CT Scan Technique of Abdomen

INDICATIONS:

1. To evaluate cystic disease of abdominal organs.
2. To evaluate solid tumors of abdominal organs such as Hepatocellular Carcinoma, Adenocarcinoma, Haemangioma etc.
3. To demonstrate inflammatory changes of abdominal organs such as cirrhosis, abscess, cholecystitis, cholelithiasis, pancreatitis, ascitis, peritoneal metastasis, pyelonephritis etc.
4. In case of trauma of abdominal organs such as renal trauma, splenic trauma, peritoneal trauma etc.
5. Planning of radiation therapy for cancer of abdominal organs.
6. Guiding the passage of needle used to obtain a tissue sample.
7. Initial staging of GIT neoplasms.
8. Detecting and staging post operative recurrence of tumor.
9. Detection and characterization of bowel obstruction, perforation and trauma.

PATIENT PREPARATION:

1. Patient is asked to wear comfortable, loose fitting clothing for CT scan.
2. Come with empty stomach for about 6 hours before scanning for CECT. No need for NCCT.
3. Anything that might interface with imaging abdomen such as belts, keys should be removed.
4. The patient must be instructed to void and empty the urinary bladder 1 hour before the start of the exam.
5. Patient is asked to arrive 1 hour before the scanning and should be given oral contrast first dose 45 minutes before study, second dose 30 minutes prior to the study and third dose just before scanning.
6. Explain the patient about the CT machine and the breathing commands as the patient must be familiar oneself with the procedure and be able to co-operate during the examination.
7. Consent should be taken before the injection of contrast.

PATIENT POSITIONING:

1. Patient is asked to lie down on the couch in supine position.
2. Arms are usually positioned above the head to eliminate artifact and instruct patient not to move during scanning.
3. Patient is positioned into the gantry with the help of laser light accurately.
4. Height and position of table is fixed and cleared to make table position zero.

TECHNIQUE:
1. Patient data is entered into the register in the computer.
2. Scanogram of the abdomen is taken with the following parameters:

• Scan collimation 5 mm
• Scan length 500 mm
• Filter 2
• Mode PA
• Tube orientation Inward
• KV/mA 120 KV/100mA
• Matrix 512

3. Routine abdomen CT is performed in axial axis.
4. Slices are started from the top level of dome of diaphragm to the iliac crest in case of upper abdomen and for pelvic cavity from iliac crest to symphysis pubis.
5. Slice thickness varies but routine study slices are of 8-10 mm thick.
6. Field of view is adjusted according to the size of the body.
7. Normal scan is started with following protocol:

• Thickness 10 mm
• mA 200
• FOV 350 mm
• Index 10
• Scan time 1 sec
• KV 120 
• Matrix 512
• Filter 3

8. After finishing the plain normal scan CM is injected through the median antecubital vein according to the dose required for patient (80-100ml).
9. In general CM is injected for indication which includes determining the vascular characterization of mass, differentiation of a vascular anomaly or abnormality from a neoplasm and maximizing lesion detectability.
10. After scan is finished, scan is stopped and couch is taken out from the gantry and gantry is parked at its original position.
12. All the iamges with topogram is printed with proper WW (240) and WC (40) on 14"x17" film in 5x6 format. Then film is developed or may receive as dry film by dry silver image processor.

CT SCAN OF LIVER:

1. When liver is the organ of interest, 10 mm slice of entire organ is done including upper abdomen and a part of pelvis.
2. The best time to scan the liver is when difference between CM concerned within the normal liver tissue and the lesion is greatest. This difference vary for different lesions.
3. The hypo vascular lesions are best displayed during the relatively dense arterial and venous enhancement.
4. For hyper vascular lesions, it is desirable to perform dense arterial and venous enhancement. This lesion are also dense arterial enhanced, they become hyper dense compared with the surrounding normal tissue.
5. To display intra-hepatic tumor- Delayed scanning technique is performed. Scanning is often performed when CM has cleared from normal liver parenchyma but not from abnormal tumor tissue.

CT SCAN OF PANCREAS:

1. With the patient in supine position, the IV CM is given as a continous drip infusion or as a multiple bolus injections for scanning.
2. Then, the patient is placed in right decubitus position and given 100-200 ml of oral contrast and rescanned. This technique is valuable as it eliminates any false positive possibilities, such as:

• Mass in the pancreatic head vs oral contrast in gastric antrum or duodenum.
• Mass in the region of body and tail of pancreas vs oral contrast filled jejunal loops.

3. With the bolus injection method combined with dynamic scan, a more complete assessment of the vascular flow characterization is possible which shows arterial capillary and venous phase enhancement on each scan used for vascular tumor such islet cell tumor.