Multi-parametric MRI (MP-MRI) in prostate- Experience and Technical Challenges

Transcription

1 Multi-parametric MRI (MP-MRI) in prostate- Experience and Technical Challenges Award: Radiographer Award Poster No.: C-0402 Congress: ECR 2018 Type: Educational Exhibit Authors: R. Lee, G. Lo, K. F. Chan, C. T. Yuen, K. M. Chan, M. C. W Liu, P. L. P. Chan ; Hong Kong/CN, Happy Valley/CN, HONG KONG/HK Keywords: Cancer, Technical aspects, Imaging sequences, MR, Urinary Tract / Bladder, Pelvis DOI: /ecr2018/C-0402 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 30

2 Learning objectives The purpose of exhibition is through cases, illustrations and pictures to review the technical factors and challenges in performing Multiparametric MRI (MP-MRI) in prostate. Understand the state-of-the-art MP-MRI techniques (eg. Diffusion,DCE) and protocol optimization enabling effective MP-MRI examination in detection and localization of prostate cancer Highlight the possible means to tackle the challenges and discuss the future development (eg PET/MRI) in MP-MRI of prostate Page 2 of 30

3 Background Prostate cancer (PCa) is the most common non-cutaneous cancer in men. Multiparametric magnetic resonance imaging (MP-MRI) Fig.1, is an important diagnostic tool in detecting and localizing prostate pathology. It includes anatomical (T2-weighted) imaging, and functional MRI techniques such as diffusion weighted (DW) imaging, dynamic contrast-enhanced (DCE) imaging, and MR spectroscopic imaging to improve the sensitivity and specificity in cancer detection. Innovations in hardware and software in last decade have significantly improved image quality, e.g., the use of 3 Tesla MR scanner, higher channel phase array coil, and computed high b-value diffusion-weighted imaging (c-dwi). However, proper MR imaging techniques and protocol optimization are necessary to enable effective MP-MRI examination in detection and localization of prostate cancer. Page 3 of 30

4 Images for this section: Fig. 1: Multiparametric MRI pulse sequences including T1, T2, DWI, DCE and spectroscopy (optional) Page 4 of 30

5 Fig. 2: MRI has better contrast resolution than CT in prostate imaging. Page 5 of 30

6 Findings and procedure details Anatomy The superior part of the prostate is called the base and the most inferior part is the apex. The prostate consists of 3 distinct zones (Fig.3): 1) the peripheral zone, located posteriorly and caudally at its middle portion; 2) the transition zone, located interiorly, around the urethra; 3) the central zone, which is posterior and superior to the transition zone. The peripheral zone accounts for approximately 70% of the total prostate volume in a young adult. The peripheral zone surrounds the distal urethra at the apex of the prostate and extends posterolaterally to the base. The peripheral zone is deficient anteriorly. This area is filled by the anterior fibromuscular stroma. The central zone takes up 25% of the prostate volume and contains the ejaculatory ducts. The transition zone takes up the remaining 5%. It is predominantly anterolateral to proximal urethra. However, in the aging man, owing to variable extension of the transition zone due to benign prostatic hyperplasia, the size and MR signal intensity may vary and the remaining compressed central zone is often indefinable on MR images. Hardware considerations 1-2 decades ago, the coil of choice for high quality MR prosate imaging at 1.5T was typically an endorectal coil (Fig. 4). This allowed placing the coil close to the prostate, providing higher signal-to-noise ratio (SNR) than was possible with pelvic array coils at the time. The increased SNR allows to obtain higher resolution imaging for prostate than using pelvic array coil. The small size of this coil however has the disadvantage of reduced signal penetration to the anatomy further from prostate resulting in poor or no visualization for the rest of pelvic structures. With the advancement of multichannel phase-array pelvic coil, recent coil setup for scanning prostate includes Endorectal coil combining with pelvic phased-array coil in 1.5 Tesla MR system Using pelvic phased-arrary coil only in 3 Tesla MR system because of higher signal-to-noise ratio (Fig. 5 & Fig 6). Page 6 of 30

