Knee Osteoarthritis: gagCEST MR Imaging of Articular Cartilage

Knee osteoarthritis (OA) is a public health problem that involves the disorder of articular cartilage. Until now, there is no effective cure for it. However, beginning treatments and therapies at an early stage can help in preventing further disease progression.It has been reported that the loss of glycosaminoglycan (GAG) in cartilage is a signal of early OA onset. Magnetic resonance imaging (MRI) is a clinical imaging technique commonly detecting the signals from water and labile protons. The macromolecules such as GAGs have much shorter echo time and are not able to be identified using conventional MRI techniques. In order to monitor GAG concentration change <i>in-vivo</i>, an indirect way of measurement is needed to be found. Based on the chemical exchange effect between GAG hydroxyl protons and free water protons, gagCEST MRI was developed as a molecular imaging methodology aiming at the GAG molecules in the body parts such as cartilage and intervertebral disc. With the purpose of setting up the CEST sequences, phantom scans were performed. The MR signals under saturation pulses at different frequencies were fit into a smooth CEST spectrum and MTR asymmetry curve were calculated. High MTR_asym(1.0 ppm) values reflect the macromolecular contents such as proteins in eggs and glucose in cantaloupe. The general frame of pre-saturation pulse was set up as a series of sixteen block pulses.The quantitation of CEST MRI is based on the asymmetry in the CEST spectrum curve around 1.0 ppm where hydroxyl protons resonate and its reference frequency -1.0 ppm. Because the hydroxyl group resonance frequency is similar to that of water, it makes gagCEST MRI very sensitive to B₀ field inhomogeneity. Conventionally, an entire CEST spectrum with high spectral resolution is sampled to match the actual minimum signal with the water frequency. This will give rise to a long acquisition time and prevent it from reaching clinical use. To deal with this problem, a dual gradient echo B₀ map based on the phase evolution during the interval echo time is used to find the field inhomogeneity. With both phantom and <i>in-vivo</i> tests, it is demonstrated that with proper interval echo time, the dual gradient echo B₀ map is able to make reliable B₀ inhomogeneity correction to CEST spectra. The clinical imaging for healthy volunteers and knee patients has been performed. Significant higher MTR_asym(1.0 ppm) in healthy volunteers than in OA patients was seen which proved gagCEST MRI having the potential to detect and quantify GAG loss in OA patients. gagCEST MRI can help in clinical treatment planning a therapy assessment. The comparison with the gold standard delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) was made on twelve college football athletes who has been reported to have higher prevalence of cartilage lesions than the general population. gagCEST correlates well with dGEMRIC in evaluating relatively higher GAG concentrations. However, when it comes to lower GAG concentrations, dGEMRIC has better sensitivity and accuracy in differentiating various GAG levels.

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Biophysics

Grantor dc:publisher

The Ohio State University

Year dc:date

2013

Author dc:creator

• Wei, Wenbo

Contributors dc:contributor

• Knopp, Michael

• Biophysics
• Radiology

Statement dc:rights

• unrestricted
• This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws.

Language dc:language

English

Repository record dc:identifier

http://rave.ohiolink.edu/etdc/view?acc_num=osu1365247669

OAI identifier oai:identifier

oai:etd.ohiolink.edu:osu1365247669