title: Accelerated MRI thermometry by direct estimation of temperature from undersampled k-space data.
abstract: OBJECTIVE
  Acceleration of magnetic resonance (MR) thermometry is desirable for several applications of MR-guided focused ultrasound, such as those requiring greater volume coverage, higher spatial resolution, or higher frame rates.
  
  
  METHODS
  We propose and validate a constrained reconstruction method that estimates focal temperature changes directly from k-space without spatial or temporal regularization. A model comprising fully-sampled baseline images is fit to undersampled k-space data, which removes aliased temperature maps from the solution space. Reconstructed temperature maps are compared to maps reconstructed using parallel imaging (iterative self-consistent parallel imaging reconstruction [SPIRiT]) and conventional hybrid thermometry, and temporally constrained reconstruction thermometry.
  
  
  RESULTS
  Temporal step response simulations demonstrate finer temporal resolution and lower error in 4×-undersampled radial k-space reconstructions compared to temporally constrained reconstruction. Simulations show that the k-space method can achieve higher accelerations with multiple receive coils. Phantom heating experiments further demonstrate the algorithm's advantage over reconstructions relying on parallel imaging alone to overcome undersampling artifacts. In vivo model error comparisons show the algorithm achieves low temperature error at higher acceleration factors (up to 32× with a radial trajectory) than compared reconstructions.
  
  
  CONCLUSIONS
  High acceleration factors can be achieved using the proposed temperature reconstruction algorithm, without sacrificing temporal resolution or accuracy.
authors.affiliation: Institute of Imaging Science, Vanderbilt University, Nashville, Tennessee, USA; Department of Chemical and Physical Biology, Vanderbilt University, Nashville, Tennessee, USA.
authors.forename: Pooja
authors.initials: P
authors.lastname: Gaur
authors.forename: William A
authors.initials: WA
authors.lastname: Grissom
mesh_terms: D000465:Algorithms; D002675:Child, Preschool; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D053783:Magnetic Resonance Imaging, Interventional / Q000379:methods*; D019047:Phantoms, Imaging; D062125:Thermometry / Q000379:methods*; D013997:Time Factors; D059708:Ultrasonic Surgical Procedures
keywords: high-intensity focused ultrasound; image reconstruction; magnetic resonance imaging-guided focused ultrasound; non-Cartesian imaging; parallel imaging; temperature imaging