T1-gewichteter Sequenz k¨onnen weitergehende Methoden eingesetzt werden, die eine quantitative Bestimmung des Gef¨aßvolumens und des interstitiellen Volumens sowie deren Austauschparameter erm¨oglichen. Voraussetzung f¨ur die Anwendung einer solchen Methode ist ein geeignetes pharmakokinetisches Modell und ein darauf basierendes Auswerteverfahren, das die dominierenden Konzentrations- und Austauschprozesse speziell f¨ur das verwendete niedermolekulare Kontrastmittel beschreibt. Ein solches Modell ist in Form eines 3-Kompartmentmodells zuerst f¨ur die pharmakokinetische Bildgebung am Gehirn und dann sp¨ater auch f¨ur die Prostata in der vorliegenden Arbeit erstmals eingesetzt worden. Unter Verwendung des 3-Kompartmentmodells sind in der vorliegenden Arbeit zahlreiche pharmakokinetische Parameter quantitativ zug¨anglich gemacht worden. F¨ur das Blutvolumen ist die diagnostische Relevanz f¨ur die Gliomgradierung im Rahmen einer ROC-Studie untersucht worden. Dabei hat sich ergeben, dass die Treffsicherheit eines Parameters, der aus den quantitativen Blutvolumenverteilungen gewonnen wird, mit denen der Biopsie vergleichbar ist. Die Perfusion ist bei Hirntumoren ein weniger aussagekr ¨aftiger Parameter als das Blutvolumen. Neben Gliomen sind Meningeome und Fernmetastasen untersucht worden. Meningeome weisen ein deutlich erh¨ohtes Blutvolumen gegen¨uber Gliomen auf und unterscheiden sich auch in ihrem Mikromilieu von Gliomen. Die Kontrastmittelextravasation ist in zwei bidirektionale Transportprozessen separiert worden, einen schnellen und einen langsamen, tituliert jeweils als Permeabilit¨at in jeweils separate interstitielle Volumina. Die schnelle Permeabilit¨at eignet sich nur zur Separation von extraaxialen Tumoren (Meningeomen) von intraaxialen Tumoren (Gliomen und Fernmetastasen). Die langsame Permeabilit¨at eignet sich zur Unterscheidung von nekrotisierenden Tumoren, in diesem Fall von Glioblastomen, von niedergradigen Gliomen. Von den Parametern Perfusion, Blutvolumen und interstitiellem Volumen konnte ihre diagnostische Relevanz nachgewiesen werden. Um das unterschiedliche Mikromilieu besser darzustellen sind Streudiagramme eingesetzt worden bei denen das interstitielle Volumen gegen das Blutvolumen aufgetragen wird. Es wurde gezeigt, dass die verschiedenen Tumoridentit¨aten je nach Mikromilieu unterschiedliche Areale in diesen Streudiagrammen besetzen. Das pharmakokinetische Modell ist f¨ur die dMRT der Prostata auf die Auswertung auf die neue Tumoridentit¨at ¨ubertragen worden. Bisher wurde die dMRT f¨ur die Beurteilung des Prostatakarzinoms nur von wenigen Arbeitsgruppen eingesetzt, wobei ¨uberwiegend auf eine Quantifizierung der Kompartimente und der Austauschkonstanten verzichtet worden war. Aufgrund der zum Gehirn unterschiedlichen Perfusionsverh¨altnisse wurden eine neuartige Doppelkontrastsequenz f¨ur die dynamische Bildgebung eingesetzt, bei der auch der Kontrastmittelbolus im Prostatagewebe dargestellt werden konnte. Zur Auswertung der dynamischen Bilder der Prostata wurde die Auswertemethode und das pharmakokinetischen Modell weiterentwickelt. Im Gegensatz zur Auswertung am Gehirn wurde eine Intensit¨atshomogenisierung und eine Bewegungskorrektur der Auswertung vorgeschaltet. Die Pulsationen der AIF wurden anhand der Phasenbilder korrigiert. Zur Beschreibung der Anflutung war es erforderlich, zus¨atzlich zur verz¨ogerten Ankunftszeit gegen¨uber der AIF die Bolusdispersion zu ber¨ucksichtigen. Als zus¨atzliche Parameter konnten durch die Verwendung eines zweiten Echos mit deutlich verl¨angerter Echozeit die mittlere Transferzeit und die Perfusion quantifiziert werden. Es konnte gezeigt werden, dass die Tumorperfusion in Prostatatumoren signifikant gegen¨uber Prostatagewebe erh¨oht ist. Im Unterschied zu Hirntumoren konnte gezeigt werden, dass bei Prostatatumoren die Perfusion der aussagekr¨aftigere Parameter gegen¨uber dem Blutvolumen ist. Insgesamt erm¨oglicht die 