Transcript Mid Term Revision Directed Study 1

Mid Term Revision Directed
Study 1
Dr Mohamed El Safwany, MD.
Advanced tumor detection
and characterization
Taking vascularity and perfusion type into account,
lesions such as hepatic adenomas, focal nodular
hyperplasia and less-differentiated hepatocellular
carcinomas, as well as endocrine metastases and
sarcomas, will result in hyperattenuation. Metastases
of other origins will show hypoattenuation with
various temporal characteristics in the early arterial
phase [6]. If a monophase and monoslice CT technique
is applied, many of the hypervascular hepatic
lesions will be completely invisible, but up to 30 %
more lesions are detected in the early arterial phase
compared with the portal venous phase
Acquisition of multiple perfusion
phases
• slice thickness 3.2 mm
• reconstruction interval 1.6
• pitch 1.2
• gantry rotation 0.5 s
• field of view 350–450 mm
• 150–200 mAs
As the scanning process is usually initiated simultaneously
with the beginning of an intravenous
contrast injection of 120 ml of low osmolar, nonionic
contrast agent at an injection rate of 5 ml/s,
no bolus tracking techniques are necessary. Contrast
agents with higher iodine concentrations
(370–400 mg I/ml) may be advantageous in CT
hepatic imaging, especially in the visual evaluation
of the arterial phase detectability of hepatocellular
carcinomas
The first spiral scan is acquired simultaneously
with the beginning of the contrast injection, and
therefore without any hepatic contrast
enhancement
The second spiral liver scan, approximately
10 seconds after contrast initiation, usually
shows
moderate contrast enhancement of the
abdominal
aorta and the hepatic artery, without admixture
of enhanced portal venous blood
The late arterial phase, acquired approximately
20 seconds after contrast initiation, leads to a
clear
depiction of the hepatic artery and its branches,
due to a distinctive contrast enhancement
CT Angiogram
• Quickly becoming the test of choice for initial evaluation of a
suspected PE.
• CT unlikely to miss any lesion.
• CT has better sensitivity, specificity and can be used directly to
screen for PE.
• CT can be used to follow up “non diagnostic V/Q scans.
Pulmonary angiogram
• Gold Standard.
• Positive angiogram provides 100% certainty
that an obstruction exists in the pulmonary
artery.
• Negative angiogram provides > 90% certainty
in the exclusion of PE.
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,
Scanning parameters
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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)
• 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.
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
CT -HCC
pre contrast
Arterial enhancement
(central and early)
Washout on portal venous
indicates fast flow
HCC Summary
• US - usually heterogeneous Usually HepB +ve with raised
alpha FP
• CT – C- low density
C+A – central early contrast (high flow rate)
C+PV – washout cf with liver
– may have a capsule
• MR – intracellular fat on T1 out of phase
- similar perfusion characteristics to CT
CT COLONOGRAPHY
Dissection
Strip, anus
to caecum
Endoluminal
(for fun only)
Orientation
Overview
800/40 window
Axial to loops
Advantages / disadvantages
• Sensitivity and specificity is of the order of 90 % for 10
mm polyps.
• Easy, quick and well tolerated.
• Beats barium enema hands down.
• Safer than optical colonoscopy
• Approx. half the price of optical colonoscopy
• No intervention possible as in optical Cy
• At present for “Ba enema” indications, but is likely to
be used for screening in future.
• Radiology manpower training required.
• Radiation dose equivalent to Ba Enema
Incomplete air column -Excess fluid
Supine
Prone
Diverticular disease
CT ENTEROCLYSIS
Jejunum often thick-walled
Can evaluate bowel wall due to
negative contrast in lumen and
IV contrast in wall.
Evaluates stomach well also
Plus standard CT
Reserved for older patients due
to radiation dose
Renal Vasculature Evaluation Using A
Multidetector CT
Scanner
The technique consists of image acquisition, image
processing and finally image display. As regards
the image acquisition the following was our
protocol: 100cc of iodinated contrast was injected
at 2.5 ml/sec, using automated techniques e.g.:
care bolus (for beginning of acquisition). Images
that were obtained were of 1.25 mm slice thickness
with 1mm slice collimation.
Scanning is done from the twelfth dorsal or the first lumbar
vertebral level to the level of the pubic symphysis. After the
arterialphase, a venous phase is followed using same image
acquisition parameters (60 cc after contrast). Further
which a delayed acquisition (12/15 min after contrast
injection) is done with 5mm slice and 5mm collimation to
image the pelvicalyceal system, ureter and bladder. No
oral contrast is used. Acquired images were axially
reconstructed with overlapping slices and transferred to
an imaging workstation
MIP reconstruction is the
technique of choice for image
presentation because it is able
to produce angiography
like images
REQUIREMENTS FOR CTA
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PATIENT PREPARATION
ACQUSITION PARAMETERS
CONTRAST MEDIUM ADMINISTRATION
POSTPROCESSING TECHNIQUES
PARAMETERS
• USUALLY ROUTINE CT PRECEDES A CTA EXAM.
THE ROUTINE EXAM IS USED AS A REFERENCE
SCAN HELPING TO DETERMING THE
SCANNING RANGE IN CTA.
SLICE THICKNESS
• SLICE
THICKNESS
• SPATIAL RESOLUTION
SLICE THICKNESS
• CEREBRAL CTA
• 1MM (LOWER mA)
• ABDOMINAL CTA
• 3MM
• THORACIC CTA
• 3MM
SPIRAL PITCH
• PITCH
• SPATIAL RESOLUTION
TWO TECHNIQUES TO REDUCE MOTION
ARTIFACTS IN CARDIAC CT
• PROSPECTIVE TRIGGERING
• RETROSPECTIVE GATING
3-D VISUALIZATION TOOLS IN CTA
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MPR
MIP
SSD
VR
CINE
Good Luck