Rectal Cancer High Res MRI_GinaBrown.pptx

Author: Gina Brown
To guide radiologists and radiographers on how to perform high-resolution MRI for accurate staging of rectal cancer, emphasizing technique, image quality, to ensure sufficient image quality for accurate staging.

High-Resolution MRI Checklist for Rectal Cancer Staging
MRI Modality
- Use MRI as the primary modality for staging rectal cancer.
- Avoid relying solely on CT, ERUS, or PET-CT.
Image Quality
- Use high-resolution T2-weighted Fast Spin-Echo sequences.
- Avoid low-resolution T2 scans with large field of view.
- Do not use T1-weighted scans with contrast or fat saturation.
- Avoid diffusion-weighted imaging (DWI) for staging.
MERCURY Protocol
- Slice thickness: · 3mm
- Field of view: 16cm
- Matrix: · 256×256
- In-plane resolution: 0.6mm × 0.6mm
- Voxel size: ~1.1mm³
- NSA/NEX: 4·6
- Scan duration: ~7 minutes per sequence
Scan Orientation
- Axial scans: Perpendicular to rectal wall
- Coronal scans: Parallel to anal canal
- Coverage: At least 5cm above tumour or up to L5/S1
Motion Reduction
- Use anterior and superior saturation bands.
- Apply firm abdominal compression.
- Administer antispasmodics (e.g., Buscopan) to reduce peristalsis.
- Ensure bladder is empty before scan.
Coil Positioning
- Place surface phased array coil over lower pelvis.
- For low rectal cancers, distal edge of coil should lie 10cm below symphysis pubis.
Sequence Selection
- Use only high-resolution T2 sequences.
- Avoid T1, contrast-enhanced, fat-saturated, and DWI sequences.
- Exclude non-contributory sequences to reduce scan time and improve quality

1. Ensuring High Resolution MRI to Accurately Stage Rectal Cancer A summary guide Gina Brown www.profginabrown.com

2. Which of these best reflects your practice staging rectal cancer? CT and ERUS +/- PET-CT are staging modalities of choice at my institution MRI is sometimes/frequently used for staging rectal cancer MRI is mandatory for rectal cancer staging at my institution

3. Avoid Low Resolution T2 weighted scan 3mm slice thickness but the field of view is too large! The whole pelvis is visible including hips = Poor spatial resolution It means we cannot accurately resolve: Tumour Disease within mesorectum Relationship of tumour to mesorectal fascia

4. Avoid T1 weighted scan with intravenous contrast and fat saturation The spatial and contrast resolution is poor Fat is dark Vessels are bright Tumour is not well seen Fascial structures not visible Layers of bowel wall not seen Loss of anatomic details Debemos Evitar

5. T1 sequences for rectal cancer no useful information for TN staging! Field of view too big, cannot resolve tumor well T1 tumor and vessels are not distinguished leads to overstaging T2 high resolution - can distinguish anatomy well

6. Which types of MRI scans should you look at? 1 2 3 8 Fat sat T1 with dynamic contrast Small field of view T2 FSE STIR, T2 fat sat

7. Slice 1 Slice 2 Slice 4 Slice 3 Slice 5 Slice 6 Learning from Pathology Slice 1 Slice 2 Slice 3 Slice 6 Slice 4 Slice 5 Depth of spread/mm High Resolution T2 weighted Fast Spin-Echo MRI scan Mesorectal fascia vessels Lymph nodes Distance to CRM

8. MERCURY Standardised Technique Slice thickness 3mm 16cm Field of View 4-6 NSA Min 256x256 matrix TR >3,000, TE 80-100, ETL 16 In plane resolution 0.6mm x 0.6mm Brown et al BJR 2005, MERCURY BMJ 2006, MERCURY Radiology 2007, JCO 2011, 2013

9. Sagittal T2w TSE FOV 250 RFOV 100% 24 slices 3/.0.4mm Foldover direction AP 2 rest slabs anterior & superior TSE factor 23 TE 125 TR 3961 Matrix 320/512r Scan % 100 NSA 4 Scan length 6mins

