Technegas-labelled brown rice, and water as physiological non-absorbed gastric markers
WM Burch, RJ Browitt, DE Crellin et al
The idea to use Technegas as a gastric marker arose from a simple experiment performed in 1986 to assess the inert nature of the particles if swallowed during a ventilation manoeuvre. A conical flask containing a small quantity of water was filled with Technegas directly from the generator, vigorously shaken for two minutes and then drunk. From gamma camera observations over a 24 hour period it was clear that no activity had been absorbed from the gut as the residual activity in the lower abdomen before defecation was effectively the same, after correction for decay, as that measured in the stomach immediately following the drink.
A variety of food stuffs have been tried by nuclear medicine laboratories over many years in attempts to find an optimum palatable combination which was simple to prepare in any nuclear medicine department. It must be remembered that the process of labelling food contravenes a basic radiation protection tenet banning eating and drinking in radiation control areas, and this also highlights the need for a simple process to minimise the conflict.
Most labelling is based on egg or dairy products, which are not suitable for all patients for ethnic, religious or simply allergy reasons, and in which the label is not always well bound. Wholemeal rice was selected for this project as it is a universal food acceptable to all cultures, can form the basis of a flavoursome meal, has large enough particles to require the milling action of the stomach - thus demonstrating the characteristic lag phase of solid food processing - and is easily standardised. The calorific content of a 100g portion is 360kcal ( 1508kJ ). If 10g of sugar or honey is added for flavour, the calorific value increases by about 10%.
The nature of Technegas particles is more fully described on another page Nature of Technegas. They form a sub-class of substances originally known as "metallo-fullerenes", but now classified by chemists as nanophase composite materials. The name "FullerTag®" has been registered specifically to describe this kind of radio-labelled species. Upon ingestion, whether in food or drink, the particles remain totally inert, passing without any measurable absorption right through the gastro-intestinal tract. In a preliminary trial on seven subjects, whether they ate labelled rice or drank FullerTag® in water, blood samples taken at 2 hours following ingestion showed a maximum of 3% of the total activity, which represents the normal level of Pertechnetate found in a standard Technegas sample under routine production conditions. Autoradiography has shown uniform binding of the Technegas particles around the membrane of the rice grain.
We have designed a collection system which is based on standard electrostatic trapping principles, and is in excess of 90% efficient at trapping FullerTag® on a stainless steel wire- mesh electrode coated with salt and a biologically compatible surfactant. Within five minutes of generation, an entire batch of Technegas can be trapped on the electrode which is rinsed in about 1ml water to remove the coating and FullerTag®. The water suspension is either added to a glass of water to form a 250ml drink, or dispersed into a cooking pot with boiling water and 100g of brown rice and cooked for 30 minutes. At the conclusion of cooking, the rice is washed in hot water to remove activity not bound to the grains; spiced or sweetened to taste; then eaten by the patient under study. Alternatively, the patient drinks the labelled water for a pure liquid emptying examination. Note that for good reproducibility, it is important to keep both the calorific content of the meal and the volume constant for each patient. The meal or drink is first checked for activity under the gamma camera - about 50MBq gives sufficiently short imaging times and statistics for gastric emptying studies and delivers a whole body dose of about 10mSv to the patient. Immediately after consumption of the rice or water, the patient is positioned under a gamma camera in the recumbent position, the camera viewing the abdomen anteriorly. Data is collected for 90 minutes at 1 minute intervals (Fig.1).
Before commencing the last frame, a position marker is placed on xyphisternum. At the end of the dynamic collection period, the camera is rotated to the left lateral position, and with the marker still in position, a single image is obtained. Further spot images may be obtained as the activity progresses through the GI tract ultimately leaving a faint trail of activity outlining the colon after the main bolus has reached the rectum (Fig.2).
Following a standard software protocol routine, the raw data are analysed and presented as clearance curves, or simply as half-time figures, and compared with charts of known normal function (Fig.3).
This work was validated and extended by a group under Michael Horowitz, Professor of Gastroenterology at the University of Adelaide (Biblio ref #153).