Optimization Of CT Scan Protocol In Acute Abdomen

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Optimization Of CT Scan Protocol In Acute
Abdomen

• Dr Mohamed El Safwany, MD.

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Objectives

• Learn definition causes of acute abdomen.
• Learn CT scan protocol for acute abdomen
• Learn typical CT scan findings in common
  conditions of AA

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Acute Abdomen

• Any clinical condition characterized by severe
• abdominal pain that develops over period of
• hours ,l- abdominal tenderness or rigidity
• Acute Abdomen
• urgent therapeutic decision

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Acute Abdomen

• Acute Abdomen
• Often difficult to diagnose
• Clinical presentation, physical examination can
  be very nonspecific
• Laboratory exams non-diagnostic or not specific

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Acute Abdomen

• Imaging is the cornerstone of evaluation

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Acute Abdomen

• Diagnostic work up
• Acute Abdomen
• Abdominal plain film Ultrasound
• CT MRI
• Which is the best choice?

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Acute Abdomen
Diagnostic work up Acute Abdomen Which is the
first line imaging modality used for the upper
right quadrant and pelvic pain? 1) CT 2) US 3)
MRI 4) Abdominal plain film
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• Diagnostic work up
• Acute Abdomen
• US
• CT

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Causes of Acute Abdomen

• 28 Acute appendicitis
• 10 Acute cholecystitis
• 4 Bowel obstruction
• 4 Gynecologic diseases
• 3 Acute pancreatitis
• 3 Renal colic
• 2 Perforated duodenal ulcer
• 2 Acute diverticulitis
• 33 Unknown cause

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Optimization Of CT Scan Protocol In Acute Abdomen
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Scan Protocols

• core of every CT examination.
• protocols should be appropriate for the clinical
  indication
• should include all aspects of the exam such
• positioning,
• nursing instructions,
• scan parameters( including radiation dose)
• reconstruction/reformatting instructions,

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How do you design a CT protocol

• components
• Scanning parameters
• contrast when , how
• Dose information
• filming
• network instruction

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Scanning parameters

• CT machine
• kVp
• mAs
• Slice collimation
• Slice thickness
• Interscan spacing
• Reconstruction algorithm for different tissues

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Scanning parameters

• multislice CT is better than single slice
• MSCT
• High quality
• Wider range of examination
• Thinner slices
• Shorter scan time
• Multiphases protocol
• Better reconstruction

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kVp

• Between 80-140
• Higher kVp in routine CT abdomen
• Lower KVp CTA, perfusion studies
• Manual versus automatic KVp selection Care kV,
  Siemens machine

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Tube current

• mAs selected should result in diagnostic quality
  images
• Most body CT and even head CT Use AEC

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Tube current

• For all patients less than 20 years old, set the
  minimum mA to 80 for all studies

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Collimation

• Narrow collimation and small reconstruction
  intervals can help detect calculi in the biliary
  system and genitourinary tract.

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• Slice thickness Acquire thins, reconstruct
  thick Less noise
• Scan coverage scan length
• Rotation speed Keep fastestfor most regions to
  allow breath hold tech and more coverage

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Increment

• is the distance between the reconstructed images
  in the Z direction.
• When the chosen increment is smaller than the
  slice thickness, the images are created with an
  overlap.

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Increment

• is useful to reduce partial volume effect, giving
  you better detail of the anatomy and high quality
  2D and 3D post-processing .
• can be freely adapted from 0.1 - 10 mm.

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CT Image suitable for diagnostic purpose

• Low noise
• High contrast resolution
• Sharpness of image
• Absence of artifacts

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Pediatric protocols

• should be adjusted regarding exposure parameters
• Protocol optimization reducing radiation dose
• mAs according to patient size and weight
• Implementation of automatic control system

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contrast

• Oral
• I.V
• Rectal
• Urinary bladder .....etc

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Oral Contrast

• Type of contrast
• Volume of contrast
• Timing of contrast

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oral contrast Types

• Water neutral negative contrast used in most
  cases
• Water soluble positive contrast
• Ominipaque 350
• Gastrografin agent (2 4)

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oral contrast Volume

• Upper abdomen
• Minimum 700-1000 ml of contrast
• divided into 3 cups (approximately 250 300 ml)
• 1st cup,30 minutes before exam
• 2nd cup,15 minutes before exam
• 3rd cup , 5 minutes before exam

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oral contrast Volume

• Abdomen-Pelvis
• Minimum 1000 ml
• divided into 4 cups
• 1st cup ,1 hour before exam
• 2nd 4th cups every 15 minutes
• Start exam 5 minutes after the 4th cup

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oral contrast

• Use in
• Suspected appendicitis
• Fistula
• Leakage of contrast anatomosis gastric bypass
• Perforation
• Not used in
• High intestinal obstruction
• Ureteric colic
• Intestinal bleeding
• Vascular cuases

