Shiyang Wang PhD, Presenter: Grant, Koninklijke Philips NV

Aytekin Oto MD, Abstract Co-Author: Research Grant, Koninklijke Philips NV Consultant, Guerbet SA

Steffen Sammet MD, PhD, Abstract Co-Author: Research Grant, Koninklijke Philips NV

Weiwei Du, Abstract Co-Author: Nothing to Disclose

Milica Medved PhD, Abstract Co-Author: Nothing to Disclose

Gregory Stanislaus Karczmar PhD, Abstract Co-Author: Nothing to Disclose

Ambereen Yousuf MBBS, Abstract Co-Author: Nothing to Disclose

Jianing Wang, Abstract Co-Author: Nothing to Disclose

MRI-guided laser ablation is becoming an important option for men with low-grade prostate cancer (PCa). However, improvements in imaging to guide ablation are needed. Contrast enhanced MRI cannot be used to evaluate lesions between ablations for the effect of heating on the stability of the contrast agent. Therefore we are testing use of multi-gradient echo (MGE) MRI to identify ablation zones and characterize effect of each ablation without contrast media injection. Data from MGE MRI were analyzed in the time domain to detect changes in water resonance peak height, frequency, and other characteristics that may be sensitive to cancer and changes produced by ablation, including hypoxia, hemorrhage, and edema.

Five biopsy proven PCa patients were studied with IRB approval. MGE MRI was acquired in axial plane with free breathing (Philips 3T Achieva). Twenty echoes were acquired with ΔTE=3.2ms; resolution=2.30/2.3/3.8 mm; TR=1.7s, 23 slices; scan time 1.8 minutes. Five cancer and five normal ROIs were outlined by an experienced radiologist. The proton free induction decay in each voxel was Fourier transformed, the water resonance peak height (WPH) was measured and T2*map was calculated. Statistical significance was evaluated with two-way student t-test.

The average post-ablation water peak height decreased significantly compared with pre-ablation in cancer ROIs (p=0.029). T2* in lesions post-ablation was significantly shorter than T2* in normal ROIs (p=0.002). The ratio of WPH in normal tissue to WPH in cancer changes significantly after ablation (p<0.05) and the same is true for T2*. Fig.1 A-B compares a post-ablation MGE image (TE=64.6ms) with a T1WI after contrast media injection. Figure 1C shows the difference between WPH images acquired pre- and post- ablation, and Fig.1 D shows the difference between T2*maps acquired pre- and post-ablation.

MGE MRI shows the ablation zone without the need of contrast injection. This allows repeated assessment following each heating period so that subsequent ablations can be optimized. In addition, changes in the water resonance lineshape or resonance frequency may provide information concerning effects of MRI-guided laser ablation.

MGE MRI can provide useful information regarding the effect of ablation without contrast agent injection. This allows intra-treatment monitoring and optimization of the laser focal therapy procedure.

Wang, S, Oto, A, Sammet, S, Du, W, Medved, M, Karczmar, G, Yousuf, A, Wang, J, Ablation Zone Identification Using Multi-Gradient Echo MRI in Laser Focal Therapy for Prostate Cancer.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14045419.html