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In vitro Study to Compare Stability and Homogeneity of Various Routinely Used Meals for Gastric Emptying Scintigraphy (GES) for Solids and Validating Radiolabeled Idli (Savory Cake) as an Improved Alternate Vegetarian Meal
Address for correspondence: Mr. Prathamesh Rajai, Department of Nuclear Medicine, Level 3, Green Zone, Medway Maritime Hospital, Windmill Road, Gillingham, Kent, ME7 1YJ, UK. E-mail: raj81sep@gmail.com
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Received: ,
Accepted: ,
This article was originally published by Wolters Kluwer - Medknow and was migrated to Scientific Scholar after the change of Publisher.
Abstract
Purpose:
The purpose of the study was to compare the stability and homogeneity of various routinely used meals for gastric emptying scintigraphy (GES) for solids and to validate an improved vegetarian well uniformly radiolabeled solid meal for GES, which is easily fully consumed by patients in view of their common symptoms in such indications and in keeping with Indian food culture.
Materials and Methods:
Following various types of solid meal preparations were labeled with 3 mCi of 99 mTc sulfur colloid (SC), and image of each meal was acquired on General Electric (GE) Infinia Hawkeye 4 camera: (1) Meal of 4 slice bread + 20 g butter with calorific value ≈ 356 kcal. (2) 4 slice bread + 30 g jam with calorific value ≈ 332 kcal. (3) 4 slice bread + 70 ml of milk with calorific value ≈ 243 kcal. (4) 150 g of sagu (sabudana) +5 ml refined vegetable oil + 10 g peanuts (sagu khichdi) with calorific value ≈ 324 kcal. (5) 4 idli + 2 tablespoon green chutney with calorific value ≈ 280 kcal. (6) 70 g wheat + 50 ml water + 5 ml refined vegetable oil with calorific value ≈ 237 kcal. (7) Meal of 75 g of idli mix + 80 ml water + 10 g butter with calorific value ≈ 310 kcal. All radiolabeled meals were subjected to the radiolabeled stability test procedure to calculate labeling efficiency which was compared.
Results:
Idli meal prepared with radiotracer added to the batter mixture itself, with a calorific value ≈ 310 kcal showed the highest uniform Tc99 m SC distribution in comparison to all other meal preparations.
Conclusions:
Radiolabeled idli (savory cake) prepared with radiotracer added to the batter mixture itself, appears to be an ideal vegetarian meal in comparison to all other meal preparations for gastric emptying scintigraphy studies, especially among patients with specific dietary restrictions.
Keywords
Gastric emptying scintigraphy
savory cake
sulfur colloid
Introduction
Gastric emptying scintigraphy (GES) is noninvasive and physiologic tool to measure gastric emptying time. GES typically assesses for gastroparesis in patients with postprandial symptoms of nausea, vomiting, abdominal pain, and/or early satiety and also provides important information in patients with esophageal reflux unresponsive to therapy or in diabetics with poor glycemic control to confirm or exclude delayed gastric emptying as a contributing factor to patient’s poor response to therapy.[1] In addition, GES is helpful in the assessment of patients with colonic inertia being considered for colectomy since individuals with concurrent delayed gastric emptying have a much lower response rate to surgery than those with normal GE.[2]
The reliable results of GES are dependent upon how efficiently the test meal is labeled with the 99 mTc-sulfur colloid. The components of a meal (size, digestibility, calories, and nutrient content) all affect the rate of gastric emptying. Solids and fats empty more slowly, whereas liquids, proteins, and carbohydrates empty more rapidly.[345]
Unstable labeling will result in the false/poor interpretation of GES. In India, the majority population being vegetarian, it was essential to validate a vegetarian radiolabeled solid test meal with equal or optimum labeling stability and homogeneity as that of standardized meal of egg whites.
Here, we studied seven different vegetarian-based solid meals, which comprised bread-butter, bread-jam, bread and milk, sagu khichadi, readymade idli with green chutney, chapatti or roti, and in-house cooked butter idli, assessed their homogeneity and compared their labeling efficiencies.
Materials and Methods
Various vegetarian-based radiolabeled solid meal preparations were assessed in this study, including in-house cooked idli (savory cake).
Labeling method of each of these meals
Following various types of solid meal preparations were labeled with 3 mCi of 99 mTc sulfur colloid (SC), and an image of each meal was acquired on GE Infinia Hawkeye 4 camera for 1 min per acquisition.
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Meal of 4 slice bread + 20 g butter with calorific value ≈ 356 kcal [Figure 1]
Figure 1 Acquisition of food article on the gamma camera, to see the distribution of the radiotracer99 mTc-SC (~3 mCi) sprinkled on the bread and then melted butter spread on the bread, and a sample was collected for counting when the butter was come back to semisolid state.
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4 slice bread + 30 g jam with calorific value ≈ 332 kcal [Figure 1]
99 mTc-SC (~3 mCi) sprinkled on the bread and then jam was spread on the bread.
