Gastric Emptying Scintigraphy

6.4.1 Radiopharmaceutical

• ^99mTc-sulphur colloid

6.4.2 Uptake mechanism / biology of the tracer

The test-meal used for scintigraphic GE consists of an egg-white meal in the form of a well-cooked omelette:

• After separation of the white and the yolk of one or two eggs, the ovalbumin is labelled with 18-37 MBq of ^99mTc-sulphur colloid;
• Egg white and yolk are then mixed together to obtain an omelette mixture and a homogeneous radiopharmaceutical distribution;
• This omelette must be well cooked to ensure a strong ovalbumin binding and radiolabelling stability for several hours in an acidic and pepsin gastric medium.
• Cooking causes a conformational change in albumin around the molecules of ^99mTc-sulphur colloid that is entrapped within a molecular albumin cage.
• The omelette is served with toast, jam, and water, and sometimes with orange juice.

The same test-meal must be prepared for all patients and for repeated evaluations [102].

6.4.3 Indications

• Dyspeptic syndromes:
  • Positive diagnosis and quantification of dyspeptic syndromes;
  • Monitoring of prokinetic treatment efficacy.
• Diabetic gastroparesis:
  • Positive diagnosis;
  • Role of a possible diabetic gastroparesis in diabetes instability.
• Gastro-oesophageal reflux with dyspeptic syndrome:
  • Ineffective anti-reflux treatment;
  • Preoperative Assessment.
• Complications of gastric surgery including dyspepsia diagnosis and monitoring of Dumping syndrome.
• Objectification of digestive tract motor impairment in some systemic diseases (such as scleroderma).
• GE disorders observed in irritable bowel syndromes, chronic liver disease.
• (alcoholic cirrhosis and post-hepatitis), hypothyroidism, X syndrome (hypertension, obesity, resistance to insulin, dyslipidaemia) (this is a non-exhaustive list).
• Heart-lung and kidney-pancreas transplants before and/or immediately after transplantation to guide replenishment.

6.4.4 Contra-indications

• Allergy to eggs. (alternatively: use porridge test-meal or pancake test-meal)
• Pregnancy.
• It is not recommended to interrupt breast feeding although an interruption of 4 h during which one meal is discarded can be advised to be on the safe side [3].

6.4.5 Clinical performances

Since the symptoms of rapid or delayed GE are similar, but treatments quite different, GE scintigraphy should be able to identify both rapid and slow GE using a quantification of gastric retention at several time points.

• Normal retention rates are ≤90% at 1 h, ≤60% at 2 h, and ≤10% at 3h/4 h.
• Delayed GE is determined for retention rates higher than those defining a normal GE, especially for late 2h and 3h/4h time points.
• A retention <30% at 1h is indicative of rapid GE.

There is no close correlation between GE delay and symptoms occurrence. However, grading for delayed GE severity should be based on the 3h/4h gastric retention rate; grade 0 (normal): <10%; grade1 (mild): 11-20%; grade 2 (moderate): 21-35%; grade 3 (severe): >35%.

The normal GE after surgery in patients with partial gastric resections, post bariatric surgery, and different drainage procedures is not known. Liquid GE test is generally not clinically useful, except maybe in these cases to objectify for instance a Dumping syndrome.

GE scintigraphy allows physiological and separate analysis of proximal (fundal) and distal (antral) functions.

6.4.6 Activities to administer

For adults, the recommended administered activity ranges from 18-37 MBq.

In paediatric nuclear medicine, the activities should be modified according to the EANM paediatric dosage card (https://www.eanm.org/publications/dosage-calculator/).

6.4.7 Dosimetry

The effective dose per administered activity is [3]:

• ^99mTc-sulphur colloid: 9.1 µSv/MBq

The range of the effective doses for the suggested activity (normal liver condition) is 0.16-0.34 mSv.

Caveat

“Effective Dose” is a protection quantity that provides a dose value related to the probability of health detriment to an adult reference person due to stochastic effects from exposure to low doses of ionizing radiation. It should not be used to quantify the radiation risk for a single individual associated with a particular nuclear medicine examination. It is used to characterize a certain examination in comparison to alternatives, but  it should be emphasized that if the actual risk to a certain patient population is to be assessed, it is mandatory to apply risk factors (per mSv) that are appropriate for the gender, the age distribution and the disease state of that population."

6.4.8 Interpretation criteria/major pitfalls

Patient factors to be considered before interpretation include:

• Medications that delay GE such as opiates and anticholinergic antispasmodic agents;
• Medications that accelerate GE such as Prokinetics;
• Tobacco smoking that may slow GE;
• Hyperglycaemia that can delay GE.

The meal composition is the most important variable. The same test-meal needs to be given to all patients and in case of repeated assessments in the same patient.

Patient results must be compared to normal values established in healthy volunteers using the same test-meal.

Incomplete meal ingestion or vomiting after the initial baseline image can lead to values suggesting more rapid emptying.

6.4.9 Patient preparation

Any medication which affects gastrointestinal motility (e.g. metoclopramide, domperidone, cimetidine, parasympatholytics and sympathomimetics) should be discontinued for 3 days before the investigation unless the requesting physician wishes to investigate the effect of these prokinetic agents.

The test should be performed in the morning after an overnight fast (at least 6 h).

No smoking before and during the test.

Blood glucose of diabetic patients before the beginning of the test should be <3 g/L

(<17 mmol/L). Diabetic patients should self-administer their insulin at half-dose just before the test-meal.

6.4.10 Methods

Acquire anterior and posterior views at 0, 1, 2, and 4 h after meal ingestion. Images may be obtained with the patient standing, sitting or supine, but position should not change during the study. Normal values must be established in the position used (must have separate normal values for upright and supine positions).

Determine gastric retention rate by computing geometric mean activity of decay-corrected counts (square root of the product of the anterior and posterior counts) at each imaging time.

Curve fitting of geometric mean values over time (TACs) provide useful information on GE and allows the computation of reliable and reproducible parameters that reflect the whole GE process, such as half emptying time (T50), time of lag phase and time of real emptying time (gastric emptying with a constant rate).

A dual isotope study (using 4 MBq 111In DTPA in 200 ml water or orange juice in addition to the solid test meal) can be carried out if the gastric emptying of a liquid is to be investigated at the same time. In certain circumstances, for example in some diabetic patients, gastric emptying of a solid meal may be abnormal whilst that of a liquid (or semi-solid) meal can be normal. After vagotomy, gastric emptying of liquid components is often too rapid whilst that of solids is delayed or normal.