gastrointestinal scintigraphy

what organs does the gastrointestinal system consist of? (8)

teeth, tongue, oesophagus, stomach, spleen, pancreas, liver, colon

what nuclear medicine scans can be done to investigate the gastrointestinal tract? (6)

1. oesophageal swallow

2. gastric empty

3. colonic bowel/intestine transit

4. gastrointestinal bleed

5. Meckel’s Diverticulum

6. Tenckhoff study (peritoneum)

what are the organs found in the alimentary canal/gastrointestinal tract? (4)

• oesophagus

• stomach

• small intestine/small bowel

• large intestine/large bowel/colon

what are the accessory structures of the gastrointestinal system? (5)

• tongue

• salivary glands

• liver

• spleen

• pancreas

what are the 4 layers of the gastrointestinal tract?

1. mucosa

2. submucosa

3. muscularis

4. serosa

what is the mucosa layer of the gastrointestinal tract?

• innermost layer

• allows secretion of mucus, hormones, digestive enzymes, absorption of digestive end products

• protects against infection

• contains villi - part of epithelium

what is the submucosa layer of the gastrointestinal tract?

• second innermost layer

• dense connective tissue

• lymph, blood vessels, lymphoid follicles, nerves

• supplies GIT tissue with blood

what is the muscularis layer of the gastrointestinal tract?

• third innermost layer

• circular muscle

• longitudinal muscle

• inside serosa

• inner sheet of circular smooth muscle

• outer sheet of longitudinal muscle

what is the serosa layer of the gastrointestinal tract?

• outermost layer

• part of visceral peritoneum

what are the intrinsic nerves of the gastrointestinal tract, and what nervous system are they part of? (2)

enteric nervous system

1. myenteric plexus

2. submucosal plexus

what is the myenteric plexus of the gastrointestinal tract?

• myenteric plexus controls muscularis layer - involved in GI tract motility

  • able to control frequency and strength of contractions

what is the submucosal plexus of the gastrointestinal tract?

• submucosal plexus has motor neurons

  • supply secretory cells of mucosa

• sensory neurons in mucosa epithelium

• chemoreceptors and mechanoreceptors - stretch receptors

  • provide feedback

what occurs to the gastrointestinal tract due to parasympathetic and sympathetic nervous system?

Parasympathetic nervous system

• increase GI secretion and motility by increasing activity of ENS neurons

Sympathetic nervous system

• inhibit ENS neurons, decrease GI secretion and motility

  • response to emotions such as anger, fear, anxiety

what are the basic functions of the digestive system? (5)

1. ingestion

2. movement of food (motility)

   • down the oesophagus, inside stomach, through bowel

   • peristalsis

3. digestion - mechanical and chemical

4. absorption - passage from GIT into CVS and lymphatic system

5. defecation - elimination of indigestible substances

what is mechanical digestion?

• preparing food to be chemically broken down

• physical preparation of ingested food for chemical digestion

• chewing

  • cutting and grinding with teeth

  • tongue mixing food with saliva

• churning food in stomach (chyme)

• segmentation

  • rhythmic local constrictions of intestine

  • mixes food with digestive juices

what is chemical digestion?

complex molecules broken down into chemical building blocks by enzymes

how does chemical digestion of proteins work?

• pepsin in stomach breaks proteins into smaller molecules

• pancreatic and brush border enzymes in small intestine/bowel break these molecules down into amino acids

how does chemical digestion of carbohydrates work?

• digestion starts in mouth (amylase → starch) and continues in small intestine/bowel

• complex carbohydrates (starch, sucrose, lactose, maltose, glycogen) are split into simple sugars (glucose and fructose) by pancreatic and brush border enzymes

how does chemical digestion of lipids work?

• bile comes from gall bladder, emulsifies fats and oil globules into smaller droplets

• lipases from pancreas break down triglycerides into fatty acids and monoglycerides

what is the oesophagus, and what is its function?

• secretes mucus and transports food to stomach

• no digestive enzymes or absorption functions

• transport only

• 20-30cm long in adult

• hollow muscular tube

• between swallows the oesophagus remains closed (collapsed)

  • when swallowing food the lumen distends up to 2cm anteroposteriorly and 3cm laterally

how is the oesophagus innervated?

