Contrast Agents & Microvascular Function: Methods
Thursday 23 April 2009
Room 316BC 16:00-18:00


Timothy J. Carroll and Linda Knutsson

16:00 719. Measuring the Concentration of Contrast Agent in Blood for DSC MRI from the Extra-Vascular Phase Shift
    Samuel James Wharton1, Natalia Petridou1, Ashley E. Lotfipour1, Penny A. Gowland1, Richard Bowtell1
Sir Peter Mansfield Magnetic Resonance Centre, School of Physics and Astronomy, University of Nottingham, Nottingham, UK
    Recently, it has been shown that the susceptibility of a uniform object with arbitrary geometry can be quantified by least-squares fitting phase data measured in gradient echo imaging to a simulated field-shift. The large phase shifts associated with blood vessels, amplified in the presence of paramagnetic contrast agents, provide ample information for such a fitting process to be applied in-vivo. Here, we present a robust method for directly calculating the susceptibility of blood in the human brain from extra-vascular phase data and describe its application in Dynamic Susceptibility Contrast MRI experiments at 7T.
16:12 720. Robust Quantification of Contrast Agent Concentration with Magnetic Field Correlation Imaging
    Vishal Patil1, Glyn Johnson1, Jens H. Jensen1
Radiology, NYU School of Medicine, New York, USA
    Estimation of gadolinium concentration, [Gd], is the essential first step in the measurement of a number of different parameters by contrast enhanced perfusion MRI. Generally, [Gd] is estimated assuming a linear relationship between relaxation rate and concentration. However, it is known that this assumption is false in tissue. Magnetic Field Correlation (MFC) depends quadratically on [Gd] to a very good approximation and may therefore be a more accurate means of estimating concentration. The purpose of this study is to compare the accuracy of [Gd] measurement using MFC and relaxivity rates in yeast phantoms.
16:24 721. The Effects of Equilibrium Intercompartmental Water Exchange Kinetics on MRI Estimation of Tissue Concentration of Contrast Agents
    Ramesh Paudyal1,2, Hassan Bagher-Ebadian1,2, Tavarekere Nagaraja3, Swayam Panda2, Joseph D. Fenstermacher3, James R. Ewing1,2
Physics, Oakland University, Rochester, MI, USA; 2Neurology, Henry Ford Health Systems, Detroit, MI, USA; 3Anesthesiology, Henry Ford Health Systems, Detroit, MI, USA
    This study address the effects of equilibrium intercompartmental water exchange kinetics on the tissue water protons relaxation rate utilizing the Look-Locker pulse sequence for the Bloch McConnell equation of a three site two exchange [3S2X] model, in which paramagnetic relaxation agents (CA) are restricted only to certain compartment. The relationship between the tissue water relaxation rate R1 versus the tissue concentration of CA is examined by using both modeling and experimental methods.
16:36 722. Gas-Filled Microbubbles as Intravascular R2* Contrast Agent for Liver MRI
    April M. Chow1,2, Jerry S. Cheung1,2, Alfred Yu2, Hua Guo1,2, Ed X. Wu1,2
Laboratory of Biomedical Imaging and Signal Processing, The University of Hong Kong, Hong Kong SAR, China; 2Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong SAR, China
    Gas-filled microbubbles possess the potential to become a unique MR contrast agent because of their magnetic susceptibility effect, high biocompatibility and unique cavitation and sonoporation properties. In this study, microbubble susceptibility induced changes were investigated using custom-made albumin-coated microbubbles and a commercially available lipid-based clinical ultrasound contrast agent SonoVue® in rat livers in vivo with dynamic susceptibility weighted MRI at 7T. The results demonstrate the potential of gas-filled microbubble as an intravascular R2* contrast agent for liver MRI at high field.
16:48 723. Repeatable First Pass DSC-MRI Measurements Using Saline as a Reverse-Effect Contrast Agent
    Christopher Chad Quarles1, John Christopher Gore1
Institute of Imaging Science, Radiology and Radiological Sciences, Biomedical Engineering, Vanderbilt University, Nashville, TN, USA
    Dynamic susceptibility contrast MRI provides measures of tissue hemodynamics but is limited to one measurement per imaging session limiting its use for pharmacological and functional studies. The goal of the present study is to assess the potential of saline for use as a reverse-effect contrast agent for multiple DSC-MRI measurements. This method relies on the reduction of the blood signal intensity using a pre-injection of an iron oxide contrast agent prior to a bolus injection(s) of saline. Saline enhanced the signal intensity by 25% and yielded dynamic time series similar to those measured with a conventional contrast agent.