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4 slice bread + 70 ml of milk with calorific value ≈ 243 kcal [Figure 1]
99 mTc-SC (~3 mCi) added to the paste bread and milk and well mixed with the spoon.
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150 g of sagu (sabudana) +5 ml refined vegetable oil + 10 g peanuts (sagu khichadi) with calorific value ≈ 324 kcal [Figure 1]
99 mTc-SC (~3 mCi) sprinkled at the end of preparation and well mixed with the spoon.
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4 idli + 2 tablespoon green chutney with calorific value ≈ 280 kcal [Figure 1]
99 mTc-SC (~3 mCi) sprinkled on the readymade idli (Savory cake) and the green chutney spread on the idli.
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70 g wheat + 50 ml water + 5 ml refined vegetable oil with calorific value ≈ 237 kcal [Figure 1]
99 mTc-SC (~3 mCi) was added to the dough of the chapatti/roti and then the dough was rolled and baked in the pan with oil.
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Meal of 75 g of idli (savory cake) mix + 80 ml water + 10 g butter with calorific value ≈ 310 kcal [Figures 2 and 3].
Figure 2 Labeling method to get uniform distribution of radiotracer in preparation of butter idli/savory cake
Figure 3 Labeling technique affects the uniform distribution of radiotracer99 mTc-SC (~3 mCi) was added to the batter of the idli and then the batter was transferred to the steamer for 15–20 min and removed from the steamer and allowed to cool for 5–10 min.
Radiolabel stability test
In-house labeled food articles were transferred onto a plate and allowed to cool at room temperature. A portion of the labeled food articles weighing about 10 g, was chopped into small pieces with the help of a metal fork to stimulate chewing. It was then transferred to 50 ml centrifuge test tube to measure the initial 99 mTc-SC content in the sample. Then, 10 ml of stimulated gastric fluid at PH 2.4 was added. The tube was placed in an incubator maintained at 37°C with in-between shaking the tube. After 1 h, the tube was removed and centrifuged for 2000 rpm for 2 min, resulting supernatant was transferred to another tube, and tube containing the crushed article was transferred to the dose calibrator to measure the activity of 99 mTc-SC still bound to the sample. After this, the supernatant was added back to the tube containing the sample, mixed well, and return to the incubator. The procedure was performed for a total duration of 4 h with the residual activity in the sample being measured at every 1-h interval in the dose calibrator. Using the initial 99 mTc SC activity in the sample as 100%, the percentage of 99 mTc-SC remaining bound to the sample after each 1-h interval was calculated. The appropriate decay correction factors were applied to the data.
The procedure was performed in triplet, and mean values were calculated. Sample labeling efficiency (SLE) % was calculated using the following formula,
% SLE = Sample count/total count × 100 [Table 1].
| Number | Food | Time | |||
|---|---|---|---|---|---|
| Labeling efficiency at 1 h (%) | Labeling efficiency at 2 h (%) | Labeling efficiency at 3 h (%) | Labeling efficiency at 4 h (%) | ||
| 1 | Idli-chutney | 89.3 | 74.53 | 69.2 | 61.45 |
| 2 | Khichadi | 82.3 | 76.9 | 73.7 | 65.15 |
| 3 | Bread butter | 83.2 | 81.2 | 72.8 | 66.6 |
| 4 | Bread milk | 77 | 73.5 | 69.8 | 68.4 |
| 5 | Bread jam | 96.2 | 83.9 | 81.3 | 79.2 |
| 6 | Chapatti/roti | 97.51 | 96.8 | 95.9 | 94 |
| 7 | Butter idli | 97.9 | 96.3 | 95 | 93.57 |
Homogeneity of radiotracer distribution
The acquired images were checked for homogeneity other than visual interpretation by dividing the images into two equal halves and calculating the percentage of the uptake in both parts [Table 2].