3-Kompartimentauswertung, die Gewebeparameter detailliert und ¨ortlich aufgel¨ost darzustellen.Dynamic contrast-enhanced magnetic resonance imaging (dMRI) is a reproducible technique for determining exchange parameters and tissue compartments with high resolution throughout the human body. In the past, only low-molecular- weight, gadolinium (Gd)-based contrast agents were approved for clinical MRI in humans. Gd contrast agents are well tolerated, and MRI is highly sensitive in demonstrating their effects. Low-molecular-weight contrast media such as Gd-DTPA extravasate within a few seconds of injection. To improve separation of the signal contributions from intra- and extravascular contrast material, a low-molecular weight agent is injected into a peripheral vein as a rapid bolus over a few seconds. The contrast bolus flows through the capillary bed in highly concentrated form before it disperses evenly in the blood. Imaging of vascularization must capture the initial phase after injection when most of the administered bolus is still in the vessel and has not yet dispersed in blood. Low-molecular-weight Gd-based contrast media alter two parameters that can be measured by MRI: they shorten T1 and T2 relaxation times. Both effects can be used to visualize a bolus of contrast medium. In a first approximation, T1-weighted sequences provide images with a linear relationship between signal intensity and contrast medium concentration over a wide range. Signal changes are proportional to contrast medium concentrations and thus enable determination of vascular volume at rather low concentrations. High contrast medium concentrations lead to saturation and subsequent signal loss on T1-weighted sequences. On T2/T2*-weighted sequences, low concentrations of Gd- based contrast medium cause a slight signal loss with a subsequent exponential signal decrease at slightly higher concentrations. For these reasons, T1-weighted sequences are predominantly used to depict the contrast bolus at low contrast medium concentrations or extravasation at high concentrations. T2/T2*-weighted sequences only visualize a high-dose contrast bolus. The combination of T1-weighted MR imaging with bolus injection of contrast medium enables use of more sophisticated techniques for quantitative determination of vascular and interstitial volumes and exchange parameters. Such techniques rely on evaluation methods and a suitable pharmacokinetic model that specifically describes the predominant concentration and exchange processes for the low-molecular-weight contrast medium used. A model found to be suitable for this purpose is a 3-compartment model. Such a model has been used for pharmacokinetic imaging of the brain before and is for the first time applied to the prostate in the present study. In the present study, a number of pharmacokinetic parameters could be quantified using the 3 compartment model. The diagnostic relevance of blood volume was investigated for glioma grading in a ROC analysis. The results suggest that the accuracy of a parameter derived from quantitative blood volume distributions is comparable to that of biopsy. Perfusion is a less relevant parameter than blood volume in assessing brain tumors. Other tumors investigated were meningiomas and distant metastases. Meningiomas differ from gliomas in two respects: they have a markedly larger blood volume and different microenvironment. Contrast medium extravasation has been divided into two bidirectional transport processes – one fast and one slow – which are also known as permeability into two separate interstitial volumes. Fast permeability can only serve to differentiate extra- axial tumors (meningiomas) from intra-axial tumors (gliomas and distant metastases). Slow permeability can be used to characterize necrotic tumors and thus allows differentiation of glioblastomas from low-grade gliomas in the brain. Perfusion, blood volume, and interstitial volume have been shown