title: Detection of different kidney stone types: an ex vivo comparison of ultrashort echo time MRI to reference standard CT.
abstract: OBJECTIVE
  With the development of ultrashort echo time (UTE) sequences, it may now be possible to detect kidney stones by using magnetic resonance imaging (MRI). In this study, kidney stones of varying composition and sizes were imaged using both UTE MRI as well as the reference standard of computed tomography (CT), with different surrounding materials and scan setups.
  
  
  METHODS
  One hundred and fourteen kidney stones were inserted into agarose and urine phantoms and imaged both on a dual-energy CT (DECT) scanner using a standard renal stone imaging protocol and on an MRI scanner using the UTE sequence with both head and body surface coils. A subset of the stones representing all composition types and sizes was then inserted into the collecting system of porcine kidneys and imaged in vitro with both CT and MRI.
  
  
  RESULTS
  All of the stones were visible on both CT and MRI imaging. DECT was capable of differentiating between uric acid and nonuric acid stones. In MRI imaging, the choice of coil and large field of view (FOV) did not affect stone detection or image quality. The MRI images showed good visualization of the stones' shapes, and the stones' dimensions measured from MRI were in good agreement with the actual values (R(2)=0.886, 0.895, and 0.81 in the agarose phantom, urine phantom, and pig kidneys, respectively). The measured T2 relaxation times ranged from 4.2 to 7.5ms, but did not show significant differences among different stone composition types.
  
  
  CONCLUSIONS
  UTE MRI compared favorably with the reference standard CT for imaging stones of different composition types and sizes using body surface coil and large FOV, which suggests potential usefulness of UTE MRI in imaging kidney stones in vivo.
authors.affiliation: Mayo Clinic, 4500 San Pablo Road, Jacksonville, FL 32224, USA; University of Michigan, 1500 East Medical Center Drive, Ann Arbor, MI 48109, USA. Electronic address: elsayei@umich.edu.
authors.forename: El-Sayed H
authors.initials: el-SH
authors.lastname: Ibrahim
authors.affiliation: Mayo Clinic, 4500 San Pablo Road, Jacksonville, FL 32224, USA.
authors.forename: Joseph G
authors.initials: JG
authors.lastname: Cernigliaro
authors.affiliation: Mayo Clinic, 4500 San Pablo Road, Jacksonville, FL 32224, USA.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Pooley
authors.affiliation: Mayo Clinic, 4500 San Pablo Road, Jacksonville, FL 32224, USA.
authors.forename: Mellena D
authors.initials: MD
authors.lastname: Bridges
authors.affiliation: Mayo Clinic, 4500 San Pablo Road, Jacksonville, FL 32224, USA.
authors.forename: Jamie G
authors.initials: JG
authors.lastname: Giesbrandt
authors.affiliation: Indiana University, 340 West 10th Street, Indianapolis, IN 46202, USA.
authors.forename: James C
authors.initials: JC
authors.lastname: Williams
authors.affiliation: Mayo Clinic, 4500 San Pablo Road, Jacksonville, FL 32224, USA.
authors.forename: William E
authors.initials: WE
authors.lastname: Haley
mesh_terms: D000818:Animals; D006801:Humans; D007669:Kidney Calculi / Q000000981:diagnostic imaging* / Q000473:pathology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D019047:Phantoms, Imaging; D012015:Reference Standards; D013552:Swine; D014057:Tomography, X-Ray Computed / Q000379:methods*
keywords: Abdominal CT; Dual-energy computed tomography (DECT); Kidney stone imaging; MRI; Ultrashort echo time