The aim of the study is to develop and implement novel MR sequences that decrease metallic susceptibility artifact about orthopedic hardware, specifically, total hip arthroplasties (THA). TH metal distorts magnetic field and leads to areas in MR images that are black, and obscure underlying tissue. Other areas appear bright (signal pile up), and are difficult to distinguish fro pathology.
In Aim 1, we develop a novel pulse sequence that decreases metallic artifact and allows signal acquisition from short T2 tissues (those black on all clinical MR images). They are black because protons relax before the MR can switch from transmit (proton excitation), to receive (signal collection). Short T2 tissue signal can be accessed with a pulse sequence allowing near immediate signal acquisition after proton excitation (Ultrashort echo time (UTE) MRI). We developed UTE-MSI (Ultrashort Echo Time - Multi-spectral Imaging) with a single published article describing it. It uses a 3D acquisition to allow multiplanar reconstruction, a technique called Multi-spectral imaging to decrease metal artifact, and UTE to visualize short T2 tissues. This sequence suffers from long imaging time.
In aim 1, we further develop UTE-MSI sequence, optimize it for improved suppression of metal artifact, better contrast and use a technique called compressed sensing to decrease imaging times. This sequence is UTE-MuSIC (Ultrashort Time to Echo - Multi-Spectral Imaging with Compressed Sensing). Also in aim 1, we compare UTE-MuSIC to a clinical sequence and a well-accepted research sequence (limited distribution to test sites only) that decrease metal artifact. This allows evalution of UTE-MuSIC as compared to standard of care, and best case scenario in research setting. We have developed both qualitative and quantitative methods to compare sequences and will do so in phantoms with metal.
In Aim 2, UTE-MuSIC will be compared to clinical and research sequences to quantitatively evaluate fluid collections with varying concentrations of metal ion using techniques from Aim 1. If successful, fluid collections with metal ion could be identified non-invasively. A well-described complication of Metal-on-Metal (MoM) THA is pseudotumor development that contains metal ions and is destructive to soft tissues (tendon). Also in Aim 2, we will compare the ability of UTE-MuSIC sequence to characterize normal and pathologic tendon in phantoms with metal, simulating potential tendon damage in vivo in the setting of pseudotumor.
In Aim 3, MRI of patients with MoM THA will be done. The San Diego VA Department of Orthopedics sees 30 to 50 MoM patients/year. Patients will be screened for MR eligibility (standard practice), and patients being followed for MoM THA (n=30) will be recruited for longitudinal MR studies in years 2-4 of the grant. In the MoM cohort, at yearly visits, serum ion levels will be checked. In the presence of peri-prosthetic fluid collections, fluid analysis wil be performed. If revision arthroplasty is indicated from a clinical standpoint, joint tissue and prostheses will be evaluated. Tissue will undergo histological evaluation and grading.
The purpose of this study is to develop and implement novel MR sequences that will decrease metallic susceptibility artifact around orthopedic hardware, specifically total hip arthroplasties (THA), allowing non-invasive evaluation of potential complications. Initial sequence development and optimization will be carried out in phantoms, and cadaveric donors. Grading systems will be developed to assess degree of artifact. Techniques will be used to assess pseudotumors characteristic of certain types of THA failure to non-invasively diagnose potential complications. Techniques will be implemented in THA patients. These techniques have far reaching implications for evaluation of Veterans with any metallic hardware, or injuries with shrapnel or bullet fragments.