| Number | Food | Counts in ROI 1 (% uptake) | Counts in ROI 2 (% uptake) | Images showing the counting distribution | Interpretation |
|---|---|---|---|---|---|
| 1 | Idli-chutney | 31,146 (53) | 27,628 (47) |
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Percentage uptake shows almost uniform tracer distribution but visual interpretation shows nonuniform uptake with irregular uptake of activity |
| 2 | Khichadi | 116,146 (58) | 83,364 (42) |
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Percentage uptake shows nonuniform tracer but visual interpretation shows nonuniform uptake with irregular uptake of activity |
| 3 | Bread-butter | 28,320 (53) | 25,364 (47) |
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Percentage uptake shows almost uniform tracer but visual interpretation shows nonuniform uptake with irregular uptake of activity |
| 4 | Bread-milk | 63,882 (53) | 56,719 (47) |
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Percentage uptake shows almost uniform tracer distribution but visual interpretation shows uniform uptake |
| 5 | Bread-jam | 33,075 (58) | 23,580 (42) |
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Percentage uptake shows nonuniform tracer distribution and visual interpretation shows nonuniform uptake as well as with concentration of activity in the center |
| 6 | Chapatti/roti | 188,820 (71) | 76,263 (29) |
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Percentage uptake shows nonuniform tracer distribution and visual interpretation also shows nonuniform uptake with irregular uptake of activity |
| 7 | Butter idli | 29,050 (49.6) | 29,511 (49.4) |
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Percentage uptake shows uniform tracer distribution and visual interpretation also shows uniform uptake as well |
ROI: Region of interest
After quantitative and qualitative analysis, and comparing other factors including uniform distribution of the radiotracer, choice of the meal, and method of preparation, which are responsible for the efficient binding of radionuclide to the food particles or the meal, it was seen that 99 mTc-SC labeled chapatti/roti proved to be a better substitute to the egg white. It showed better radiotracer binding efficiency of 97.5, 96.8, 95.9, and 94% at 1, 2, 3, and 4 h, respectively, but it showed nonuniform tracer distribution. However, 99 mTc-SC labeled butter idli not only showed radiotracer binding efficiency of 97.9, 96.3, 95, and 93.57% at 1, 2, 3, and 4 h, respectively [Table 1], but also showed good uniform distribution of radiotracer [Table 2], thus suggesting it to be the best option as a substitute for egg white.[6]
Labeling method has high chances of contamination if appropriate care is not taken, and if the patient does not consume the whole meal, then that too may give erroneous results.
Discussion
Different methodologies were used for solid meal preparations at different imaging clinics (orange juice, cereal with milk, oatmeal, scrambled eggs, and chicken liver), and as a result, they often had different normal values. In 2007, an expert panel of gastroenterologists and nuclear medicine physicians met to decide on consensus standards for GES.
These recommendations were published in 2008. The standardized meal described in the GES guideline is a solid meal consisting of 0.5–1.0 mCi of 99 mTc-sulfur colloid scrambled with 120 g of liquid egg whites (Egg Beaters or generic), 2 slices of white toast, 30 g of strawberry jelly, and 120 mL of water.[7] It is recommended that this exact meal be utilized for all adult solid GES studies. The meal should be consumed within 10 min and imaging commences. In addition to standardizing the meal, the consensus guidelines released in 2008 standardized the imaging and interpretation, endorsing a protocol developed in 2000 by Tougas et al.[8] This simplified methodology for solid GES requires 1 min images to be acquired at only 4 time points: immediately after meal ingestion and at 1, 2, and 4 h with an optional fifth time point at 30 min which can be helpful in the assessment of rapid gastric emptying.
Factors that may affect the performance and negatively influence the clinical validity of a GES are:
Incomplete meal consumption
Slow meal consumption (taking longer than 10 min)
Vomiting a portion of the meal
Poor glycemic control
Meal content, fat, protein, acid, and osmolality
Volume, weight, caloric density, and particle size.
Gender and patient position (standing, sitting, and supine) metabolic state
Stress, exercise, and time of day.
If these problems occur, they should be included in the examination report as well as a comment as to their potential impact on the accuracy of the results.
Contraindications
Allergies to the recommended meal
Hypoglycemia (blood glucose level <40 mg/dL) and hyperglycemia in diabetics (blood glucose >250–275 mg/dL).[3]
It is highly important that the molecules of radiolabel should be uniformly distributed and remain tagged with the particles of solid during exposure to gastric fluid.[9] From the visual interpretation and result analysis, we can say that when radiotracer is added before cooking the meal, there is a uniform distribution of radiotracer is seen, like in meals chapatti and idli. Chapatti meal, however, showed nonuniform distribution as the dough, in which tracer is added is thick in consistency, and a homogeneous tracer mixture is practically difficult.
Tables 1 and clearly show that meal numbers 1–5, where Tc99m-SC was spilled over a cooked meal, did not involve exposure to heat/cooking after radiotracer was added which resulted in poor binding of tracer, nor could it spread uniformly.
Hence, it shows that the distribution is highly influenced by the method of preparation.
In comparison with idli and chapatti/roti, the rest of the other meals showed poor radiotracer labeling, which might lead to an inconclusive analysis of GES.
Our study is an in vitro comparison of meals, and further in vivo studies are encouraged with vegan idli meals and also head-to-head comparison of vegan meals with standardized nonvegetarian meals. Further studies for comparison of Tc99 m SC with other radiopharmaceuticals such as 99 mTc-tin colloid, 99 mTc-nanocolloid, and 99 mTc-MAA would also be interesting to know the impact of different radiotracers in GES.
Conclusions
Our comparative study concludes that the SLE of chapatti/roti meal and butter idli meal is good in comparison with other meals; however, the butter idli meal preparation shows good uniform distribution of radiotracer and can be used as an alternative meal to egg white. Other meals in comparison did not give the desired results for the solid gastric emptying study.
Conflicts of interest
There are no conflicts of interest.
Nil.
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