• 3 phases of swallowing controlled by central pattern generated circuitry of the brain stem, and the peripheral reflexes

• oral, pharyngeal and oesophageal phases of swallowing are independent of each other

  • central pattern generators of the brain stem control timing of the phases

  • peripheral manifestation of these phases depend on sensory feedback through reflexes of the pharynx and oesophagus

  • dependence of oesophageal phase of swallowing on the peripheral feedback system explains its absence through failed swallows

  • reflexes that initiate pharyngeal phase of swallowing also inhibits oesophageal phase

    • ensures appropriate timing so that food bolus is transferred - prevents occurrence of multiple oesophageal peristaltic events

    • inhibitory reflexes are probably partly responsible for patients that have trouble swallowing

what brain stem nuclei are involved in the different phases of swallowing?

• three separate sets of brain stem nuclei that mediate oral, pharyngeal and oesophageal phases of swallowing

  • trigeminal nucleus and reticular formation probably contain oral phase pattern generated neuron circuitry

  • nucleus tractus solitarius (NTS) probably contains second sensory neurons and the circuitry for the pharyngeal and oesophageal phase of swallowing

  • nucleus ambigus and the dorsal motor nucleus contain the motor neurons that are responsible for pharyngeal and oesophageal phases of swallowing

  • ventrimedial nucleus of NTS may govern coupling of pharyngeal phase to oesophageal phase of swallowing

what are the three phases of swallowing?

1. voluntary

2. pharyngeal

3. oesophageal

what is the voluntary phase of swallowing?

first phase

food is placed at back of mouth and rolled into pharynx

what is the pharyngeal phase of swallowing?

• second phase

• trachea is closed and oesophagus is open

  • oesophagus is generally closed, only opens when food is passing through

  • fast peristaltic wave forces bolus of food down into upper oesophagus

    • takes a couple of seconds

  • in response to that, peristalsis keeps food moving down oesophagus in response to swallowing and stretch receptors in oesophagus

what is the oesophageal phase of swallowing?

• final phase

• transfer food rapidly from pharynx to stomach

  • peristalsis and gravity combine to force food into stomach

what muscles/sphincter make up the oesophagus? (2)

• upper third is striated muscle

• lower two thirds is smooth muscle

• lower oesophageal sphincter found at the end of the oesophagus before the stomach

what are the oesophageal transit times for solids and liquids?

• solids

  • between 4-8 seconds to traverse the oesophagus

• liquids

  • between 1-2 seconds to traverse the oesophagus

how can brain/cranial nerve issues cause oesophageal motility disorders?

innervation of the oesophagus is connected to the brain/brain stem

how can diabetes cause oesophageal motility disorders?

• diabetes can cause nerve degeneration

  • causes issue with motility

    • controlled by muscles

how can systemic sclerosis cause oesophageal motility disorders?

• systemic sclerosis (smooth muscle degenerates) causing diminished contractile force

  • smooth muscle inside oesophagus doesn’t function as well

what are primary disorders of oesophageal motility?

include dysfunction of upper oesophageal sphincter and disorders resulting from abnormalities of the nerve supply to the oesophagus

what are secondary disorders of oesophageal motility, and what are examples?

• caused from other diseases interfering with anything involved in function of oesophagus

• includes tumours, gastro-oesophageal reflux, spasm, diabetes mellitus, connective tissue disorders

  • systemic scleroderma is the most common of these

  • scleroderma (aka systemic sclerosis) is a chronic autoimmune disease

    • causes fibrosis of the skin and some internal organs

      • oesophagus, lungs, kidneys, heart

  • in oesophagus, affecting the lower 2/3’s smooth muscle portion

  • three times more likely in females than males

what are clinical indications of oesophageal pathology? (5)

1. dysphagia

2. odynophagia

3. heartburn

4. regurgitation

5. haematemesis

what is dysphagia?

conscious bolus arrest during swallowing, unable to swallow properly

what is odynophagia?

pain upon swallowing

what is regurgitation?

passive retrograde flow of stomach contents back up the oesophagus

what is haematemesis, and how can it relate to oesophageal pathologies?

the vomiting of blood, can indicate ruptured varices or ulceration

what is gastro-oesophageal reflux, and what can it lead to?

