ABDOMEN, GENERAL

Preparatory steps:
- Indications: inflammatory lesions, abscess, suspected or known structural alteration or space occupying lesions of the abdomen and retroperitoneum, lesions of major vessels such as aneurysms and traumatic lesions, and as a guide to biopsy
- Advisable preliminary investigations: ultrasonography and/or radiography of the abdomen. MRI may be an alternative examination with regard to the retroperitoneal space
- Patient preparation: information about the procedure; exclude high density contrast media from previous investigations; oral application of contrast media for the intestine; restraint from food, but not fluid, is recommended, if intravenous contrast media are to be given
- Scan projection radiograph: frontal from lower chest to pelvis
1. DIAGNOSTIC REQUIREMENTS
Image criteria:
1.1 Visualization of
1.1.1 Diaphragm
1.1.2 Entire liver and spleen
1.1.3 Retroperitoneal parenchymal organs (pancreas, kidneys)
1.1.4 Abdominal aorta and the proximal part of the common iliac arteries
1.1.5 Abdominal wall including all herniations
1.1.6 Vessels after intravenous contrast media
1.2 Critical reproduction
1.2.1 Visually sharp reproduction of the liver parenchyma and intrahepatic vessels
1.2.2 Visually sharp reproduction of the splenic parenchyma
1.2.3 Visually sharp reproduction of the intestine
1.2.4 Visually sharp reproduction of the perivascular retroperitoneal space
1.2.5 Visually sharp reproduction of the pancreatic contours
1.2.6 Visually sharp reproduction of the duodenum
1.2.7 Visually sharp reproduction of the kidneys and proximal ureters
1.2.8 Visually sharp reproduction of the aorta
1.2.9 Visually sharp reproduction of the aortic bifurcation and common iliac arteries
1.2.10 Reproduction of lymph nodes smaller than 15 mm in diameter
1.2.11 Reproduction of branches of the abdominal aorta
1.2.12 Visually sharp reproduction of the vena cava
1.2.13 Reproduction of tributaries to the vena cava in particular the renal veins
2. CRITERIA FOR RADIATION DOSE TO THE PATIENT
2.1 CTDIW : routine abdomen: 35 mGy
2.1 DLP : routine abdomen: 780 mGy cm
3. EXAMPLES OF GOOD IMAGING TECHNIQUE
3.1 Patient position : supine with arms at chest or head level
3.2 Volume of investigation : from dome of the liver to the aortic bifurcation
3.3 Nominal slice thickness : 7-10 mm; 4-5 mm for dedicated indications only (suspected small lesions), serial or preferably helical
3.4 Inter-slice distance/pitch : contiguous or a pitch = 1.0; in screening investigations, eg. for traumatic lesions < 10 mm or a pitch up to 1.2 - 2.0
3.5 FOV : adjusted to the largest abdominal diameter
3.6 Gantry tilt : none
3.7 X-ray tube voltage (kV) : standard
3.8 Tube current and exposure time product (mAs) : should be as low as consistent with required image quality
3.9 Reconstruction algorithm : standard or soft tissue
3.10 Window width : 150-600 HU
2000-3000 HU (bone, if required)
3.11 Window level : 30-60 HU (enhanced examination)
0-30 HU (unenhanced examination)
400-600 HU (bone, if required)
3.12 Protective Shielding : lead-purse for the male gonads if the edge of the volume of investigation is less than 10-15 cm away
4. CLINICAL CONDITIONS WITH IMPACT ON GOOD IMAGING PERFORMANCE
4.1 Motion - movement artefact deteriorates the image quality. This is prevented by a standard breath hold technique; alternatively if this is not possible scan during quiet respiration
4.2 Intravenous contrast media - useful for differentiating vessels and organ tissues from adjacent structures and to detect parenchymal lesions in solid organs
4.3 Problems and pitfalls - non-contrasted parts of the intestine may mimic tumours
  - the delineation of organs and structures may be poor in cachectic patients with reduced intra-abdominal and retroperitoneal fat
4.4 Modification to technique - helical CT which is beneficial for elimination of motion artefact can be used for demonstrating vascular pathologies (CT angiography)
  - may be combined with examination of the pelvis