title: Modified echo peak correction for radial acquisition regime (RADAR).
abstract: OBJECTIVE
  Because radial sampling imposes many limitations on magnetic resonance (MR) imaging hardware, such as on the accuracy of the gradient magnetic field or the homogeneity of B(0), some correction of the echo signal is usually needed before image reconstruction. In our previous study, we developed an echo-peak-shift correction (EPSC) algorithm not easily affected by hardware performance. However, some artifacts remained in lung imaging, where tissue is almost absent, or in cardiac imaging, which is affected by blood flow. In this study, we modified the EPSC algorithm to improve the image quality of the radial aquisition regime (RADAR) and expand its application sequences.
  
  
  METHODS
  We assumed the artifacts were mainly caused by errors in the phase map for EPSC and used a phantom on a 1.5-tesla (T) MR scanner to investigate whether to modify the EPSC algorithm. To evaluate the effectiveness of EPSC, we compared results from T(1)- and T(2)-weighted images of a volunteer's lung region using the current and modified EPSC. We then applied the modified EPSC to RADAR spin echo (SE) and RADAR balanced steady-state acquisition with rewound gradient echo (BASG) sequence.
  
  
  RESULTS
  The modified EPSC reduced phase discontinuity in the reference data used for EPSC and improved visualization of blood vessels in the lungs. Motion and blood flow caused no visible artifacts in the resulting images in either RADAR SE or RADAR BASG sequence.
  
  
  CONCLUSIONS
  Use of the modified EPSC eliminated artifacts caused by signal loss in the reference data for EPSC. In addition, the modified EPSC was applied to RADAR SE and RADAR BASG sequences.
authors.affiliation: Application Development Department, MRI System Division, Hitachi Medical Corporation, Kashiwa, Chiba, Japan. takizawa@rd.hitachi-medical.co.jp
authors.forename: Masahiro
authors.initials: M
authors.lastname: Takizawa
authors.forename: Taeko
authors.initials: T
authors.lastname: Ito
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Itagaki
authors.forename: Tetsuhiko
authors.initials: T
authors.lastname: Takahashi
authors.forename: Kanichirou
authors.initials: K
authors.lastname: Shimizu
authors.forename: Junta
authors.initials: J
authors.lastname: Harada
mesh_terms: D000465:Algorithms; D016477:Artifacts; D006257:Head / Q000033:anatomy & histology; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D007668:Kidney / Q000033:anatomy & histology; D008168:Lung / Q000033:anatomy & histology / Q000098:blood supply / Q000502:physiology; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D009038:Motion; D019047:Phantoms, Imaging; D012039:Regional Blood Flow