• occurs when contents of stomach pass back through gastro-oesophageal junction and into oesophagus

• heavily dependent on integrity of lower oesophageal (cardiac) sphincter

• acid film left behind is neutralised by swallowed saliva

• reflux can lead to oesophagitis, heart burn, strictures, ulcers and pulmonary aspiration

what is achalasia, as an oesophageal motor disorder?

• smooth muscle of lower oesophagus fails to relax

• unknown aetiology

• peristalsis is ineffectual in the lower 2/3 of the oesophagus and cardiac sphincter (lower oesophageal sphincter) remains contracted

  • food enters lower oesophagus but cannot pass further

what is a diffuse spasm as an oesophageal motor disorder?

• normal peristalsis up to the mid to distal portion where wave progression disobedience and tertiary contraction takes place

• sphincters are rarely involved but achalasia may result

what are the four regions of the stomach?

1. cardia

2. fundus

3. body

4. pyloric part

what is the cardia region of the stomach?

near the lower oesophageal sphincter/cardiac sphincter

what is the fundus of the stomach?

top part of the stomach

what is the body of the stomach?

middle of the stomach

what is the pyloric part of the stomach?

end part of the stomach, also contains pyloric sphincter passing into duodenum

what are the functions of the stomach? (4)

• to mix saliva, food and gastric juices to form chyme - form that the food now takes

• serves as reservoir for food before release into small intestine

• secretes gastric juice which contains HCl (kills bacteria and denatures proteins), pepsin (begins digestion of proteins), intrinsic factor (aids digestion of B12) and gastric lipase (aids digestion of triglycerides)

• secretes gastrin into blood

what is gastrin and gastric acid?

• gastrin is a hormone the stomach makes to fuel the release of gastric acid, needed to digest and absorb nutrients, breaking down proteins and amino acids

• stomach makes 2-3 litres of acidic fluid a day

• gastric acid is found inside g cells found in stomach lining and upper small intestine.

what is the vagus nerve, and what can occur if damage/removal occurs?

• vagus nerve supplies innervation to stomach

  • damage results in no peristaltic contractions after meal

  • supply from anterior or posterior vagus nerve - some contraction

  • vagotomy - complete removal of vagus nerve results in no emptying

how can changing tonic pressures in the proximal stomach affect gastric emptying?

• diminished tonic pressure → delayed gastric emptying

• increased tonic pressure → accelerated gastric emptying

how can peristaltic waves in the distal stomach affect gastric emptying?

diminished frequency or amplitude of peristaltic waves → delayed gastric emptying

how can coordination between stomach and duodenum affect gastric emptying?

no coordination between stomach and duodenum → delayed gastric emptying

how can tone or phasic contractions to the sphincter in the pylorus affect gastric emptying?

• if there is no tone to the sphincter in the pylorus, there will be accelerated gastric emptying

  • increased tone or phasic contractions → delayed gastric emptying

how can changing receptive relaxation in the proximal duodenum (duodenal bulb) affect gastric emptying?

• diminished receptive relaxation → delayed gastric emptying

• increased receptive relaxation → accelerated gastric emptying

how can contractions in the duodenum affect gastric emptying?

• excessive number of segmental contractions → delayed gastric emptying

• excessive number of peristaltic contractions → accelerated gastric emptying

what is the process of food entering and exiting the stomach? (4)

1. filling: food enters stomach

   • between 50ml and 1.5L

2. storage: food can be stored in fundus without mixing

3. mixing: peristaltic waves propel chyme towards pyloric sphincter

   • sphincter gets contracted so chyme is tossed back into stomach, mixing back and forth

4. emptying: rate is influenced by degree of stomach distension and filling

   • increased amounts of fat, acid, osmolarity and distension in the duodenum decreases gastric emptying

   • local nervous reflexes and hormones secretin and CCK inhibit emptying

what are common causes for delayed gastric emptying? (5)

1. muscle disorders

   • systemic sclerosis (scleroderma)

   • systemic lupus erythematosus (autoimmune disease affecting connective tissue)

   • amyloidosis (deposition of amyloid proteins in organs causing harm)

