TRADITIONAL POSTER - ismrm

Poster Sessions
ultrasound disruption of the blood-brain barrier in rats. Comparison of captured acoustic emissions with T1w and T2w images demonstrated that the
hydrophone was able to detect differences in acoustic emissions in sonications producing different bioeffects. The results show promise for real-time
monitoring of MRI-guided transcranial therapy.
1800. MR Guided HIFU in Cadaver Breasts for Pre-Operative Tumor Localization of Non-Palpable Breast
Tumors as an Alternative to Needle Wire Tumor Localization
Rachel R. Bitton 1 , Elena Kaye 1,2 , Bruce Daniel 1 , Kim Butts Pauly 1
1 Radiology, Stanford University, Palo Alto, CA, United States; 2 Electrical Engineering, Stanford University, Palo Alto, CA, United
States
Physicians are increasingly confronted with non-palpable breast lesions only visible on MRI. This study examined the visibility and palpability of focused
ultrasound lesions in fatty human breast tissue. Eighteen sonications were made around the perimeter of an arbitrary prescribed “tumor” square, representing
a non-palpable tumor area. Potential stiffness changes were measured using MR-ARFI showing the displacement difference between the pre and post
sonication. The lesions were fully registered with images, circumscribing a tumor area in a human cadaver breast, and thus, providing a visible and palpable
perimeter for a surgeon as a guide for excision during breast conservation surgery.
1801. Detecting Blood-Brain Barrier Disruption Under Biosafety Regime Using Optimum Transcranial
Focused Ultrasound and Improved Contrast-Enhanced MRI
Jun-Cheng Weng 1,2 , Sheng-Kai Wu 3 , Win-Li Lin 3,4 , Wen-Yih Iascc Tseng 1,5
1 Center for Optoelectronic Biomedicine, National Taiwan University College of Medicine, Taipei, Taiwan; 2 Department of Medical
Imaging and Radiological Sciences, Chung Shan Medical University, Taichung, Taiwan; 3 Institute of Biomedical Engineering,
National Taiwan University, Taipei, Taiwan; 4 Medical Engineering Research Division, National Health Research Institutes, Miaoli,
Taiwan; 5 Department of Medical Imaging, National Taiwan University Hospital, Taipei, Taiwan
Focused ultrasound (FUS) along with an ultrasound contrast agent (UCA) can induce transient and local increase in the permeability of blood vessel wall or
cell membrane, and the change in blood-brain barrier (BBB) permeability can be appropriately indicated by contrast-enhanced MRI. Recently, most studies
have used optimum FUS parameters with intravascular injection of pre-formed micro-bubbles to produce BBB disruption with minimum damage to the
neurons. However, there are no studies reporting that under biosafety regime BBB disruption could still be predicted by MR contrast enhancement. The
purpose of this study was to see if the traditional T1-weighted (T1W) imaging sequences, spin echo (SE) and gradient echo (GE), can discern the difference
in the BBB disruption in lower dose regime or not. A high sensitivity R1 mapping was used as a gold standard and absolutely quantification. The
quantitative analysis indexing the degree of BBB disruption and the correlation against Evans blue (EB) staining were also demonstrated. Our results suggest
that, in the absence of hemorrhage, contrast-enhanced T1W gradient echo and spin echo sequence were equally reliable in quantifying the BBB disruption.
1802. Analysis of Focused Ultrasound Hotspot Appearance on EPI and Spiral MR Imaging
Sonal Josan 1 , Andrew B. Holbrook, 12 , Elena Kaye, 1,3 , Christine Law, 1,3 , Kim Butts Pauly 1
1 Radiology, Stanford University, Stanford, CA, United States; 2 Bioengineering, Stanford University, Stanford, CA, United States;
3 Electrical Engineering, Stanford University, Stanford, CA, United States
MR thermometry relies on the proton resonance frequency shift with temperature, which can produce off-resonance artifacts in EPI and spiral sequences.
This work analyzed the appearance of the focused ultrasound (FUS) hotspot on several EPI and Spiral trajectory designs through simulations and FUS
experiments. The distortion of the FUS spot with single shot EPI or Spiral imaging can be severe for the high temperature changes used in ablation, and may
lead to under-estimation of the peak temperature. Multi-shot sequences can be used to reduce the shifts/distortion to a tolerable level.
1803. Preventing Far-Field Bone-Reflection of HIFU Beam by Selective Elements De-Activation Is a Sub-
Optimal Approach
Loredana Baboi 1 , Magalie Viallon 1 , Sylvain Terraz 1 , Thomas Goget 1 , Denis Morel 2 , Christoph Becker 1 ,
Rares Salomir 1
1 Department of Radiology, University Hospital of Geneva, Geneva, Switzerland; 2 Department of Anesthesiology, Pharmacology and
Surgical Intensive Care, University Hospital of Geneva, Geneva, Switzerland
MRgHIFU is a hybrid technology which aims to offer efficient and safe thermal ablation of targeted tumors or other pathological tissues, while preserving
the normal surrounding structures unaltered. Theoretically MRgHIFU has no limitation on lesion size [1]. The main challenge is to avoid near and far field
heating [2]. We demonstrate here that beam reflection on bones is a major problem whenever bone is situated in the proximity of the prescribed region for
sonication, even laterally from the main beam axis. This study evaluates selective de-activation of phased-array transducer’s elements as a potential strategy
to reduce bone reflection.
1804. Simultaneous Acoustic Radiation Force Imaging and PRFS Thermal Monitoring at 3T for MRgHIFU
Focusing
M Viallon 1 , JN Hyacinthe 1 , T Goget 1 , L Baboi 1 , P Gross 2 , CD Becker 1 , R Salomir 1
1 Radiologie, Hopital Universitaire de Genève, Geneva, Switzerland; 2 Siemens Medical Solutions, Erlangen, Germany
One challenge in MRgHIFU is to provide safe and thermally neutral focusing of HIFU beam pattern using acoustic radiation force imaging (ARFI). The
radiation force is localized and highly directional (along the main propagation axis of the HIFU beam) while negligible outside the focal zone. This force
initiates a tissue displacement correlated to the amplitude of the acoustic field and thus a phase shift that can be encoded in the MR signal using a motion
encoding gradient (MEG) [1]. In addition, ARFI also provide ‘stiffness weighted’ images that may allow one to assess for pre- versus post- therapy changes
in tissue. Since HIFU also causes tissue heating, temperature elevation and RFI effects are always associated, at various degree. We propose here to obtain a
precise localization of the HIFU focal point by subtracting GRE phase images from two independent acquisitions, where ARF-induced phase shift is
sequentially encoded with positive and, respectively, negative monopolar MEG pulse. For illustration, the MEG was implemented here along the slice-select
direction.