4. 1.what is the definition of CT scan?
COMPUTED TOMOGRAPHY DEFINED:
Computed tomography uses a computer to process information
collected from the passage of x-ray beams through an area of
anatomy. The images created are cross-sectional.
difference between radiography and tomography:
A. Radiography :
_The use of X-rays to view a non-uniformly composed
material such as the human body.
B. Tomography :
_Imaging by sections or sectioning.
5. 2. what are the main advantage of CT
over conventional radiography?
1. Ability to differentiate small differences in density of
anatomic structures and abnormalities.
2. Superior quality of the images.
3. Better detail compared with ultrasonography.
4. Relatively quick compared with MRI scanning.
5. Most systems can be scanned (brain to leg).
6. Benefits of CT include more
effective medical management by:
1. determining when surgeries are necessary
2. reducing the need for exploratory surgeries
3. improving cancer diagnosis and treatment
4. reducing the length of hospitalizations
5. guiding treatment of common conditions such as
injury, cardiac disease and stroke
6. improving patient placement into appropriate areas
of care, such as intensive care units
7. 3. what are the instrument we
use in CT scan?
There are essentially two types of CT scans:
A. Conventional CT scan - the scan is taken slice by slice
and after each slice the scan stops and moves down to the
next slice - e.g. from the top of the abdomen down to the
pelvis. This requires patients to hold their breath to avoid
movement artefact.
B. Spiral/helical CT scan - this is a continuous scan which
is taken in a spiral fashion. It is a much quicker process and
the scanned images are contiguous.
8. 4. what are the anatomy of liver
in the CT scan?
The anatomy of the liver can be described using two
different aspects: morphological anatomy and
functional anatomy. The traditional morphological
anatomy is based on the external appearance of the
liver and does not show the internal features of
vessels and biliary ducts branching, which are of
obvious importance in hepatic surgery.
13. 5. what are anatomic positions of
view liver in the CT scan?
Axial view - Coronal view - Sagittal view
14. Indication of liver study in CT
A- Diffuse liver diseases:
1- steatosis (Fatty Liver): its the abnormal accumulation of lipids,
particularly triglycerides within hepatocytes due to: alcohol abuse,
diabetes mellitus, and obesity.
2- cirrhosis: its chronic liver disease processes which cause
hepatocellular necrosis and often due to: alcohol: 60-70%
viral hepatitis: 10%
3- hepatitis : is an inflammation of the liver.
4- Sarcoidosis: is a systemic inflammatory disease of unknown
origin characterized by the formation of non-caseating granulomas.
5-portalvenous thrombus.
15. B- Focal liver lesion:
1- benign tumors like:
A- cysts (simple and polycystic)
B- Hemangioma: is a noncancerous (benign) mass that
occurs in the liver.
C- focal nodular hyperplasia. is a benign tumor of the
liver (hepatic tumor), which is the second most prevalent
tumor of the liver
D- hepatocellular adenoma: is an uncommon benign
liver tumour that is hormone induced. The tumours are
usually solitary and have a predilection to haemorrhage
16. 2- Malignant tumors:
A- hepatocellular carcinoma: it’s a cancer that
bring in liver.
B- cholangiocarcinoma: are malignancies of the
biliary duct system that may originate in the liver
and extrahepatic bile ducts, which terminate at the
ampulla of Vater
C- metastasis: is a cancerous tumor that has spread
to the liver from another place in the body. It is also
called secondary liver cancer
17. Contraindication
First: Related to contrast agent:
A- oral contrast: gastrografin or barium sulfate
Hypersensitivity: history of asthma, premedication with
antihistamines
Thyroid Dysfunction: known or suspected
hyperthyroidism or goitre, as iodinated contrast media may
interfere with thyroid function.
Very Poor State of Health: careful consideration in
patientswith a very poor general state of health.
18. Gastrointestinal: In case of prolonged retention of
Gastrografin in the gastrointestinal tract
(e.g.obstruction, stasis), tissue damage, bleeding,
bowel necrosis and intestinal perforation may occur.
Hydration: Adequate hydration and electrolyte
balance should be established and maintained in the
patients, since the hyperosmolarity of Gastrografin
may cause dehydration and electrolyte imbalance.
19. Second related to I.V. Contras contraindication:
There are two main contraindications for the administration of iodinated
IV contrast: contrast induced nephropathy and allergy to iodinated
contrast. Current policy suggests a creatinine of less than or equal to 1.5
mg/dl and no evidence of acute kidney injury for IV contrast
administration.
Hepatic failure.
Death brain.
Any allergic reaction.
Hemorrhage.
Vascular rupture.
20. Preparation the patient for liver scan
The patient fasting for few hours before the scan.
All metallic objects should be removed from the
area to be studied, including such items as
earrings, bobby pins and necklaces.
The patient may want to wear loose, comfortable
clothing because heshe will be required to lie
down on the table.
The patient should be instructed to empty the
bladder before the is done, because use of iv
contrast may causes the bladder to fill rapidly ,and
the scan should not be interrupted for a bathroom
break.
21. Contrast media
- Contrast material used in the liver is Iodine-based contrast
materials ,injected into a vein (intravenously) used to enhance x-ray
and CT images.
- The injection should therefore ideally have a rapid flow of2-6 ml/sec
for achieving sufficient density enhancement.
- Avenflon canula with a diameter of at least (20G)for children, or
preferably (18G-17G)for adults, is used.
22. Performing the procedure
The technologist begins by positioning on the CT examination table, scouts AP
and lateral head or feet first. Arms flexed under the head. Straps and pillows may
be used to help you maintain the correct position and to help you remain still
during the exam.
23. The technique
You may be asked to take inspiration during the scanning. Any
motion, or body movements, can lead to artifacts on the images.
Abdomen is performed with 5 mm slice thickness. Pre and post
contras medium.
Start post C.M after 10 sec
Start location: at the level of xiphisternum
End location: Just at the level of iliac crest
Liver study extend from above the xiphoid, and extend quite far
caudally to the reference point at umbilical region.
The tri-phases important from up to down arteries, from down to up
portal vein
And from up to down veins
25. cont
Next, the table will move quickly through the
scanner to determine the correct starting position for
the scans.
For spiral scanning volume acquisition 10mm slice
thickness, and 10 mm table incremented but with 5
mm reconstruction index to give over-lapping
section.
The CT examination is usually completed within a
few minutes.
33. Metastases
Multiple hypoattenuating lesions of varying sizes are
seen in both the left and right lobes of the liver, some
with indistinct margins. The patient had colorectal
carcinoma.
34. Conclusion
For treatment planning we use
Ultrasound first before other modality
because:
1- US more safer
2- low cost.
3- less preparation.
Benift for CT:
1- Has Tri-phase technique that can
localize the hepatic paranchyma and
vascular supply.
2- has more sections than US.
3- enhance the supply for tumor.
MRI:
1- better for soft tissue.
2- safe than CT
3- long time than CT.
4- worst for bone.
35. References
PROTOCOLS FOR MULTISLICE CT second edition,
Burening. A.kuettner and the flohr editors
Computed tomography for technologists, lois E. romans.
http://radiopaedia.org
Lectuer notes
http://www.epidemic.org