to be diagnostically relevant parameters. To improve representation of differences in microenvironment, scatter diagrams were used in which interstitial volume is plotted against blood volume. The results show that, based on their microenviroments, different tumor entities occupy different areas in such diagrams. For dMRI of the prostate, the pharmacokinetic model has been extended to encompass prostate cancer as a new tumor entity. Only a few study groups have so far used dMRI for imaging of prostate cancer, and most investigators did not quantify compartments and exchange constants. Since perfusion in the prostate is not the same as in the brain, a novel dual- contrast pulse sequence was used for dMRI. This sequence also visualizes the contrast bolus in prostate tissue. The evaluation method and pharmacokinetic model were further modified for analysis of dMRI of the prostate. The refined method differs from that used for analysis of cerebral MRI in that additional intensity homogenization and motion correction are applied prior to analysis. Phase images are used to correct for pulsations of the AIF. It is necessary to take into account not only delay relative to the AIF but also bolus dispersion in order to adequately describe arrival of contrast medium at the target site. The dual echo sequence with use of a markedly longer echo time for the second echo enabled quantification of mean transfer time and perfusion as additional parameters. It was shown that perfusion is significantly higher in prostate cancer compared with normal prostate tissue. Unlike for brain tumors, it was found that perfusion is a more relevant parameter than blood volume for prostate imaging. In conclusion, use of a 3-compartment model enables detailed and spatially resolved analysis of tissue parameters

Nonrigid 3D Medical Image Registration and Fusion Based on Deformable Models

For coregistration of medical images, rigid methods often fail to provide enough freedom, while reliable elastic methods are available clinically for special applications only. The number of degrees of freedom of elastic models must be reduced for use in the clinical setting to archive a reliable result. We propose a novel geometry-based method of nonrigid 3D medical image registration and fusion. The proposed method uses a 3D surface-based deformable model as guidance. In our twofold approach, the deformable mesh from one of the images is first applied to the boundary of the object to be registered. Thereafter, the non-rigid volume deformation vector field needed for registration and fusion inside of the region of interest (ROI) described by the active surface is inferred from the displacement of the surface mesh points. The method was validated using clinical images of a quasirigid organ (kidney) and of an elastic organ (liver). The reduction in standard deviation of the image intensity difference between reference image and model was used as a measure of performance. Landmarks placed at vessel bifurcations in the liver were used as a gold standard for evaluating registration results for the elastic liver. Our registration method was compared with affine registration using mutual information applied to the quasi-rigid kidney. The new method achieved 15.11% better quality with a high confidence level of 99% for rigid registration. However, when applied to the quasi-elastic liver, the method has an averaged landmark dislocation of 4.32 mm. In contrast, affine registration of extracted livers yields a significantly () smaller dislocation of 3.26 mm. In conclusion, our validation shows that the novel approach is applicable in cases where internal deformation is not crucial, but it has limitations in cases where internal displacement must also be taken into account

Validation of Perfusion Quantification with 3D Gradient Echo Dynamic Contrast-Enhanced Magnetic Resonance Imaging Using a Blood Pool Contrast Agent in Skeletal Swine Muscle.

