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Open Access Publications from the University of California

Scholarly Works (3 results)

  • Thesis
  • Peer Reviewed
UCLA Electronic Theses and Dissertations (2023)

Prostate Cancer (PCa) remains the second most common cause of cancer-related death in men in the U.S. Multi-parametric (mp) MRI is playing an increasingly important role for the localization, detection, and risk stratification of PCa. However, prostate mp-MRI still misses PCa in up to 45% of men and faces challenges in distinguishing clinically significant PCa from indolent PCa. Therefore, MRI technology must be improved to enhance diagnostic performance for PCa. This thesis aimed to improve prostate MRI by addressing two challenges. First, the diffusion-weighted imaging (DWI) component of mp-MRI often suffers from artifacts such as distortion and low signal-to-noise ratio (SNR), which can lead to low diagnostic image quality. Second, prostate microstructure features are key determinants for histopathological assessment of cancer aggressiveness; however, current MRI techniques have limitations in capturing this information. To address the first challenge, in Aim 1, we translated and evaluated an eddy current-nulled convex optimized diffusion encoding (ENCODE) based prostate DWI technique that achieves short echo time (TE) to maintain SNR while reducing prostate geometric distortion from eddy currents and susceptibility effects. Further, in Aim 2, we developed a combined TE-minimized ENCODE diffusion encoding acquisition with a random matrix theory-based denoising reconstruction technique to improve the SNR and robustness of high-resolution (in-plane: 1.0x1.0 mm2) prostate DWI and apparent diffusion coefficient mapping. To address the second challenge, in Aim 3, we performed a first proof-of-concept ex vivo evaluation and validation of the diffusion-relaxation correlation spectrum imaging (DR-CSI) technique at 3T for quantifying microscopic tissue compartments (epithelium, stroma, and lumen) in PCa using whole-mount digital histopathology as the reference standard. Further, in Aim 4, we explored and evaluated sequential backward selection analysis for the acceleration of DR-CSI through subsampling of the diffusion-relaxation contrast encoding space while maintaining the accuracy of prostate microstructure mapping in PCa.

    Cover page: Quantitative Prostate Diffusion MRI and Multi-Dimensional Diffusion-Relaxation Correlation MRI for Characterization of Prostate Cancer
    • Article
    • Peer Reviewed
    UCLA Previously Published Works (2018)
    PURPOSE:To evaluate a technique for simultaneous quantitative T2 and apparent diffusion coefficient (ADC) mapping in the heart (T2 +ADC) using spin echo (SE) diffusion-weighted imaging (DWI). THEORY AND METHODS:T2 maps from T2 +ADC were compared with single-echo SE in phantoms and with T2 -prepared (T2 -prep) balanced steady-state free precession (bSSFP) in healthy volunteers. ADC maps from T2 +ADC were compared with conventional DWI in phantoms and in vivo. T2 +ADC was also demonstrated in a patient with acute myocardial infarction (MI). RESULTS:Phantom T2 values from T2 +ADC were closer to a single-echo SE reference than T2 -prep bSSFP (-2.3 ± 6.0% vs 22.2 ± 16.3%; P < 0.01), and ADC values were in excellent agreement with DWI (0.28 ± 0.4%). In volunteers, myocardial T2 values from T2 +ADC were significantly shorter than T2 -prep bSSFP (35.8 ± 3.1 vs 46.8 ± 3.8 ms; P < 0.01); myocardial ADC was not significantly (N.S.) different between T2 +ADC and conventional motion-compensated DWI (1.39 ± 0.18 vs 1.38 ± 0.18 mm2 /ms; P = N.S.). In the patient, T2 and ADC were both significantly elevated in the infarct compared with remote myocardium (T2 : 40.4 ± 7.6 vs 56.8 ± 22.0; P < 0.01; ADC: 1.47 ± 0.59 vs 1.65 ± 0.65 mm2 /ms; P < 0.01). CONCLUSION:T2 +ADC generated coregistered, free-breathing T2 and ADC maps in healthy volunteers and a patient with acute MI with no cost in accuracy, precision, or scan time compared with DWI. Magn Reson Med 79:654-662, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
      Cover page: Simultaneous measurement of T2 and apparent diffusion coefficient (T2+ADC) in the heart with motion‐compensated spin echo diffusion‐weighted imaging
      • Article
      • Peer Reviewed
      UCLA Previously Published Works (2019)

      Objective

      This investigation was performed to evaluate the registration accuracy between magnetic resonance imaging (MRI) and pathology using three-dimensional (3-D) printed molds.

      Methods

      Tissue-mimicking prostate phantoms were manufactured with embedded fiducials. The fiducials were used to measure and compare target registration error (TRE) between phantoms that were sliced by hand versus phantoms that were sliced within 3-D-printed molds. Subsequently, ten radical prostatectomy specimens were placed inside molds, scanned with MRI, and then sliced. The ex vivo scan was used to assess the true location of whole mount (WM) slides relative to in vivo MRI. The TRE between WM and in vivo MRI was measured using anatomic landmarks.

      Results

      Manually sliced phantoms had a 4.1-mm mean TRE, whereas mold-sliced phantoms had a 1.9-mm mean TRE. Similarly, mold-assisted slicing reduced mean angular misalignment around the left-right (LR) anatomic axis from 10.7° to 4.5°. However, ex vivo MRI revealed that excised prostates were misaligned within molds, including a mean 14° rotation about the LR axis. The mean in-plane TRE was 3.3 mm using molds alone and 2.2 mm after registration was corrected with ex vivo MRI.

      Conclusion

      Patient-specific molds improved accuracy relative to manual slicing techniques in a phantom model. However, the registration accuracy of surgically resected specimens was limited by their imperfect fit within molds. This limitation can be overcome with the addition of ex vivo imaging.

      Significance

      The accuracy of 3-D-printed molds was characterized, quantifying their utility for facilitating MRI-pathology registration.
        Cover page: Registration Accuracy of Patient-Specific, Three-Dimensional-Printed Prostate Molds for Correlating Pathology With Magnetic Resonance Imaging
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