Gastric Emptying Imaging

Explain the purpose of a gastric emptying study

To assess gastric motility and rate of emptying into the small intestine.

Explain the structure and function of the stomach

A hollow, muscular organ that stores, mechanically and chemically digests as well as empties food into the small intestine.

Name these regions of the stomach

1. Pylorus

2. Antrum

3. Fundus

4. Body

Explain the structure and function of the fundus

The dome-shaped superior portion that initially holds food as it enters the stomach

Explain the structure and function of the body

The largest portion of the stomach that undergoes the majority of digestion

Explain the structure and function of the antrum

Distal portion of the stomach that undergoes grinding and propulsion.

Explain the structure and function of the pylorus

The terminal portion of the stomach that regulates gastric emptying into the duodenum

Name the 4 layers of the stomach wall

• Mucosa

• Submucosa

• Muscularis externa

• Serosa

Name the primary functional structures of the mucosa

Gastric pits

Explain the structure of the gastric pits

Pits within the mucosa containing specialised cells including, parietal, chief and enteroendocrine cells.

Explain the function of parietal cells

Secrete HCl and intrinsic factor required for B12 absorption

Explain the function of chief cells

Secrete pepsinogen which becomes pepsin when entering the stomach, chemically breaking down proteins.

Explain the purpose of the secretion of a thick, viscous gel containing bicarbonate

Lines the stomach, creating an alkaline barrier that neutralises gastric acid to prevent damage.

Explain rugae

The anatomical folding and ridges of the mucosa that allow the stomach to shrink and expand to accomodate for food.

Name these layers of the muscularis externa

1. Outer longitudinal layer

2. Middle circular layer

3. Inner oblique layer

List the clinical indications of gastric emptying studies

• Gastroparesis

• Dumping Syndrome

• Functional Dyspepsia

• Nausea/vomiting/bloating symptoms

• Pre/post surgery

• Reflux

Define gastroparesis

Delayed gastric emptying

Define dumping syndrome

Rapid gastric emptying

Define functional dyspepsia

A gut-brain disorder causing upper abdominal pain and early satiety with no structural abnormalities.

Name the 2 types of reflux

• GERD - gastroeosophageal reflux disease

• Silent/laryngopharyngeal reflux

Explain patient preparation for gastric transit studies

• Fasting for at least 6 hours

• Cease prokinetics for 24 hours

• Cease opiates and antispasmodics for 48 hours

State the BSL that diabetics must meet before gastric emptying studies

Between 4-11mmol/L

Explain why diabetic patients BSL must be between 4-11mmol/L

• <4mmol/L - symptoms and imaging can mimic dumping syndrome

• >11mmol/L - symptoms and imaging can mimic gastroparesis

Define prokinetics

Medications that enhance GIT motility

Define opiates

Medications that delay gastric emptying

Define antispasmodic agents

Medications that relax smooth muscle

Name the 3 most common RPs for gastric emptying studies

• 99mTc Colloids - solid meals

• 99mTc DTPA - liquid meals

• 99mTc MAA - patients with sulphuric allergies

Name the dose for gastric emptying studies

40 MBq

Explain the standard meal for gastric emptying studies

• 2 egg whites scrambled with the RP

• 2 pieces of bread with jam

• 1 glass of water

Explain the meal for patients allergic to eggs

Packet of instant oats mixed with water and the RP

Explain why eggs and porridge are used as standard meals

Allows the RP to be physically incorporated into the protein matrix as it cooks and solidifies, remaining bound to the food during emptying.

Why are eggs preferred

Because the greater protein content allows for stronger binding to the protein matrix.

Explain the liquid meal for gastric emptying studies

1 glass of water mixed with the RP

Explain the camera and patient positioning for gastric emptying scans

Camera positioned for anterior and posterior acquisitions as the patient is positioned supine

Explain the imaging parameters for gastric emptying studies

• Static 2 min images at T0 and every 30 mins for up to 4 hours

• 128 × 128 matrix

Explain image processing for gastric emptying studies

• Apply ROI around stomach at each time point (anterior and posterior)

• Calculate geometric mean and use to create TAC with trendline

• Calculate half-clearance time

State the normal range of half-clearance time using a standard meal

44-110 mins

State normal % retention of standard meal

<10% after 4 hours

State 2 types of abnormal % retention of a standard meal

• Rapid emptying - <10% after 2 hours

• Delayed emptying - >10% after 4 hours

Explain lag time and how it appears on a TAC

An initial plateau or shallow slope after ingestion in which food is held in the fundus and no gastric emptying occurs