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Rectal contrast

• may be used in
• appendicitis
• diverticulitis
• leak or perforation
• colonography
• penetrating injury

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IV Contrast

• opacifies abdominal vasculature and
• provides useful information regarding enhancement
  of the parenchymal organs and intestine
• 100-120 mL of iodinated contrast material
  injected
• rate of 3-5 mL per second is adequate

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IV Contrast

• is recommended in most cases.
• Exceptions
• include evaluation of suspected ureteral colic,
  retroperitoneal hge
• contraindication to contrast

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IV contrast

• Normal creatinine level , should be within a
  month
• High creatinine level , to be discuss with
  ordering physician
• Look for
• renal disease , hypertension, diabetes
  ,malignancy

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Premedication Allergy pateints

• Oral 50 mg of prednisone 13 h., 7 h. and 1 h.
  prior to procedure and
• IV 200mg hydrocortisone 6h and 2h prior to
  procedure and 50 mg p o of Benadryl 1h prior to
  procedure

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Technical aspect of acute abdomen CT Imaging

• IV contrast should be given at 3-5 ml/sec
• total of 100-120 mL,
• followed by saline
• Use SMART PREP or threshold tech

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IV access

• CTA's
• high rates of injection,
• a large bore IV, 18 g or larger is required
• Do not use hand/forearm veins
• Antecubital only.

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IV access

• CTA's
• During power injections, the site must be closely
  monitored during the first 15 to 20 seconds to
  prevent extravasation
• Some catheters are designed for use with power
  injectors,
• Check the label of any catheter for maximum flow
  rate and pressure.
• Adjust the settings on the power injector
  accordingly.

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Contrast extravasation

• most are small self limited.
• Ice pack and elevate for 20 mins.
• If swelling/pain resolved patient can be
  discharged
• Advise patient to contact MD if swelling worsen
• Skin sloughing is rare, can require a referral to
  plastic surgeon

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Contrast extravasation

• Compartment syndrome
• with large volumes in the forearm/hand.
• pain with extension of fingers.
• May lose pulses
• become cold/discolored.
• requires referral to plastic/orthopedic/hand
  surgeon.

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Renal Function/Creatinine levels

• Patients with pre-existing renal failure or
  Diabetes Mellitus should have creatinine levels
  checked when the exam is non-emergent
• In general, a creatinine of 1.8 or less is
  acceptable for non-ionic contrast use

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Renal Function/Creatinine levels

• For Creatinine levels above 1.8 there are several
  options
• 1. Withhold contrast if indication for contrast
  use is equivocal
• 2. Use a reduced dosage.
• 3. If the patient is on dialysis with no renal
  function, they can be given contrast, preferably
  prior to dialysis.
• 4. If the patient is on dialysis with borderline
  function, the nephrologist should be consulted
  prior to contrast use.

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Contrast Allergy

• Patients with prior severe/life threatening
  reactions should avoid contrast if at all
  possible
• For other prior reactions, pre-medicate with
• oral prednisone 50mg 13 hrs,7 hrs 1 hr prior to
  injection and oral benadryl 50 mg 1 hr prior

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General Hints

• Topogram AP, 512 or 768 mm.
• Patient positioning Patient lying in supine
  position, arms positioned comfortably above the
  head in the head-arm rest lower legs supported.
• Patient respiratory instructions inspiration
• Scout AP and lateral

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General Hints

• Limit scan to intended anatomic area to cut dose
  by 10
• Abdomen
• Just above diaphragm Inferior pubic symphysis
• Chest
• Routine Apex to adrenals
• PE or benign clinical reasons Apex to lung bases

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Common causes of acute abdomenPractical aspect
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Appendicitis

• most common causes of acute abdominal pain
• Most 1000 cc oral contrast before about 1 hour
  before
• Others give oral rectal
• Scanning after 70 second from IV injection ,
  might need delayed scan

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Acute Pyelonephritis

• Fever, chills, and flank tenderness.
• referred for CT when symptoms are poorly
  localized or suspected complications .
• nephrographic phase (7090 seconds after
  injection) or
• excretory phase (5 minutes after injection).

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Ureteral Stones

• continuous breath-hold acquisition from kidneys
  to bladder base.
• Narrow (3-mm) collimation and small
  reconstruction intervals (also 3 mm) are
  essential for optimal detection of small calculi
• Prone scans may be needed to differentiate a
  ureterovesical junction stone from a recently
  passed stone

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Acute Pancreatitis

• Contrast
• Patient should drink water as the oral contrast,
  OPACIFICATION AND DISTENTION OF DUODENUM IS VERY
  HELPFUL
• IV contrast at 4-5mL/sec for 120 mL

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Acute Pancreatitis

• narrow collimation , thin reconstructions, apply
  radiation protection facilities in the machine
• scan entire pancreas in single breath hold for
  all phases.

