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 |