2. post surgical

3. extrinsic nerve diseases

   • most commonly neuropathy associated with diabetes mellitus

4. reflux disease

5. anorexia nervosa

what are medications that delay gastric emptying? (6)

1. opiates - pain relief

2. antidepressants

3. cholecystokinin

4. progesterone

5. calcium channel blockers

6. levodopa

what are medications that increase gastric emptying rate? (5)

1. metoclopramide

2. domperidone

3. erythromycin

4. motilin

5. laxatives

what are the symptoms of delayed gastric emptying? (5)

symptoms are poorly defined and non specific

1. upper GI tract dyspepsia

   • post prandial discomfort

   • bloating

   • nausea

2. dyspepsia with no anatomical cause

3. dyspepsia with no response from acid suppressants

4. identified diabetic with poor glycaemic control

5. gastroparesis

   • mild paralysis of stomach

what is dyspepsia?

(indigestion)

• post prandial discomfort

• uncomfortable feeling of fullness

• heartburn

• bloating

• nausea

• many sufferers exhibit delayed emptying

what are the three sections of the small intestine?

1. duodenum

2. jejunum

3. ileum

what are the starting and ending points of the small intestine?

• commences at pyloric sphincter in stomach

• extends to ileocecal valve where it joins large bowel

what is the duodenum?

• extends around 25cm

• wraps around head of pancreas

• shortest stretch of GIT but most active

• includes hepatopancreatic ampulla aka Sphincter of Oddi

  • entrance of pancreatic enzymes and bile

• chyme mixes with bile, enzymes and mucus

  • digestion of bulk of carbohydrates, fats and proteins

  • some absorption

what is the jejunum?

• 2.5m long

• middle portion of small intestine

• slightly larger diameter than duodenum, more folds and villi

• site of absorption for amino acids, glucose and fatty acids from digestion in duodenum

• site of absorption for vitamins and minerals

what is the ileum?

• last section of small intestine/bowel

• terminates at caecum

• site of vitamin B12 absorption (IF receptors)

• absorbs products of digestion not yet absorbed by jejunum

• absorbs bile salts

• common site for Meckel’s diverticulum

• hangs loosely coiled in abdomen, fixed to abdominal wall by fan shaped mesentery

what is the main function of the colon?

• absorb water and electrolytes

• requires maximising surface contact and a slow transit of contents

• defecate, removing waste in the form of faeces

what does the colon/large bowel consist of? (6)

• caecum

• ascending colon

• transverse colon

• descending colon

• sigmoid colon

• rectum

what is Haustra?

• bands of smooth muscle which ‘pucker’ to form small pouches within colon

  • not seen in other parts of GIT

• help to propel waste through colon

what is diarrhoea?

• increased bowel movement

• increase in fluidity of faeces

• not a common indication for colonic transit studies

• often associated with other symptoms

  • abdominal pain, fever, rectal bleeding, dehydration, malabsorption

• classified into four major types

  • exudative, osmotic, secretory and dysmotility

what are the most common causes of diarrhoea? (4)

1. IBS (irritable bowel syndrome)

2. lactose intolerance and other dietary conditions

3. inflammatory bowel disease

4. colon cancer

what is IBS?

• IBS is not a disease, it is a group of symptoms that occur together

  • GI tract does not become damaged

• symptoms include abdominal pain or discomfort, cramping and diarrhoea or constipation, or both

• most studies indicate between 10-15% of the population suffers IBS

  • affects twice as many women as men

  • often found in people younger than 45

• most sufferers do not seek medical advice or intervention

• no known organic cause

what is constipation?

• a symptom, not a disease

• defined as less than three bowel evacuations per week

• chronic constipation can be

  • idiopathic

    • low transit constipation (neurogenic affecting ENS)

    • dyssynergic defecation (lack of coordination between pelvic floor muscles)

    • normal transit constipation (functional constipation or IBS with constipation)

  • secondary to drugs (opiates such as morphine)

• severe constipation can cause faecal impacting

  • lead to bowel obstruction → life threatening

what is the patient preparation for oesophageal swallow study?

