title: Multiresolution MRI temperature monitoring in a reduced field of view.
abstract: OBJECTIVE
  The purpose was to develop a new magnetic resonance imaging technique for fast temperature monitoring with extended volume coverage.
  
  
  METHODS
  The Multiple Resolutions Along Phase-Encode and Slice-Select Dimensions (MURPS) method was implemented in both a two-dimensional (2D) spoiled gradient echo (SPGR) sequence and a multishot echo-planar imaging (EPI) sequence. Both modified sequences were used to acquire image data from three slices with variable phase-encode resolution and slice thickness. In the SPGR sequence, a 2D resonant frequency pulse was also implemented to enable imaging within a reduced field of view, and this was used to monitor (at 1.5 T) the temperature changes in a live rabbit and in gel phantoms heated by focused ultrasound. A modified EPI sequence was tested during heating of a phantom undergoing motion.
  
  
  RESULTS
  The in vivo experiments demonstrated that temperature changes in unexpected locations away from the focal plane, such as near bone structures, could be detected due to the extra volume coverage afforded by the MURPS method. Temperature changes in a moving phantom were resolved using the MURPS EPI sequence with an acquisition rate of three slices every 300 ms.
  
  
  CONCLUSIONS
  The MURPS method enables temperature monitoring over multiple slices without loss of temporal resolution compared with single-slice imaging and, if combined with multishot EPI, enables volume temperature monitoring in moving organs.
authors: Department of Physics, University of Massachusetts Lowell, Lowell, MA, USA.
authors: Mohammed H
authors: MH
authors: Aljallad
authors: Jing
authors: J
authors: Yuan
authors: Magdalini C
authors: MC
authors: Pilatou
authors: Nathan J
authors: NJ
authors: McDannold
authors: Lawrence P
authors: LP
authors: Panych
mesh_terms: D000818:Animals; D017352:Echo-Planar Imaging / Q000379:methods; D004867:Equipment Design; D005782:Gels; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008280:Magnetics; D008297:Male; D015233:Models, Statistical; D019047:Phantoms, Imaging; D011817:Rabbits; D013696:Temperature; D013997:Time Factors; D014463:Ultrasonography / Q000379:methods
chemical_list: D005782:Gels