title: Imaging temperature changes in an interventional 0.5 T magnet: in-vitro results.
abstract: OBJECTIVE
  To evaluate the ability of monitoring laser induced temperature changes in an open, interventional 0.5 T magnet, adopting fast T1-weighted sequences.
  
  
  METHODS
  A fast gradient echo- (FGRE) and a fast spoiled gradient echo-sequence (FSPGR), both enabling an image update every 2.5 s, were investigated for their ability to visualize laser tissue effects at 5 Watt. Laser induced temperature was fluorooptically measured and correlated with signal intensity (SI) changes depicted by magnetic resonance imaging (MRI). MRI-lesions were compared with macroscopic findings.
  
  
  RESULTS
  SI changes on FGRE images appeared as early as 15 s following the onset of laser application and were significantly more pronounced than those seen on FSPGR images (p < .0001). A correlation of r = 0.94 (FGRE) and r = 0.92 (FSPGR) between temperature and SI loss was established. Owing to a steeper slope, the FGRE sequence was considered more sensitive to temperature changes. The areas of macroscopic tissue change correlated with those of SI loss, but lesion size was generally underestimated by MRI.
  
  
  CONCLUSIONS
  Laser monitoring is possible with rapid image updates in a midfield (0.5 T) interventional MRI environment using fast gradient echo sequence designs.
authors.affiliation: Department of Radiology, University Hospital Zurich, Switzerland.
authors.forename: P
authors.initials: P
authors.lastname: Steiner
authors.forename: A W
authors.initials: AW
authors.lastname: Schoenenberger
authors.forename: P
authors.initials: P
authors.lastname: Erhart
authors.forename: E
authors.initials: E
authors.lastname: Penner
authors.forename: G K
authors.initials: GK
authors.lastname: von Schulthess
authors.forename: J F
authors.initials: JF
authors.lastname: Debatin
mesh_terms: D000818:Animals; D066298:In Vitro Techniques; D053685:Laser Therapy / Q000009:adverse effects*; D007834:Lasers / Q000009:adverse effects*; D008099:Liver / Q000473:pathology / Q000528:radiation effects; D008279:Magnetic Resonance Imaging / Q000379:methods; D008991:Monitoring, Physiologic / Q000379:methods*; D019047:Phantoms, Imaging; D012680:Sensitivity and Specificity; D013552:Swine; D013696:Temperature