Electronic poster

Magnetization Transfer

Hall B Monday 14:00-16:00 Computer 128

14:00 5135. Magnetization Transfer Contrast MRI in GFP-Tagged Live Bacteria

Valeria Righi^1,2, Melissa Starkey³, George Dai², Laurence G. Rahme³, A Aria Tzika<sup>1,2

1</sup>NMR Surgical Laboratory, Department of Surgery, Massachusetts General Hospital and Shriners Burns Institute, Harvard Medical School, Boston, MA, United States; ²Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Athinoula A. Martinos Center for Biomedical Imaging, Boston, MA, United States; ³Molecular Surgery Laboratory, Department of Surgery, Massachusetts General Hospital and Shriners Burns Institute, Harvard Medical School, Boston, MA, United States

We compared wild-type and GFP-tagged cells of Pseudomonas aeruginosa and Escherichia coli bacteria using MRI with Magnetization Transfer Contrast (MTC). This method was sensitive enough to distinguish between GFP-tagged and non-tagged cells at cell concentrations relevant to those used in animal infection models. The significance of this method is that it can be used to visualize bacterial infections in vivo in real time without being restricted to the use of transparent tissue necessary for optical imaging. This method provides a valuable tool to study the impact of novel antibacterial therapeutics.

14:30 5136. Enhancement of MT and CEST Contrast Via Heuristic Fitting of Z-Spectra

Moritz Wilhelm Zaiss¹, Benjamin Schmitt¹, Bram Stieltjes, Peter Bachert<sup>1

1</sup>Medical Physics in Radiology, DKFZ, Heidelberg, Germany

Magnetizations transfer processes are quantified by the evaluation of z-spectra. A superposition of Lorentzian line shape functions, a solution of Bloch equations, is discussed as a heuristic but parametric model for z-spectrum fitting. Numerical, phantom and in vivo studies demonstrate the functionality of this method which is less dependent on exact knowledge of the system and provides enhanced contrast through parameter maps compared to standard asymmetry analysis. The heuristic fit is also less dependent on B₀ inhomogeneities and its parameters can be assigned to physical parameters such as concentration and transfer rates, which are markers for tumour activity.

15:00 5137. A New, 3D GRE Based CEST Imaging Method for Clinical Application and Verification with GagCEST in Articular Cartilage

Benjamin Schmitt¹, Michael Bock¹, Bram Stieltjes, Peter Bachert<sup>1

1</sup>Medical Physics in Radiology, German Cancer Research Center, Heidelberg, Germany

CEST imaging has been introduced as a new method to generate a various number of contrasts for MRI. However, the application of CEST imaging for clinical application has so far been limited by extensive scan-times. These long scan times were necessary to generate reproducible CEST images and often restricted to single-slice acquisitions. We introduce a new, 3D CEST imaging sequence based on RF-spoiled gradient echo which can theoretically be used in a various number of CEST applications. The functionality is exemplified using gagCEST to determine the vitality of knee cartilage in a 3D volume.

15:30 5138. A Comparison of Three CEST Imaging Methods

Zhongliang Zu¹, Ke Li¹, Daniel Frank Gochberg<sup>1

1</sup>Radiology, Vanderbilt University, Nashville, TN, United States

Three CEST imaging methods including continuous-wave, pulsed-, and spoiled gradient recalled CEST are numerically optimized and compared using simulations and a creatine/agarose tissue phantom. We found that the average irradiation power is a more meaningful sequence metric than is the average irradiation field; We also found that the SPGR-CEST provides an alternative to the EPI based CW- and pulsed-CEST imaging methods that avoids the artifacts inherent to multi-echo acquisitions, though at the cost of lower CNR.

Thursday 13:30-15:30 Computer 128

13:30 5147. The Effect of Tissue Erosions and Segmentation Probability Thresholds on Magnetisation Transfer Ratio Histograms

Daniel J. Tozer¹, Sameeha Fallatah¹, Leonora Finisku¹, David H. Miller<sup>1

1</sup>NMR Unit, Department of Neuroinflammation, UCL Institute of Neurology, London, United Kingdom

Magnetisation transfer ratio histograms are widely used in the study of multiple sclerosis. Histogram generation methods may affect the parameters extracted. This work investigates whether the tissue probability threshold used in segmentation and the number of erosions applied to the tissue segments effect the histogram parameters and whether this differs between healthy controls and multiple sclerosis patients. It is found that the number of erosions has more of an effect on the histogram parameters than the probability threshold used, in particular the first erosion. There were some differences between the behaviour in patients and controls, but this was not systematic.

14:00 5148. Fast Bound Pool Fraction Quantification Using Stimulated Echoes

Michaela Soellinger¹, Christian Langkammer¹, Thomas Seifert-Held¹, Franz Fazekas¹, Stefan Ropele<sup>1

1</sup>Department of Neurology, Medical University of Graz, Graz, Austria

The bound proton pool fraction is linked to the lipid and protein content of myelin. Therefore, fast mapping methods are required for patient studies and clinical routine. We introduce a sequence allowing whole brain BPF determination in within clinically feasible time (~5 min for 11 slices). The method is based on the labelling of the free water pool with stimulated echo amplitude modulation (STEAM). The herewith presented approach was validated with bovine serum albumin (BSA) probes and successfully tested in three healthy volunteers. Regional analysis of white matter was in good agreement with published BPF values.

14:30 5149. Correlation Time Diffusion MRI of Mouse Liver at 11.7T: Magnetization Transfer Effects

Hernan Jara¹, Stephan W. Anderson¹, Osamu Sakai¹, Jorge A. Soto<sup>1

1</sup>Boston University School of Medicine, Boston, MA, United States

Purpose: To map the correlation time diffusion coefficient (CT-D) of ex vivo liver samples imaged at 11.7T and to compare results quantitatively vs. the standard pulsed-field gradient (PFG-D) diffusion MRI. Methods: A CT-D algorithm was applied to mouse liver images obtained with Tandem-TSE at 11.7T. Results: Excellent quantitative agreement was found between this non-PFG diffusion technique vs. the standard PFG diffusion technique. Conclusion: CT-D diffusion MRI is a viable alternative to standard PFG-diffusion MRI that produces higher SNR and is less demanding on the imaging gradients. This work could have implications for diffusion MRI microscopy.

15:00 5150. Novel Magnetization-Prepared Multi-Slice Multi-Shot EPI Pulse Sequence for T1rho Quantitation

Eric T. Han¹, Weitian Chen¹, Ajit Shankaranarayanan<sup>1

1</sup>Applied Science Laboratory, GE Healthcare, Menlo Park, CA, United States

There are numerous clinical scenarios where evaluation of T1ñ in a focal region-of-interest is desired. In such cases, a quantitative multi-slice 2D T1ñ approach may be more appropriate and time-efficient than a 3D technique. We propose a novel 2D multi-slice T1ñ imaging sequence that overcomes many of the shortcomings of current multi-slice T1ñ methods. Using this sequence, in vivo T1ñ maps of the knee, spine, and brain are acquired.