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Acute Pancreatitis

• Acute Pancreatitis
• Noncontrast Liver dome to iliac crests
• Arterial phase Initiate scan at 25 sec. Use
  SMART PREP Aorta (150HU) to monitor those with
  poor cardiac output. Top to bottom of liver.
  Ideally obtain excellent pancreatic parenchymal
  arterial opacification with minimal contrast in
  portal vein.

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Acute Pancreatitis

• Portal venous phase 80 sec delay. Scan the
  entire abdomen in this acquisition (top of the
  liver to sp).
• Delayed 3 minute scan through liver and kidneys.
• Coronal and sagittal reformat of portal venous
  phase

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Diverticulitis

• rectal contrast
• is highly accurate for diagnosis
• Most use 400800 mL of 3 iodinated contrast
• IV contrast
• helpful in detection characterization of
  pericolonic inflammation
• recommended in most patients.

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Small Bowel Obstruction

• common cause of acute abdomen
• adhesions most common (6479)
• hernia (1525),
• tumor (1015)

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Small Bowel Obstruction

• high-grade small bowel obstruction
• best performed without oral contrast.
• large amounts of fluid in bowel acts as a natural
  contrast agent,
• when combined with IV contrast ,allows
  opacification of bowel wall masses

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Small Bowel Obstruction

• low-grade obstruction
• oral contrast
• improves accuracy in detection of inflammation
  abscesses
• optimize identification of a transition zone

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Ischemic Bowel

• present with symptoms ranging from relatively
  minor discomfort to acute abdominal pain, which
  makes clinical diagnosis difficult
• vascular occlusion or thrombosis, whether from
  arterial or venous disease, and hypoperfusion

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Ischemic Bowel

• rapid (4-5 mL/sec) IV contrast for optimal
  vascular opacificationi
• IV contrast is essential for depiction of the
  thickened, edematous bowel wall, which can easily
  be appreciated against the obstructed,
  fluid-filled intestine
• Arterial venous phases are essential
• Water can be used as alternative for bowel lumen

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Gastrointestinal Perforation

• If possible, oral IV contrast should be used
• to help localize perforation characterize
  complications
• Such as peritonitis and abscess formation.

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Vascular System

• Aortic Aneurysm Rupture
• Aortic Dissection
• Hemorrhage

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• rapid (4-5 mL/sec) IV bolus contrast for optimal
  vascular opacification
• Narrow collimation
• high-quality 3D images
• Oral contrast material is not administered , can
  interfere with reconstruction

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AORTIC ANEURYSM

• Study should only be performed in hemodynamically
  stable patients.
• Hemodynamically unstable patients with high
  degree of suspicion of aortic pathology should go
  directly to OR.
• If becomes unstable in CT, a quick non conreast
  scan may be diagnostic.

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AORTIC DISSECTION

• Contrast
• No oral contrast
• IV contrast at 4-5mL/sec with 125 mL

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AORTIC DISSECTION

• Scan method
• narrow collimation , thin reconstructions, apply
  radiation protection facilities in the machine.
• Non contrast show intramural hematoma not well
  seen with contrast.
• Top of arch to iliac crests

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AORTIC DISSECTION

• Arterial Use HiRes HD mode, SMART PREP over
  aortic arch with threshold 150 HU, Apices to SP
• Portal Venous 80 sec delay from dome of liver
  to SP to assess organ perfusion.
• Coronal and sagittal reformat of arterial phase
• Coronal and sagittal MIP of arterial phase

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LOWER EXTREMITY RUN-OFF

• Contrast
• IV contrast at 4-5mL/sec for 125 mL (consider
  increasing to 150 for very tall patients)

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LOWER EXTREMITY RUN-OFF

• Scanning method
• narrow collimation , thin reconstructions, apply
  radiation protection facilities in the machine
• Non contrast From diaphragmatic hiatus through
  toes
• Arterial

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LOWER EXTREMITY RUN-OFF

• SMART PREP trigger scan at first blush of
  contrast. Do not use ROI!
• From diaphragmatic hiatus through toes
• Coronal and sagittal reformat of arterial phase
• Coronal MIP of arterial phase

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Sharing protocol files

• Having hard copy protocol books by body region in
  all scanner suites
• Scan length
• Scan phases or passes
• Contrast injection details
• Shared drive access to protocols with in the
  intranet from any internal personal computer
• Electronic copies of protocols with version date
  and protocol types

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Text Book

• David Suttons Radiology
• Clarks Radiographic positioning and techniques

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Assignment

• Two students will be selected for assignment.

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Question

• Define Technical aspect of acute abdomen CT
  Imaging?

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• Thank You

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