17:00 724. Analysis of Partial Volume Effects on Arterial Input Functions Using Gradient Echo: A Simulation Study
    Birgitte Fuglsang Kjolby1, Irene Klærke Mikkelsen1, Michael Pedersen2, Leif Oestergaard1, Valerij G. Kiselev3
Center for Functionally Integrative Neuroscience, Aarhus University Hospital, Aarhus, Denmark; 2MR Research Center, Aarhus University Hospital, Aarhus, Denmark; 3Department of Diagnostic Radiology, Medical Physics, University Hospital Freiburg, Freiburg, Germany
    Quantitative perfusion weighted MRI requires an accurately measured arterial input function (AIF). Due to limited spatial resolution, AIF voxels cannot be placed completely within a feeding artery. We present a two-compartment model of an AIF voxel including relaxation properties of blood and tissue. The aim is to analyze the shape of partial volumed AIF signals and quantify the impact of partial volume effects on the quantitative perfusion metrics. We find that the tissue contribution broadens and introduces fluctuations in the AIF. Furthermore, PVE bias perfusion metrics in a nonlinear fashion, compromising quantitative perfusion estimates and profoundly effecting local AIF selection.
17:12 725. Phase Contrast MRI Absolute Cerebral Blood Flow Estimation: A Method to Obtain Absolute Cerebral Blood Flow Maps from Dynamic Susceptibility Contrast Imaging
    David Bonekamp1, Peter B. Barker2
Johns Hopkins University, Baltimore, MD, USA; 2Johns Hopkins University, USA
    We propose a method to calibrate dynamic susceptibility contrast MRI (DSC-MRI) relative cerebral blood flow (rCBF) maps using a single slice phase contrast MRI (PC-MRI) technique to obtain absolute cerebral blood flow (tCBF) maps. This technique requires only a minimal extension of the clinical protocol by a 50 sec sequence. Initial results demonstrate that the white matter CBF estimate in the hemisphere contralateral to the pathology demonstrates significantly less variability and better agreement with literature values than uncorrected data.
17:24 726. A New Constrained Blind Estimation Algorithm for Determination of the Arterial Input Function Without Reference Tissues
    Matthias Christian Schabel1, Edward V. R. Di Bella1
Radiology, University of Utah, Salt Lake City, UT, USA
    We describe an efficient constrained method for blind estimation of the arterial input function that does not require reference tissues or clustering of similar tissue curves. This method has been validated by Monte Carlo simulations and in human subjects with solid tumors, and demonstrates excellent consistency with high-quality measured AIFs as well as reproducibility in longitudinal studies.
17:36 727. Comparison of Arterial Blood Volume Obtained from Model-Free Arterial Spin Labelling (ASL) and Cerebral Blood Volume Obtained from Contrast Enhanced Dynamic Susceptibility Weighted Imaging (DSC) in Brain Tumours
    Danielle van Westen1, Linda Knutsson2, Esben Thade Petersen3,4, Karin Markenroth Bloch5, Freddy Ståhlberg1,6, Stig Holtås1
Department of Diagnostic Radiology, Lund University, Lund, Sweden; 2Department of Medical Radiation Physics, Lund University, Lund, Sweden; 3Neuroradiology, National Neuroscience Institute, Singapore, Singapore; 4 CFIN, Aarhus University Hospital, Aarhus, Denmark; 5Philips Medical Systems, Lund, Sweden; 6Department of Medical Radiation Physics, Lund University , Lund, Sweden
    Cerebral blood volume (CBV) in brain tumours can be used to differentiate intracranial tumour types. Measurement of CBV with dynamic susceptibility weighted imaging (DSC-MRI) requires injection of a contrast agent. As an alternative, a recently introduced, model-free arterial spin labelling technique (ASL) named QUASAR enables quantification of CBF and arterial blood volume (aBV). In this study, aBV and CBF calculated from ASL and CBV and CBF obtained from DSC-MRI were determined in three types of brain tumours. We conclude that aBV is a potential tool for characterisation of intracranial tumours, of special clinical interest since its measurement is non-invasive.
17:48 728. Software Solution for Automated Assessment of DWI/PWI Mismatch in Acute Stroke Patients: The RAPID MISMATCH
    Matus Straka1, Maarten G. Lansberg2, Gregory W. Albers2, Roland Bammer1
Lucas Center, Department of Radiology, Stanford University, Stanford, CA, USA; 2Stroke Center, Department of Neurology and Neurological Sciences, Stanford University, Stanford, CA, USA
    DWI/PWI mismatch is method to identify acute stroke patients that might benefit from reperfusion therapies. We have implemented a fully automated system aimed on assessment of mismatch from DWI and Tmax perfusion maps. The automated approach can deliver the mismatch maps within 5 minutes after the scan to scanner and PACS. The statistical evaluation of 74 cases has shown robustness of the system and good correlanion between manual and automated results.