7 Use of endorectal coil is less preferable as there are disadvantages of patient discomfort, motion artifact, increasing cost, time of setup and distortion of prostate shape. Protocol and role of MP-MRI sequences Figure 7 illustrated the MP-MRI sequences adopted T1 weighted images has poor contrast resolution for zonal anatomy, however, it is good to localize area of post-biopsy hemorrhage (Fig. 8) that may affect the accuracy of diagnosis. High resolution T2-weighed in 3 planes are need for anatomical and to evaluate zonal anatomy and to determine the presence of extra-prostatic extension (Fig 1a, 1c). Normal peripheral zone presented with intermediateto high-signal-intensity and central/transition zones with low-signal-intensity. However, peripheral zone low signal may not always represent cancer as benign abnormalities such as chronic prostatitis may also presented with low signal. DWI generates image contrast based on differences in water diffusion. In theory, grade of prostate cancer increases cellularity and thus reduce the ability of water to diffuse and resulted in restricted diffusion. Studies have shown improved tumor detection using high b-values or computed high bvalue (Fig. 9) in the range of While the interpretation of DWI is subjective, the restriction of water molecules can be quantified by generating ADC maps and measuring ADC values (mm /s). Angiogenesis in prostate cancer tissue is induced by secretion of vascular growth factors as a result of local hypoxia or lack of nutrients. This changes can be studied with dynamic contrast-enhanced (DCE)MRI. Complementary with T2 and DWI images for early contrast wash-in to detect PCa (Fig. 10). MR Spectroscopy provides additional specificity for PCa detection in terms of metabolic information (e.g. increase choline and reduced citrate level). However, there is a general trend of MR spectroscopy in prostate is predominantly reserved for experimental examinations. Spectroscopy is not suggested in PI-RADS version 2, 2015 for poor sensitivity (16%) and long acquisition time. Common Technical Challenges and Suggested Solutions Motion MP-MRI prostate is a relatively lengthy examination and prone to motion artifact. Artifacts originated from voluntary (e.g. breathing) and involuntary motions are common. Motion of prostate surrounding structures (bladder, rectum, and small bowels) may potentially degrade image quality. Motion artifacts can also be more significant with placement of Page 7 of 30

8 endorectal prostate coil. Figure 11 tabulated the most common sources of patient-related motion, e.g. peristalsis (Fig.12 & Fig.13). The suggested solutions are listed as follows: Ensure patient is relaxed and procedure well explained Antispasmodic medication, e.g. Buscopan & proper coil placement (Fig.13) Faster sequence (e.g. Parallel Imaging) Motion less sensitive sequence (Radial sampling, eg BLADE, PROPELLER) Phase encoding direction (Fig. 14) for Ax (R to L), Sag & Cor (S to I) Empty bladder, patient void prior to exam Monitored anesthesia care - for extremely claustrophobic & uncooperative patients Susceptibility Susceptibility artifacts occur near the interfaces of materials of different magnetic susceptibility, such as bone-soft tissue or air-tissue interfaces, as the result of microscopic gradients or frequency shifts. The artifacts that result from these local magnetic field inhomogeneities are spatial displacements of several pixels (i.e., image distortion) and/or signal dropout. Susceptibility artifact is more vulnerable in 3 Tesla MRI and single shot EPI DWI sequence. Figure 15 summarized the common causes of susceptibility artifact and the suggested solutions are listed as follows: Ensure placing the anatomy of interest (prostate) at the isocenter of the magnet. Deflation of rectal air by placement of rectal catheter just before MRI examination may reduce image distortion (Fig. 16). Use less susceptibility sensitive sequence such as RESOLVE, Readoutsegmented, multi-shot EPI. Increase the bandwidth and shorten the echo time (Fig. 17). Apply local shim. Hemorrhage within 1 week may cause of T2 low signal intensity (Fig. 18) and affect prostate CA detection. Thus, it is recommended performing prostate MRI at least 4-6 weeks after biopsy. Future development Integrated PET/MRI is an emerging technological advancement by combining the 68 excellent anatomic/functional information of MP-MRI and metabolic data from GaPSMA-PET with increased diagnostic accuracy and confidence. PET/MR enhances the staging of metastatic disease (Fig. 19) such prostate bone (Fig. 20) and lymph node metastases (Fig 21). Technological challenges including MR attenuation correction and relatively long acquisition time. Improving software and hardware such as array coil Page 8 of 30

9 technology, MR attenuation correction maps and multiparametric sequences will further enhance the use of PET/MRI as a preferred imaging tool for PCa. Page 9 of 30

10 Images for this section: Fig. 3: Prostate anatomy Page 10 of 30

11 Fig. 4: Endorectal coil positioning with air inflated Fig. 5: Phase Array Coil (3T) versus Combined Endorectal + Phase array coil (1.5T) of same patient showing CA prostate Page 11 of 30

12 Fig. 6: 3T MRI Scanner (Higher S/N) better delineate prostatitis than using 1.5T MRI Scanner by using pelvic phase array coil Page 12 of 30

