title: Development of a magnetic resonance imaging protocol to visualize encapsulated contrast agent markers in prostate brachytherapy recipients: initial patient experience.
abstract: OBJECTIVE
  Computed tomography (CT)-based prostate post-implant dosimetry allows for definitive seed localization but is associated with high interobserver variation in prostate contouring. Currently, magnetic resonance imaging (MRI)-based post-implant dosimetry allows for accurate anatomical delineation but is limited due to inconsistent seed localization. Encapsulated contrast agent markers were previously proposed to overcome the seed localization limitation on MRI images by placing hyperintense markers adjacent to hypointense seeds. The aim of this study was to assess the appearance of these markers in prostatic tissue, and develop an MRI protocol to enable marker visualization.
  
  
  METHODS
  We acquired MRI scans in prostate implant patients (n = 10) on day 0 (day of implant) and day 30 (month after implant). Before implantation of the markers, the routine post-implant MRI protocol included a 3D T2-weighted fast-spin-echo (FSE) sequence with which markers and seeds could not be clearly visualized. To visualize the MRI markers, a 3D fast radiofrequency-spoiled gradient-recalled echo (FSPGR) sequence was evaluated for marker and seed visibility, as well as prostate boundary definitions.
  
  
  RESULTS
  The 3D FSPGR sequence allowed for the visualization of markers in the prostate, enabling the distinction of signal voids as seeds versus needle tracks. The updated post-implant MRI protocol consists of this 3D FSPGR scan and an optional 3D T2-weighted FSE scan. The optional 3D T2-weighted FSE sequence may be employed to better visualize intraprostatic detail. We also described the observed image artifacts, including seed susceptibility, marker chemical shift, partial volume averaging, motion, and wraparound artifacts.
  
  
  CONCLUSIONS
  We have demonstrated an MRI protocol for use with hyperintense encapsulated contrast agent markers to assist in the identification of hypointense seeds.
authors: University of Texas at Houston Graduate School of Biomedical Sciences, Houston, TX; Department of Radiation Physics, University of Texas MD Anderson Cancer Center, Houston, TX.
authors: Tze Yee
authors: TY
authors: Lim
authors: Department of Radiation Physics, University of Texas MD Anderson Cancer Center, Houston, TX.
authors: Rajat J
authors: RJ
authors: Kudchadker
authors: Department of Radiation Physics, University of Texas MD Anderson Cancer Center, Houston, TX.
authors: Jihong
authors: J
authors: Wang
authors: Department of Diagnostic Radiology, University of Texas MD Anderson Cancer Center, Houston, TX.
authors: Tharakeswara
authors: T
authors: Bathala
authors: Department of Diagnostic Radiology, University of Texas MD Anderson Cancer Center, Houston, TX.
authors: Janio
authors: J
authors: Szklaruk
authors: Department of Radiation Oncology, University of Texas MD Anderson Cancer Center, Houston, TX, USA.
authors: Thomas J
authors: TJ
authors: Pugh
authors: Department of Radiation Oncology, University of Texas MD Anderson Cancer Center, Houston, TX, USA.
authors: Usama
authors: U
authors: Mahmood
authors: Department of Radiation Physics, University of Texas MD Anderson Cancer Center, Houston, TX.
authors: Geoffrey S
authors: GS
authors: Ibbott
authors: Department of Radiation Oncology, University of Texas MD Anderson Cancer Center, Houston, TX, USA.
authors: Steven J
authors: SJ
authors: Frank
keywords: MRI; brachytherapy; dosimetry markers; prostate cancer; seeds