title: Evaluation of the keyhole technique applied to the proton resonance frequency method for magnetic resonance temperature imaging.
abstract: OBJECTIVE
  To evaluate the temporal and spatial resolution of magnetic resonance (MR) temperature imaging when using the proton resonance frequency (PRF) method combined with the keyhole technique.
  
  
  METHODS
  Tissue-mimicking phantom and swine muscle tissue were microwave-heated by a coaxial slot antenna. For the sake of MR hardware safety, MR images were sequentially acquired after heating the subjects using a spoiled gradient (SPGR) pulse sequence. Reference raw (k-space) data were collected before heating the subjects. Keyhole temperature images were reconstructed from full k-space data synthesized by combining the peripheral phase-encoding part of the reference raw data and the center phase-encoding keyhole part of the time sequential raw data. Each keyhole image was analyzed with thermal error, and the signal-to-noise ratio (SNR) was compared with the self-reference (nonkeyhole) images according to the number of keyhole phase-encoding (keyhole-data size) portions.
  
  
  RESULTS
  In applied keyhole temperature images, smaller keyhole-data sizes led to more temperature error increases, but the SNR did not decreased comparably. Additionally, keyhole images with a keyhole-data size of <16 had significantly different temperatures compared with fully phase-encoded self-reference images (P < 0.05).
  
  
  CONCLUSIONS
  The keyhole technique combined with the PRF method improves temporal resolution and SNR in the measurement of the temperature in the deeper parts of body in real time.
authors: Department of Biomedical Engineering, Inje University, Gimhae, Gyeongnam, South Korea.
authors: YongHee
authors: Y
authors: Han
authors: ChiWoong
authors: C
authors: Mun
mesh_terms: D000465:Algorithms; D004867:Equipment Design; D005782:Gels; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D015233:Models, Statistical; D009068:Movement; D019047:Phantoms, Imaging; D011522:Protons; D012685:Sepharose / Q000737:chemistry; D013696:Temperature; D013997:Time Factors
chemical_list: D005782:Gels; D011522:Protons; D012685:Sepharose