The purpose of our study was to validate perfusion quantification in a low-perfused tissue by dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) with shared k-space sampling using a blood pool contrast agent. Perfusion measurements were performed in a total of seven female pigs. An ultrasonic Doppler probe was attached to the right femoral artery to determine total flow in the hind leg musculature. The femoral artery was catheterized for continuous local administration of adenosine to increase blood flow up to four times the baseline level. Three different stable perfusion levels were induced. The MR protocol included a 3D gradient-echo sequence with a temporal resolution of approximately 1.5 seconds. Before each dynamic sequence, static MR images were acquired with flip angles of 5°, 10°, 20°, and 30°. Both static and dynamic images were used to generate relaxation rate and baseline magnetization maps with a flip angle method. 0.1 mL/kg body weight of blood pool contrast medium was injected via a central venous catheter at a flow rate of 5 mL/s. The right hind leg was segmented in 3D into medial, cranial, lateral, and pelvic thigh muscles, lower leg, bones, skin, and fat. The arterial input function (AIF) was measured in the aorta. Perfusion of the different anatomic regions was calculated using a one- and a two-compartment model with delay- and dispersion-corrected AIFs. The F-test for model comparison was used to decide whether to use the results of the one- or two-compartment model fit. Total flow was calculated by integrating volume-weighted perfusion values over the whole measured region. The resulting values of delay, dispersion, blood volume, mean transit time, and flow were all in physiologically and physically reasonable ranges. In 107 of 160 ROIs, the blood signal was separated, using a two-compartment model, into a capillary and an arteriolar signal contribution, decided by the F-test. Overall flow in hind leg muscles, as measured by the ultrasound probe, highly correlated with total flow determined by MRI, R = 0.89 and P = 10-7. Linear regression yielded a slope of 1.2 and a y-axis intercept of 259 mL/min. The mean total volume of the investigated muscle tissue corresponds to an offset perfusion of 4.7mL/(min ⋅ 100cm3). The DCE-MRI technique presented here uses a blood pool contrast medium in combination with a two-compartment tracer kinetic model and allows absolute quantification of low-perfused non-cerebral organs such as muscles

Data from: Validation of perfusion quantification with 3D gradient echo dynamic contrast-enhanced magnetic resonance imaging using a blood pool contrast agent in skeletal swine muscle

The purpose of our study was to validate perfusion quantification in a low-perfused tissue by dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) with shared k-space sampling using a blood pool contrast agent. Perfusion measurements were performed in a total of seven female pigs. An ultrasonic Doppler probe was attached to the right femoral artery to determine total flow in the hind leg musculature. The femoral artery was catheterized for continuous local administration of adenosine to increase blood flow up to four times the baseline level. Three different stable perfusion levels were induced. The MR protocol included a 3D gradient-echo sequence with a temporal resolution of approximately 1.5 seconds. Before each dynamic sequence, static MR images were acquired with flip angles of 5°, 10°, 20°, and 30°. Both static and dynamic images were used to generate relaxation rate and baseline magnetization maps with a flip angle method. 0.1 mL/kg body weight of blood pool contrast medium was injected via a central venous catheter at a flow rate of 5 mL/s. The right hind leg was segmented in 3D into medial, cranial, lateral, and pelvic thigh muscles, lower leg, bones, skin, and fat. The arterial input function (AIF) was measured in the aorta. Perfusion of the different anatomic regions was calculated using a one- and a two-compartment model with delay- and dispersion-corrected AIFs. The F-test for model comparison was used to decide whether to use the results of the one- or two-compartment model fit. Total flow was calculated by integrating volume-weighted perfusion values over the whole measured region. The resulting values of delay, dispersion, blood volume, mean transit time, and flow were all in physiologically and physically reasonable ranges. In 107 of 160 ROIs, the blood signal was separated, using a two-compartment model, into a capillary and an arteriolar signal contribution, decided by the F-test. Overall flow in hind leg muscles, as measured by the ultrasound probe, highly correlated with total flow determined by MRI, R = 0.89 and P = 10−7. Linear regression yielded a slope of 1.2 and a y-axis intercept of 259 mL/min. The mean total volume of the investigated muscle tissue corresponds to an offset perfusion of 4.7mL/(min ⋅ 100cm3). The DCE-MRI technique presented here uses a blood pool contrast medium in combination with a two-compartment tracer kinetic model and allows absolute quantification of low-perfused non-cerebral organs such as muscles