Liver and gallbladder imaging
Imaging of the liver can de done with different modalities. Ultrasound is very useful for detection of various focal abnormalities such as benign and malignant changes or neoplasm. It is also useful in detection of fatty liver changes which could proceed to cirrhosis.
Although the sensitivity for detection of focal pathology is good, the specificity (what we actually see) is not always as good as could be wished. Therefore further investigations are often needed, especially with CT. Computer tomography with time-related injection of contrast medium will often characterise a lesion sufficiently.
Based upon clinical history and findings, the radiologist in co-operation with the referring doctor will tailor the best examination for different clinical settings.
Gall-bladder stones are easily detected on ultrasound, and so is dilation of the bile ducts. Diseases of the biliary system can also be visualised by NM.
Parenchymal disorders
Ultrasound can detect fatty infiltration very easily indeed, due to increased echogenicity in the parenchyma. Likewise, CT will detect similar findings because of a reduced general density (increased fat content in the liver cells). Some deposition diseases, e.g. haemosiderosis are readily detected on CT.
On the other hand hepatitis (acute or chronic) can not be detected by any imaging modality. Unspecific findings like increased liver size can be measured, but do not give any explanations as to what may be the cause.
Benign and malignant lesions of the parenchyma
Focal expansive lesions are readily detected by ultrasound, CT and MRI. The sensitivity of the different modalities varies somewhat, but for practical purposes a normal ultrasound examination may nearly always rule out significant focal pathology, provided there are no technical limitations, like significant overweight.
Simple cysts are easily detected by ultrasound, CT and MRI.
Haemangioma can often be confirmed by ultrasound or NM upon "tagging" blood cells with a radioactive marker. Some haemangioma behave differently, and in such cases dynamic CT or MRI (where several scans are taken at short intervals after injection of a contrast medium) is preferred.
Focal nodular hyperplasia and adenoma require specially tailored CT-examinations or MRI.
Metastases are mostly detected by ultrasound, but are often characterised better with CT or MRI. If surgery is planned, a preoperative mapping has to be done with either CT or MRI. Though is it important to know that a fine-needle biopsy may be mandatory to confirm the diagnosis.
Bile duct including gallbladder
Ultrasound has a very high sensitivity and specificity for detecting gallbladder stones, and also to rule out associated inflammation (cholecystitis). Ultrasound will also show dilation of the ducts which can be caused by various mechanisms. The exact cause is, however, not always demonstrated by ultrasound, so further imaging with CT or MRI in these circumstances may be necessary.
NM biliary scintigraphy shows cystic duct obstruction in acute cholangitis, will visualise post-operative bile leakage, and can diagnose biliary atresia.
GE Healthcare Glossary