CT Colonography

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CT Colonography

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CT Colonography

• Virtual Colonoscopy
• CT -CTC
• MRI -MRC

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CA colon and rectum

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• Advanced stages
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Colonic polyp (?????????)

• ????????????? precursor of CA
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Polyp size and probability of being cancer
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Tests for CA colon and rectum

• Stool occult blood ??????????????
• Barium enema (BE) ????????????????
• Sigmoidoscopy ??????????????????????????
• Colonoscopy ?????????????????????????
• CT colonography (CTC) ????????????????????????????
  ???????

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Limitation of current tests

• Low sensitivity and specificity
• Bowel preparation
• Poor patient acceptance and compliance
• Limited availability

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Why poor acceptance?

• Lack of knowledge
• Denial
• Invasion of privacy
• Cost
• Bowel prep

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CTC vs Colonoscopy

• NOT Replacement but an Alternative
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• ??????? scope
• ????????????????? scope
• ?? scope ?????? complete
• Equally rigorous prep required ???????????????????
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CTC vs BE (barium enema)

• More sensitive and specific
• More rigorous prep
• More expensive
• Limited availability

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How to do CTC

• Three important steps
• Bowel preparation
• Patient education
• Scanning
• Adequate bowel distension
• Data processing
• Work station and CTC software
• 2D axial and 3D endoluminal views

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Bowel preparation

• Patient education
• Low to No residue diet and extra fluid intake for
  48-24 hours
• Laxative
• Lapsed time for fluid absorption

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Sample of patient instruction

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• ????????? (????????)
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Laxative

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  ???????? 2 ?????????????? ???
• ?????? 1 ????????????????????????? ????? Swiff
  45 ???? (????????) ??????????????
  ????????????????? 4..???..8..????(???????????????)
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• ?????? 2 ?????????????????????????? ????? Swiff
  ??????????? 45 ???? (????????) ???????????????????
  ?????? ?????????..4..???..8.????
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• ?????????????????????????????? ???????????????????
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Scanning procedure

• Optional Buscopan 10 mg IV about 10-15 minutes
  before scan time
• Buscopan contraindicated in glaucoma
• Put patient on CT table
• Insert rectal tube, do not blow balloon
• Insufflate colon with room air or CO2to maximum
  patient tolerance, usually around 40 puffs
• Leave rectal tube in place

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Scanning procedure (continued)

• Turn patient to supine position
• Take CT scout view, check for adequate colon
  distention
• Take scans during one breathhold
• Turn patient to prone position
• Take scout view, check for adequate colon
  distention, add more air if necessary
• Take scans during one breathhold.
• Remove rectal tube and get patient off table

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• Scanning protocol (Somatom Sensation 16)
• FOV diaphragm to symphysis/ top of flexure to
  rectum
• Position supine, prone
• Scan direction cranio-caudal
• kV 120
• mAs supine 100, prone 40
• Rotation 0.5 sec
• Collimation 0.75
• Table feed/rotation (pitch) 18.0 mm
• Reconstruction slice thickness 1.0 mm
• Reconstruction increment 0.7 mm
• Kernel B10f
• Axial supine prone optional MPR coronal
  sagittal

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Data processing

• CT workstation
• 2-D axial views (conventional CT images)
• 3-D endoluminal view generated from 2-D images
• Fly through virtual colonoscopy forward and
  turnaround backward in both positions, enabling
  detection of behind-the-fold polyp not possible
  with OC
• Analysis of findings with 2-D reference and
  comparison between positions

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Polypsupine prone
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Feces supine prone
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Colonic content supine prone
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Fluid
supine
prone
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Extracolonic findings
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Thank you