Optimization Of CT Scan Protocol In
Acute Abdomen
Dr Mohamed El Safwany, MD.
Objectives
• Learn definition & causes of acute abdomen.
• Learn CT scan protocol for acute abdomen
• Learn typical CT scan findings in common
conditions of AA
Acute Abdomen
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Any clinical condition characterized by severe
abdominal pain that develops over period of
hours ,+l- abdominal tenderness or rigidity
Acute Abdomen
urgent therapeutic decision
Acute Abdomen
• Acute Abdomen
• Often difficult to diagnose
• Clinical presentation, physical examination can
be very nonspecific
• Laboratory exams: non‐diagnostic or not
specific
Acute Abdomen
• Imaging is the cornerstone of evaluation
Acute Abdomen
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Diagnostic work up
Acute Abdomen
Abdominal plain film Ultrasound
CT MRI
Which is the best choice?
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
Causes of Acute Abdomen
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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
Optimization Of CT Scan Protocol In
Acute Abdomen
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,
How do you design a CT protocol
components
•Scanning parameters
•contrast when , how
•Dose information
•filming
•network instruction
Scanning parameters
CT machine
• kVp
• mAs
• Slice collimation
• Slice thickness
• Interscan spacing
• Reconstruction algorithm for different tissues
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
kVp
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Between 80-140
Higher kVp: in routine CT abdomen
Lower KVp: CTA, perfusion studies
Manual versus automatic KVp selection Care
kV, Siemens machine
Tube current
• mAs selected should result in diagnostic
quality images
• Most body CT and even head CT: Use AEC
Tube current
• For all patients less than 20 years old, set the
minimum mA to 80 for all studies
Collimation
•Narrow collimation and small reconstruction
intervals can help detect calculi in the biliary system
and genitourinary tract.
• Slice thickness: Acquire thins, reconstruct
thick: Less noise
• Scan coverage: scan length
• Rotation speed: Keep fastest…for most regions
to allow breath hold tech and more coverage
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.
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.
CT Image suitable for diagnostic
purpose :
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Low noise
High contrast resolution
Sharpness of image
Absence of artifacts
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
contrast
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Oral
I.V
Rectal
Urinary bladder .....etc
Oral Contrast
• Type of contrast
• Volume of contrast
• Timing of contrast
oral contrast Types
• Water neutral: negative contrast used in most
cases
• Water soluble positive contrast
• Ominipaque 350
• Gastrografin agent (2% – 4%)
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
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
oral contrast
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•Use in
–Suspected appendicitis
–Fistula
–Leakage of contrast anatomosis gastric bypass
–Perforation
•Not used in
–High intestinal obstruction
–Ureteric colic
–Intestinal bleeding
–Vascular cuases
Rectal contrast
may be used in
• appendicitis
• diverticulitis
• leak or perforation
• colonography
• penetrating injury
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
IV Contrast
• is recommended in most cases.
• Exceptions:
• include evaluation of suspected ureteral colic,
retroperitoneal hge
• contraindication to contrast
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
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
Technical aspect of acute abdomen CT
Imaging
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IV contrast should be given at 3-5 ml/sec
total of 100-120 mL,
followed by saline
Use SMART PREP or threshold tech
IV access
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CTA's :
high rates of injection,
a large bore IV, 18 g or larger is required
Do not use hand/forearm veins
Antecubital only.
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.
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
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.
Renal Function/Creatinine levels
• Patients with pre-existing renal failure or
Diabetes Mellitus should have creatinine
levels checked when the exam is nonemergent
• In general, a creatinine of 1.8 or less is
acceptable for non-ionic contrast use
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.
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
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
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
Common causes of acute abdomen
Practical aspect
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
Acute Pyelonephritis
• Fever, chills, and flank tenderness.
• referred for CT when symptoms are poorly
localized or suspected complications .
• nephrographic phase (70–90 seconds after
injection) or
• excretory phase (5 minutes after injection).
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
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
Acute Pancreatitis
• narrow collimation , thin reconstructions,
apply radiation protection facilities in the
machine
• scan entire pancreas in single breath hold for
all phases.
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.
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
Diverticulitis
rectal contrast:
• is highly accurate for diagnosis
• Most use 400–800 mL of 3% iodinated
contrast
• IV contrast :
• helpful in detection & characterization of
pericolonic inflammation
• recommended in most patients.
Small Bowel Obstruction
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common cause of acute abdomen
adhesions most common (64%–79%)
hernia (15%–25%),
tumor (10%–15%)
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
Small Bowel Obstruction
low-grade obstruction:
• oral contrast
• improves accuracy in detection of
inflammation & abscesses
• optimize identification of a transition zone
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
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
Gastrointestinal Perforation
• If possible, oral & IV contrast should be used
• to help localize perforation & characterize
complications
• Such as peritonitis and abscess formation.
Vascular System
• Aortic Aneurysm Rupture
• Aortic Dissection
• Hemorrhage
• 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
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.
AORTIC DISSECTION
Contrast:
• No oral contrast
• IV contrast at 4-5mL/sec with 125 mL
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
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
LOWER EXTREMITY RUN-OFF
• Contrast:
• IV contrast at 4-5mL/sec for 125 mL (consider
increasing to 150 for very tall patients)
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:
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
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
Text Book
• David Sutton’s Radiology
• Clark’s Radiographic positioning and
techniques
Assignment
• Two students will be selected for assignment.
Question
• Define Technical aspect of acute abdomen CT
Imaging?
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Thank You