Ultrasonography (US) is often used as the modality of first choice for diagnostic imaging of gallbladder diseases. Computed tomography (CT) is also used frequently for the same purpose. These techniques are sometimes combined with MR cholangiography (1). US and CT are often used because gallbladder diseases are highly likely to involve morphological abnormalities of the gallbladder due to stones, polyps and cancer. Some gallbladder diseases involve dysfunction of the gallbladder in the absence of stones, polyps or cancer, although these diseases are less frequent than those mentioned above. The term "dysfunction" is defined as indicating motor disorders of the gallbladder without any known potential etiologic factor explaining the difficulty to differentiate purely functional alterations from subtle structural changes (2). The term "gallbladder dyskinesia" is often used to encompass gallbladder dysfunction. Gallbladder dysfunction has also been reported for patients with diseases of other organs such as liver cirrhosis, non-insulin-dependent diabetes mellitus, hypothyroidism, achalasia and spinal cord injury (3, 4).

Major symptoms of gallbladder dyskinesia are epigastric pain and discomfort. Epigastric pain often develops after meals; it often assumes the form of repetitive intense pain. Patients complaining of this pain are not found to have abnormalities when examined by US, CT, upper gastrointestinal endoscopy or hematology test. Some patients receive invasive tests such as endoscopic retrograde cholangiopancreatography (ERCP) and arteriography because of repeated intense epigastric pain. However, it is not possible to make an accurate diagnosis of gallbladder dyskinesia by ERCP or arteriography. A definite diagnosis of gallbladder dyskinesia is only possible by tests capable of demonstrating gallbladder dysfunction such as cholescintigraphy. Cholecystectomy is the first choice method for the treatment of gallbladder dyskinesia. The percentage of patients whose symptoms disappear following this treatment is very high (5–7).

When used for the diagnosis of diseases involving morphological abnormalities (e.g., gallbladder stones, polyps and cancer), cholescintigraphy is much less useful than US or CT. For the diagnosis of gallbladder dyskinesia which involves gallbladder dysfunction, cholescintigaphy has been rated as the most useful modality and standard criteria for cholescintigraphy have been explored (8, 9). Gallbladder contractility, as evaluated by cholecystokinin (CCK) stimulated cholescintigraphy, is expressed as gallbladder ejection fraction. According to standard criteria, gallbladder ejection fraction below 35% is rated as evidently abnormal (10, 11). Cases with gallbladder ejection fraction below 35% are considered to be indicated for cholecystectomy and are highly likely to show disappearance of symptoms after this surgery (12–14). The safety of CCK stimulated cholescintigraphy has been established.

Fatty meal stimulated cholescintigraphy has been studied as a more physiological method of cholescintigraphy (15–17). Although fatty meal stimulated cholescintigraphy is not as accurate as CCK stimulated cholescintigraphy when used for measuring the gallbladder ejection fraction, its clinical usefulness has been demonstrated. CCK stimulated cholescintigraphy, which has become a standard test in Western countries, is not possible in Japan, since CCK has not yet been approved in this country. Therefore, when performing cholescintigraphy in Japan, fatty meal stimulated cholescintigraphy is recommended (17).

A disadvantage of cholescintigraphy is the necessity of injecting a radioisotope into the patient. For this reason, efforts have been made to develop a method of US capable of evaluating gallbladder contractility (18–21). Cholescintigraphy was slightly superior to US in many reports comparing the ability of diagnosing gallbladder dyskinesia between cholescintigaphy and US. CCK was often used in these studies, but some studies used compared fatty meal stimulated cholescintigraphy with US. If a method of US allowing evaluation of gallbladder ejection fraction is established, it will serve as an ideal means of diagnosing gallbladder dyskinesia since it does not necessitate radioisotope injection.

Gallbladder dyskinesia is difficult to diagnose even when ordinary means of diagnostic imaging such as US, CT, MR cholangiography and ERCP are employed. To allow accurate diagnosis of gallbladder dyskinesia, it is advisable to measure gallbladder ejection fraction by cholescintigraphy before invasive tests such as ERCP are performed.