Optimization of ct scan protocol in acute abdomen 2003 revised aa
1. Optimization Of CT Scan Protocol In
Acute Abdomen
(
Dr Hisham Al Khatib
Consultant Radiologist
Prince Sultan Military Medical City
2. Objectives
• Learn definition & causes of acute abdomen.
• Learn CT scan protocol for acute abdomen
• Learn typical CT scan findings in common
conditions of AA
3. Acute Abdomen
Any clinical condition characterized by severe
abdominal pain that develops over period of
hours ,+l- abdominal tenderness or rigidity
urgent therapeutic decision
4. Acute Abdomen
• Often difficult to diagnose
• Clinical presentation, physical examination can
be very nonspecific
• Laboratory exams: non‐diagnostic or not
specific
6. Acute Abdomen
Diagnostic work up
Abdominal plain film Ultrasound
CT MRI
Which is the best choice?
7. Acute Abdomen
Diagnostic work up
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
11. 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,
12. How do you design a CT protocol
• components
– Scanning parameters
– What do to the patient
• eg contrast when , how , and how we doing
– Dose information
– filming
– network instruction
– billing code
13. Scanning parameters
• CT machine
• kVp
• mAs
• Slice collimation
• Slice thickness
• Interscan spacing
• Reconstruction algorithm for different tissues
14. 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 ( isotropic voxel)
15.
16. kVp
• Between 80-140
• Higher kVp: in routine CT abdomen
• Lower KVp: CTA, perfusion studies
• Manual versus automatic KVp selection:
– Care kV, Siemens machine
17. Tube current
• mAs selected should result in diagnostic
quality images
• Most body CT and even head CT: Use AEC
18. Tube current
• For all patients less than 20 years old, set the
minimum mA to 80 for all studies.
19. Collimation
• Narrow collimation and small reconstruction
intervals can help detect calculi in the biliary
system and genitourinary tract.
• Affects
– Total scan time
– Noise / Low contrast resolution
– Thinnest available recons
• Some configurations (esp. narrow collimations)
are less dose efficient (vendor-specific)
20. • 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
21. 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.
22. 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.
23. CT Image suitable for diagnostic
purpose :
– Low noise
– High contrast resolution
– Sharpness of image
– Absence of artifacts
24. Pediatric protocols
• should be adjusted regarding exposure
parameters
• Protocol optimization reducing radiation dose:
– mAs according to patient size and weight
– Implementation of automatic control sysyem
27. oral contrast
Types
• Water neutral: negative contrast used in
most cases
• Water soluble positive contrast
– Ominipaque 350
– Gastrografin agent (2% – 4%)
– Diluted barium suspension (1% – 2%) e.g., EZCAT
28. 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
29. 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
30. 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
31. Rectal contrast
• may be used in
– appendicitis
– diverticulitis
– leak or perforation
– colonography
– penetrating injury
32. 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
33. IV Contrast
• is recommended in most cases.
• Exceptions:
• include evaluation of suspected ureteral colic,
retroperitoneal hge or
• contraindication to contrast
34. 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
• Consider using a lower osmolar agent (Visipaque) in
patients with diabetes and renal insufficiency
•
35. Diabetics taking Metformin (glucophage)
• should be stopped for 2 days after CT &
creatinine checked prior to restarting Metformin
• If creatinine is normal (< 1.5), I.V. contrast may be
given;
• If creatinine > 1.5,do not administer I.V. contrast.
• Contact clinician &reschedule patient.
• Contact referring clinician to obtain lab values.
36. Premedication
Allergy pateints
• Oral: 50 mg p.o. of prednisone 13 h., 7 h. and 1 h.
prior to procedure and
• 50 mg p.o. of Benadryl 1 h. prior to procedure.
These patients should be accompanied to the
hospital; they should not drive after taking
Benadryl
• IV: 200mg hydrocortisone 6h and 2h prior to
procedure and 50 mg p o of Benadryl 1h prior to
procedure
37. 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
38.
39. 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.
40. IV access
CTA's :
• During power injections, the site must be closely
monitored during the first 15 to 20 seconds to
prevent extravasation
• Some PICC 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.
41. 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 or go to E.R. if
swelling/pin worsen
• Skin sloughing is rare, can require a referral to
plastic surgeon
42. 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.
43. 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
44. 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. Administer N acetylcysteine (Mucomyst)
– 3. Use a reduced dosage.
– 4. If the patient is on dialysis with no renal function,
they can be given contrast, preferably prior to dialysis.
– 5. If the patient is on dialysis with borderline function,
the nephrologist should be consulted prior to contrast
use.
45. 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
46. GeneralHints
• 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
47. GeneralHints
• 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
50. 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
51. Inflamed appendix Normal appendix
The appendix (arrows) is fluid-
filled and distended with
periappendiceal fat-stranding.
52. 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).
54. 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
55. 51-year-old woman
obstructing calculus in the midureter
right hydronephrosis
56. 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
57. Acute Pancreatitis
• RS=0.5, narrow collimation , thin
reconstructions, apply radiation protection
facilities in the machine ( ASIR , Care dose )
• scan entire pancreas in single breath hold for
all phases.
58. 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.
59. 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
60. 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.
62. Small Bowel Obstruction
• common cause of acute abdomen
• adhesions most common (64%–79%)
• hernia (15%–25%),
• tumor (10%–15%)
63. 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
64. Small Bowel Obstruction
low-grade obstruction:
• oral contrast
• improves accuracy in detection of
inflammation & abscesses
• optimize identification of a transition zone
66. 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
67. 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
68. Gastrointestinal Perforation
• If possible, oral & IV contrast should be used
• to help localize perforation & characterize
complications
• Such as peritonitis and abscess formation.
70. • 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
71. 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 noncon
scan may be diagnostic.
74. AORTIC DISSECTION
• Scan method:
– RS=0.5, narrow collimation , thin reconstructions,
apply radiation protection facilities in the machine
( ASIR , Care dose )
– Non contrast – show intramural hematoma not
well seen with contrast.
• Top of arch to iliac crests
75. 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
77. LOWER EXTREMITY RUN-OFF
• Contrast:
• IV contrast at 4-5mL/sec for 125 mL (consider
increasing to 150 for very tall patients)
78. LOWER EXTREMITY RUN-OFF
• Scanning method
– RS=0.5, narrow collimation , thin reconstructions,
apply radiation protection facilities in the machine
( ASIR , Care dose )
– Noncontrast: From diaphragmatic hiatus through
toes
– Arterial:
79. LOWER EXTREMITY RUN-OFF
• SMART PREP over knees – 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
80. Sharing protocol files
• Once protocols are made
– Educating the CT technologists
– Saving CT protocols on individual scanners
– Ensuring protocols for head go to head section
only
– Trial run in few cases – Review of images‐
81. 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
82. Conclusions
• Optimize the patient preparation
• Choose the best scanning protocol for
individual patient
• Optimize the dose profile for the patient
• proper technique and protocol is essential for
optimizing the CT examination and maximizing
diagnostic accuracy
