Assessment of gastric emptying by radio-nuclide study.
There is an increasing tendency to incriminate abnormalities in gastric emptying in the pathogenesis of gastroduodenal disease. In addition, there are many clinical situations e.g. dumping. in which detailed information about the pattern and rate of gastric emptying would be helpful in diagnosis. However, the available methods of measuring the rate at which food leaves the stomach are not entirely satisfactory.
Gastric emptying has been studied by noting the time taken for a radio-opaque meal to leave the stomach.,  Griffith described a method using radioactive chromium (Cr) with intermittent stomach scanning, which was found to be useful by others also.,  The new isotope technique avoids intubation. The counts can be taken at intervals of one minute, with the help of a computer. It was, therefore. decided to adapt this method to a suitably modified gamma camera which could enable easy, rapid and frequent observations.
Various types of meals, e.g. chicken liver, cornflakes, mashed potato and milk have been utilised for this purpose., , ,  In the present study, semisolid cellulose jelly labelled with mTc has been used.
Gastric emptying studies were conducted in a total of 30 individuals. To determine the range of normal gastric emptying time. ten individuals without any gastro-intestinal disease (controls) were studied. Ten patients with uncomplicated duodenal ulcer, ten patients with gastric outlet obstruction due to duodenal ulcer were also studied. In three patients from the last group, the study was repeated post-operatively. Of these 3 patients, 2 had vagotomy-pyloroplasty and one a highly selective vagotomy (HSV). Gastric outlet obstruction was confirmed by plain X-ray, saline load barium meal and fibre-optic endoscopy. None of the patients was receiving drugs known to influence gastrointestinal motility. Smokers were advised to abstain from smoking on the morning of the study.
Two hundred ml of liquid cellulose jelly was prepared and 200 micro-curie of mTc labelled sulphur colloid was added to it. The mixture was kept in a deep freezer till the jelly was semisolid.
After overnight fasting the patients were given the radionucleide-labelled jelly. The time of ingestion was defined as the midpoint of the period taken for consumption of the jelly. The patient was made to lie-supine and counts were treasured over the stomach by a gamma camera, at intervals of 1 minute for a period of 90 minutes. All counts were recorded with the help of medical computer system (MDS Computer with dynamic study). Ninety images were recorded. That the total count obtained was directly proportional to the radioactivity in the stomach was verified by scanning varying volumes of a solution of constant concentration in a dummy stomach of rubber, immersed in a tank of water.
With the help of the computer, each study was reviewed. In the first image all outline of the stomach was drawn over the image with the help of a dot pointer and 90 serial countings in this area were obtained from subsequent images. These were then plotted against time. The time taken for half the contents of the stomach to empty (T½) was determined in minutes and taken as a measure of gastric emptying.
[Figure 1] shows the results in the three groups.
In the healthy individuals (control group) the mean T½ was 61.2 minutes (range 52-71 minutes). In patients with duodenal ulcer without demonstrable obstruction. mean T½ was 64.2 minutes (range 53-78). In contrast, in patients with gastric outlet obstruction the mean T½ was 109 minutes. (range 98-142 minutes). This difference was statistically significant (p< 0.05). Gastric emptying time was delayed after HSV (T½ = 90 minutes) but was more, rapid after total vagotomy and pyloroplasty (T½ = 45 minutes).
Different methods have been developed to measure the rate of gastric emptying., , , , -, , 
Scintiscanning method (or gamma camera method) is based on the assumption that the emptying of the radioactive isotope chosen to label the meal represents the emptying of the meal itself. This is valid for a homogenous meal; hence a semisolid homogenous jelly was used for this purpose.
The choice of meal is always a subject of confusion. With milk, studies in vitro have shown that, in an acid medium, casein precipitates out, taking some of the radioisotope with it. If potato is used, salivary amylase has similar actions. Liquids alone empty more rapidly than a solid meal alone. We have used semisolid cellulose jelly. Hence gastric emptying rate can be measured with a single meal. An added advantage of jelly is that it is acceptable to vegetarian patients.
Various dilutions of a constant amount of mTc were scanned in the dummy stomach. The total external count was not affected. Consequently the addition of gastric juice or saliva to the labelled meal in the stomach would not affect the count.
The choice of radionucleide aims at minimizing the radiation dose to the patient and the efficiency of the isotope in producing gamma rays. We have used mTc technetium sulphur colloid which has a half life of 6 hours and which also fulfils the above criteria.
Results of gastric emptying studies have been expressed in diverse ways. The use of the half emptying time is convenient and this is an easily understood parameter. The use of a computer makes the study simple and accurate.
Our study is a preliminary report establishing this technique in assessing gastric emptying rate.
According to some workers, patients with duodenal ulceration show an increase in the overall rate of gastric emptying; Others,  find no such change. In our study, patients with duodenal ulceration had gastric emptying time similar to the control.
Our results of rapid gastric emptying after truncal vagotomy and pyloroplasty are in conformity with those reported earlier though our sample is small. After HSV, gastric emptying rate may be slowed but later returns to normal. In the present study also, gastric emptying was markedly slow following HSV.
It may be argued that the jelly which is semisolid outside may become liquid at body temperature but the values obtained in normal subjects in our study were similar to those reported in the western population with solid meals. Hence it can be inferred that semisolid cellulose jelly can be used as a single meal instead of liquids and/or solids. However, a further extensive research is necessary for establishing the diagnosis of borderline gastric outlet obstruction.