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Knee Osteoarthritis: gagCEST MR Imaging of Articular Cartilage

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

Abstract Details

2013, Doctor of Philosophy, Ohio State University, Biophysics.
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 in-vivo, 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 MTRasym(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 in-vivo 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 MTRasym(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.
Michael Knopp (Advisor)
Guang Jia (Committee Member)
Michael Tweedle (Committee Member)
107 p.
Biophysics; Radiology

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Citations

  • Wei, W. (2013). Knee Osteoarthritis: gagCEST MR Imaging of Articular Cartilage [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1365247669

    APA Style (7th edition)

  • Wei, Wenbo. Knee Osteoarthritis: gagCEST MR Imaging of Articular Cartilage . 2013. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1365247669.

    MLA Style (8th edition)

  • Wei, Wenbo. "Knee Osteoarthritis: gagCEST MR Imaging of Articular Cartilage ." Doctoral dissertation, Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1365247669

    Chicago Manual of Style (17th edition)

osu1365247669
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This open access ETD is published by The Ohio State University and OhioLINK.