LIVER AND SPLEEN
| Preparatory steps: | |||
| - | Indications: suspected or known focal or diffuse disease of the liver, biliary tree, gallbladder, spleen or adjacent structures | ||
| - | Advisable preliminary investigations: ultrasonography; MRI may be an alternative examination without exposure to ionising radiation | ||
| - | Patient preparation: information about the procedure; exclude high density contrast media form previous investigations; oral contrast media for bowel and stomach demarcation; 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 | Entire liver | ||
| 1.1.2 | Entire spleen | ||
| 1.1.3 | Vessels after intravenous contrast media | ||
| 1.2 | Critical reproduction | ||
| 1.2.1 | Visually sharp reproduction of the liver parenchyma and intrahepatic portal veins | ||
| 1.2.2 | Visually sharp reproduction of the liver veins | ||
| 1.2.3 | Visually sharp reproduction of the structures of the liver hilus | ||
| 1.2.4 | Visually sharp reproduction of the common hepatic duct | ||
| 1.2.5 | Reproduction of the ductus choledochus (common bile duct) in the pancreatic parenchyma | ||
| 1.2.6 | Reproduction of the gallbladder wall | ||
| 1.2.7 | Visually sharp reproduction of the splenic parenchyma | ||
| 1.2.8 | Visually sharp reproduction of the splenic artery | ||
| 1.2.9 | Visually sharp reproduction of the extrahepatic portal vein system including v. lienalis and v. mesenterica sup. | ||
| 1.2.10 | Visually sharp reproduction of the aorta and inferior vena cava | ||
| 1.2.11 | Visually sharp reproduction of the origin of the coeliac trunk | ||
| 1.2.12 | Visually sharp reproduction of the mesenteric artery | ||
| 2. | CRITERIA FOR RADIATION DOSE TO THE PATIENT | ||
| 2.1 | CTDIW | : | 35 mGy (pilot study (17)) |
| 2.1 | DLP | : | 900 mGy cm (pilot study) |
| 3. | EXAMPLES OF GOOD IMAGING TECHNIQUE | ||
| 3.1 | Patient position | : | supine with arms at chest or head level |
| 3.2 | Volume of investigation | : | from above diaphragm to 1 cm below the caudal end of the liver and spleen |
| 3.3 | Nominal slice thickness | : | 7-10 mm; 4-5 mm if small lesions are suspected, serial or preferably helical |
| 3.4 | Inter-slice distance/pitch | : | contiguous or a pitch = 1.0; <10 mm or a pitch up to 1.2 - 2.0 in screening investigations |
| 3.5 | FOV | : | adjusted to the largest diameter of the abdomen within the volume under investigation |
| 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 | : | soft tissue/standard |
| 3.10 | Window width | : | 150-300 HU |
| 3.11 | Window level | : | 40-80 HU (enhanced examination) 0-30 HU (unenhanced examination) |
| 4. | CLINICAL CONDITIONS WITH IMPACT ON GOOD IMAGING PERFORMANCE | ||
| 4.1 | Motion | - | movement artefact deteriorates the image quality. This is prevented by standard breath-hold technique; alternatively if this is not possible scan during quiet respiration |
| - | cardiac motion may cause artefacts in left liver lobe | ||
| 4.2 | Intravenous contrast media | - | useful to delineate organ tissue and vessels and detect focal lesions in solid organs |
| - | multiphased section examination may be indicated | ||
| 4.3 | Problems and pitfalls | - | inconsistent breath holding between slices may obscure subtle pathology in serial CT |
| - | differentiation of small hepatic or splenic cysts from tumours can be difficult | ||
| - | inhomogeneous attenuation during initial contrast enhancement may mimic focal hepatic or splenic disease | ||
| - | non-calcified bile stones may not be identifiable | ||
| 4.4 | Modification to technique | - | in case of suspected haemangioma, serial CT of the pathology several minutes after injection of contrast media |
| - | additional thinner slices may be obtained to delineate subtle alterations | ||