10. 1. Ensure scans are T2 weighted high resolution Field of view and matrix parameters should not exceed a pixel size of 0.6mm x 0.6mm Either 200mm x 200mm with 384 x 384 matrix Or 160mm x 160mm with a 256 x 256 matrix pixel size in mm = field of view/matrix voxel size mm 3 = pixel size x slice thickness We need a voxel size of 1.1mm 3

11. High res vs non high res The difference between a high resolution and suboptimal MRI scan. The difference in technique can make a substantial but entirely avoidable difference to staging accuracy. High res –showing Early T2 tumour Non-High res Same patient – T stage? High resolution voxel 1.1mm 3 Same patient low resolution voxel 1.7mm 3

12. 2. Ensure planes are correct Phased array Coil positioning critical High Res Axials perpendicular to rectal wall Coronal imaging parallel to anal canal Don’t forget discontinuous disease higher in the mesorectum Brown et al BJR 2005

13. Correct Scan planes Scans should be obtained perpendicular to the rectal wall , the sagittal MRI scans are used to plan the oblique axial images Coronal images should be undertaken parallel to the anal canal to visualise the distal anorectum and distal mesorectal plane Tumour nearly always spreads upwards into the mesorectum High resolution coverage should include at least 5cm above the top of the tumour and to the L5/S1 level for all tumours to ensure that discontinuous tumour spread can be visualised

14. 3. Use of Sat Bands and firm abdominal compression to limit abdominal wall motion The use of anterior and superior saturation bands reduce image degradation due to abdominal wall motion and   hyoscine butylbromide given as an i.m . injection or oral mebeverine reduces small bowel peristalsis respectively Without Sat Bands With Sat Bands

15. What is the T stage of this tumor? T1 Sm3 T2 0mm spread T2/T3a <1mm spread T3b 1-5mm spread T3c >5mm T4 – levator involved?

16. Reduction of physiological motion Good lower abdominal compression esp in thin patients Use of saturation bands / REST Slabs If phase AP Swap Phase direction R-L

17. Empty bladder Use of anti- spasmodics

18. Peristalsis – use of antispasmodics before and after i.m. buscopan

19. 4. Correct Coil Position The surface phased array coil should be placed correctly over the lower pelvis. For low rectal cancers the distal edge of the coil should lie 10cm below the symphysis pubis to ensure that the distal rectum is in the centre of the image

20. 5. Other Sequences? T1 weighted imaging, contrast enhanced imaging and fat saturated sequences do not contribute and worsen staging accuracy and should not be used for primary rectal cancer staging. Avoid using diffusion weighted imaging for rectal cancer as it does not improve staging accuracy when compared with high resolution MRI techniques and adds unnecessary scan time. The prolonged examination time caused by additional non-contributory sequences reduces the overall quality of the examination as well as prolonging patient discomfort.

21. DWI has insufficient resolution to distinguish tumour from fibrosis – no evidence for its added value if high resolution T2 scans are done b а с d

22. Fat Saturation and Contrast Enhancement Does not improve accuracy Tumour and normal anatomy both enhance and are not distinguished

23. Low rectal tumours Series 1: perpendicular to the anal canal, assesses centre complex in the axial plane Series 2 perpendicular to the rectal wall. Series 3 parallel to the long axis of the anal canal Series 4: parallel to the sacral promontory, enables assessment of mesorectal nodes tumour deposits and vascular invasion 1 4 2 3

24. Mid rectal tumours Series 1: perpendicular to the rectal wall Series 2 : perpendicular to the sacral promontory above the tumour – ensure at least 5cm above the top of the tumour is covered or coverage is up to L5/S1 (whichever is higher) 1 2

25. Technique Summary of Essentials Scan duration = quality 7mins average length of each sequence 4-6 NSA/NEX and T2- FSE / TSE /FRFSE 0.6mm x 0.6mm x 3mm = 1.1mm3 voxel Adequate coverage – 5cm above top of tumour Perpendicular to the rectal wall Low rectal cancer – parallel to anal canal Ensure discontinuous deposits are covered on high res Buscopan - i.m. improves quality Saturation Bands Firm coil placement with secure abdominal compression www.profginabrown.com