3D MR technique speeds exam, diagnosis
Multiplanar vastly undersampled isotropic projection steady-state free precession (VIPR-SSFP) MR images obtained following a single five-minute acquisition have similar sensitivity, specificity, and accuracy, as does a routine MR protocol, for helping detect cartilage lesions, anterior and posterior cruciate ligament tears, medial meniscal tears, and medial and lateral collateral ligament tears in the knee, according to a study published in this month's issue of Radiology.
"VIPR-SSFP combines a balanced SSFP technique with a three-dimensional radial k-space acquisition to produce isotropic resolution images of the knee with T2-/T1-weighted contrast," wrote the authors of a retrospective study conducted at the University of Wisconsin Hospital, Clinical Science Center in Madison, Wisc.
The radial acquisition, the authors noted, allows for a rather efficient k-space trajectory in which two radial lines are collected for each repetition time in orientations dispersed throughout a sphere in k-space. The most striking benefit of the technique is that unlike Cartesian methods, VIPR-SSFP does not require phase, section encoding, or dephasing gradients, allowing for almost continuous acquisition of data.
"Multiplanar water separated VIPR-SSFP images of the knee, with 0.5x0.5-mm in-plane spatial resolution and 1.5-mm section thickness, can be produced in a single 5-minute acquisition at 1.5 T and can provide excellent tissue contrast between joint structures," the authors noted.
The Wisconsin-based researchers put the protocol to the test between June 2005 and July 2006 enrolling 292 symptomatic patients who underwent a routine MRI and a VIPR-SSFP to help provide comprehensive knee joint assessment. Of this cohort, 95 patients underwent arthroscopic knee surgery-these patients formed the study group that compared VIPR-SSFP and a routine MRI protocol for evaluating the cartilage, ligaments, menisci, and osseous structures of the knee in symptomatic patients
All patients in the study group had their MR exams performed on the same 1.5T system (Sigma HDx, GE Healthcare) with an eight-channel phased-array extremity coil (Precision Eight TX/TR High Resolution Knee Array, In Vivo). Arthroscopic knee surgery was performed in all 95 patients in the study group within 2 months of their MR study.
The MR images of these patients were reviewed by two radiologists unaware of the arthroscopic findings of each patient. The radiologists first reviewed and interpreted the routine MRI studies, then reviewed and interpreted the VIPR-SSFP sequences. By using arthroscopy as the reference standard, the sensitivity, specificity, and accuracy of VIPR-SSFP and the routine MR protocol for helping detect all grades of cartilage lesions as well as ACL tears, PCL tears, and medial and lateral meniscal tears in the knee were calculated for both readers combined and all surfaces combined.
"VIPR-SSFP had similar sensitivity and accuracy and significantly higher specificity than did the routine MR protocol for helping detect surgically confirmed cartilage lesions," the authors reported. "VIPR-SSFP also had similar accuracy, as did the routine MR protocol for correctly helping to grade cartilage lesions."
They noted that the technique, in their research, was less sensitive than conventional MRI at helping detect lateral meniscal tears and bone marrow edema lesions.
Although VIPR-SSFP looks to be promising, the authors cautioned that the technique requires further technical development before it can replace currently used routine MR knee protocols. However, there may be some instances where it is appropriate to utilize the technique.
"VIPR-SSFP may be used to provide rapid comprehensive knee joint assessment for patients with severe pain or claustrophobia who cannot tolerate a 25-minute routine MR examination," the researchers wrote. "VIPR-SSFP may also be combined with other sequences in a rapid, cost-effective clinical MR protocol and can be used in osteoarthritis research studies to provide rapid cartilage volume analysis and "whole-organ" assessment of the osteoarthritic knee joint."
"VIPR-SSFP combines a balanced SSFP technique with a three-dimensional radial k-space acquisition to produce isotropic resolution images of the knee with T2-/T1-weighted contrast," wrote the authors of a retrospective study conducted at the University of Wisconsin Hospital, Clinical Science Center in Madison, Wisc.
The radial acquisition, the authors noted, allows for a rather efficient k-space trajectory in which two radial lines are collected for each repetition time in orientations dispersed throughout a sphere in k-space. The most striking benefit of the technique is that unlike Cartesian methods, VIPR-SSFP does not require phase, section encoding, or dephasing gradients, allowing for almost continuous acquisition of data.
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| Sagittal MR images of knee in 38-year-old man show surgically confirmed grade 2B cartilage lesion on medial femoral condyle detected by both readers by using VIPR-SSFP and by neither reader by using routine MR. (A) Fat-suppressed T2-weighted fast spin echo image shows subtle irregularity of articular cartilage on medial femoral condyle (arrow). (B) Corresponding VIPR-SSFP image shows focal partial-thickness cartilage lesion on medial femoral condyle (arrow). Image and caption courtesy of the Radiological Society of North America. |
The Wisconsin-based researchers put the protocol to the test between June 2005 and July 2006 enrolling 292 symptomatic patients who underwent a routine MRI and a VIPR-SSFP to help provide comprehensive knee joint assessment. Of this cohort, 95 patients underwent arthroscopic knee surgery-these patients formed the study group that compared VIPR-SSFP and a routine MRI protocol for evaluating the cartilage, ligaments, menisci, and osseous structures of the knee in symptomatic patients
All patients in the study group had their MR exams performed on the same 1.5T system (Sigma HDx, GE Healthcare) with an eight-channel phased-array extremity coil (Precision Eight TX/TR High Resolution Knee Array, In Vivo). Arthroscopic knee surgery was performed in all 95 patients in the study group within 2 months of their MR study.
The MR images of these patients were reviewed by two radiologists unaware of the arthroscopic findings of each patient. The radiologists first reviewed and interpreted the routine MRI studies, then reviewed and interpreted the VIPR-SSFP sequences. By using arthroscopy as the reference standard, the sensitivity, specificity, and accuracy of VIPR-SSFP and the routine MR protocol for helping detect all grades of cartilage lesions as well as ACL tears, PCL tears, and medial and lateral meniscal tears in the knee were calculated for both readers combined and all surfaces combined.
"VIPR-SSFP had similar sensitivity and accuracy and significantly higher specificity than did the routine MR protocol for helping detect surgically confirmed cartilage lesions," the authors reported. "VIPR-SSFP also had similar accuracy, as did the routine MR protocol for correctly helping to grade cartilage lesions."
They noted that the technique, in their research, was less sensitive than conventional MRI at helping detect lateral meniscal tears and bone marrow edema lesions.
Although VIPR-SSFP looks to be promising, the authors cautioned that the technique requires further technical development before it can replace currently used routine MR knee protocols. However, there may be some instances where it is appropriate to utilize the technique.
"VIPR-SSFP may be used to provide rapid comprehensive knee joint assessment for patients with severe pain or claustrophobia who cannot tolerate a 25-minute routine MR examination," the researchers wrote. "VIPR-SSFP may also be combined with other sequences in a rapid, cost-effective clinical MR protocol and can be used in osteoarthritis research studies to provide rapid cartilage volume analysis and "whole-organ" assessment of the osteoarthritic knee joint."