13 Fig. 7: Prostate Protocol using 3T Pelvic Array Coil Page 13 of 30

14 Fig. 8: Prostate Hemorrhage after Biopsy Complicates Cancer Detection Page 14 of 30

15 Fig. 1: Multiparametric MRI pulse sequences including T1, T2, DWI, DCE and spectroscopy (optional) Page 15 of 30

16 Fig. 9: Computed high-b-value DWI improves sensitivity and conspicuity in Pca detection Page 16 of 30

17 Fig. 10: Patient with Prostate CA in Peripheral and Transition zone. Dynamic Contrast Enhancement with rapid wash-in and wash-out curve Page 17 of 30

18 Fig. 11: Common Technical Challenges: Motion Page 18 of 30

19 Fig. 12: T1 dynamic sequence shows peristalsis of rectum which may cause motion artifact in MP-MRI Page 19 of 30

20 Fig. 13: Motion artifact with blurred prostate Page 20 of 30

21 Fig. 14: Use left-right as phase encoding to avoid breathing artifact Page 21 of 30

22 Fig. 15: Common Technical Challenges: Susceptibility Page 22 of 30

23 Fig. 16: Rectal air deflation before MRI exam may help to reduce susceptibility artifact Page 23 of 30

24 Fig. 17: Susceptibility artifact limits evaluation on T1 & T2. DWI sequence is more sensitive to this artifact that increases with TE Page 24 of 30

25 Fig. 18: T1 image shows bright signal after biopsy representing hemorrhage with heterogeneous signal in T2 that may hamper prostate CA detection Page 25 of 30

26 Fig. 19: Prostate CA in left peripheral & transitional zone with extensive bone metastases Page 26 of 30

27 Fig. 20: MP-MRI detects prostate CA and pubic bone metastasis compared to PSMAPET/MR Page 27 of 30

28 Fig. 21: Prostate CA with lymph node metastases, PET-MR shows superiority in depicting abnormal lymph nodes. Page 28 of 30

29 Conclusion MP-MRI prostate provides high quality anatomic and functional images that improve the diagnosis of PCa. Both radiologists' and radiographers' experience and understanding of MP-MRI technique, are crucial to achieve the best results for detection of prostate carcinoma and relevant pathologies. Page 29 of 30

30 References 1. Barentsz JO, Richenberg J, Clements R, Choyke P, Verma S, Villeirs G, Rouviere O, Logager V, Fütterer JJ; ESUR prostate MR guidelines Eur Radiol Apr;22(4): Barentsz et al. Synopsis of the PI-RADS v2 Guidelines for Multiparametric Prostate Magnetic Resonance Imaging and Recommendations for Use. European Urology : Cabarrus et al. Multiparametric magnetic resonance imaging of the prostatea basic tutorial.translational Andrology and Urology. 2017;6 (3): Hambrock T, Hoeks C, Hulsbergen-van de Kaa C, Scheenen T, Fütterer J, Bouwense S, van Oort I, Schröder F, Huisman H, Barentsz J. Prospective assessment of prostate cancer aggressiveness using 3-T diffusionweighted magnetic resonance imaging-guided biopsies versus a systematic 10-core transrectal ultrasound prostate biopsy cohort. Eur Urol Jan;61(1): Hoeks CM, Barentsz JO, Hambrock T, Yakar D, Somford DM, Heijmink SW, Scheenen TW, Vos PC, Huisman H, van Oort IM, Witjes JA, Heerschap A, Fütterer JJ. Prostate cancer: multiparametric MR imaging for detection, localization, and staging. Radiology Oct;261(1): Review. 6. Liza Lindenberg, Mark Ahlman, Baris Turkbey, Esther Mena, and Peter Choyke. Evaluation of Prostate Cancer with PET/MRI. J Nucl Med 2016; 57:111S-116S 7. Weinreb et al, PI-RADS Prostate Imaging-Reporting and Data System: 2015, Version 2. European Urology : Verma et al. Overview of Dynamic Contrast-Enhanced MRI in Prostate Cancer Diagnosis and Management. American Journal of Roentgenology : Verma et al. Evaluation of the impact of computed high b-value diffusionweighted imaging on prostate cancer detection. Abdom Radiol 2016; 41 (5): Vural et al. Conspicuity of Peripheral Zone Prostate Cancer on Computed Diffusion-Weighted Imaging: Comparison of cdwi1500, cdwi2000, and cdwi3000. BioMed Research International Volume 2014, Article ID Page 30 of 30