• overnight fast

• rehearse swallow procedure

  • practice with plain water first

• find out medication

what is the radiopharmaceutical used for oesophageal swallow, and what is the dose?

• 99mTc colloid in water

• some departments also use a small amount of bread/eggs and perform solid oesophageal transit

• use milk if children, no dairy allergies

• 4x10mL aliquots (~10MBq each)

how is the radiopharmaceutical administered for oesophageal swallow?

• oral using syringe and mixing cannula

• squirt 10mL into mouth with blunt cannula, do not swallow yet

• count to 3 and then swallow

• do not swallow again until image is finished

• if doing multiple times, get multiple doses ready

what is the imaging procedure for oesophageal swallow?

• 2 erect and 2 supine images

  • child additional lateral and prone

• FOV anterior and posterior chest

  • mouth at top, stomach at bottom

• 40x1 sec anterior and posterior dynamic

• 64x64 matrix

• do not re swallow during acquisition

  • need to coach the patient through this

if patient has reflux/vomiting issues lying down, do one supine and one erect

we need to watch the food travel all through the oesophagus into the stomach

what is the image processing for oesophageal swallow?

• generate time activity curves for each acquisition

• divide oesophagus into thirds

  • upper, mid, lower

what is the image interpretation for oesophageal swallow?

abnormal studies show less than 90% clearance over 15 seconds

no activity by 15 seconds = normal oesophageal transit

what is lag time?

• as solid food enters the stomach, it pauses in the fundus to be partly digested

  • early digestion occurs through acidic and turbulent motion

• the pause can be imaged as a lag phase

• the lag phase is followed by linear emptying of solid food into the duodenum

• food composition affects lag time

  • after this, emptying rates are equivalent

  • liquid tracers do not experience lag time, emptying commences immediately

what is the patient preparation for solid gastric emptying?

overnight fast

• don’t eat something that morning

  • system would already have been activated, not as accurate imaging

• cease caffeine/nicotine, can affect emptying

• cease motility drugs, antinausea drugs

• cease stomach medications

patient should eat the whole meal in 10 minutes, all must be in the stomach together

check for allergies, assess symptoms, determine what they can eat

what is the radiopharmaceutical and what is the activity for solid gastric emptying?

• 99mTc colloid in scrambled egg

• egg whites most important

  • colloid binds to protein in whites

• porridge and milk if allergic to eggs

• 40MBq

• administered orally as a meal

what is the patient position and field of view for solid gastric emptying?

supine, upper abdomen FOV

• erect if needed

  • repeat studies with short acquisition times

what are the imaging parameters for solid gastric emptying?

• simultaneous anterior and posterior acquisitions

• planar for solids, dynamic for liquids

  • planar: 2 minute images every 30 minutes or 1 hour for 4 hours (starting at T0)

  • dynamic: 2 minutes/frame for 2 hours (starting at T0)

  • matrix 128 x 128

• if dynamic, make sure they don’t sleep

  • sleeping can slow gastric empty time

how are gastric emptying images processed?

1. generate regions of interest (ROI) over stomach

   • at each time point for anterior and posterior images

2. determine and apply geometric mean

3. correct counts for radiation decay at each time point

4. time activity curves are produced

5. determine half clearance time

   • time it takes for stomach to clear half its contents

why is geometric mean used for gastric emptying?

• the fundus (top) is more posterior than pyloric region (bottom)

• activity sitting in fundus is attenuated more on anterior views than activity in pyloric region

  • in posterior images, reverse is true

• the geometric mean compensates for attenuation of activity

  • collected as counts in the respective ROIs, originating in the stomach for each of the anterior and posterior views

what are the normal and abnormal finds for solid gastric emptying using scrambled eggs

Normal findings

• the half clearance time is around 90 minutes - for scrambled eggs

Delayed gastric emptying

• the half clearance time is >> than 90 minutes for scrambled eggs

• important that the department is consistent with choice of food

• changing food material introduces new variables and sources of error

what are the indications for small intestine/bowel transit studies?

• when symptoms of bloating, early satiety, dyspepsia and nausea after eating are followed with post prandial diarrhoea

• typically performed with gastric emptying study and/or colonic transit study

• no medicare code for small bowel transit

  • need to add it to another study to be paid for it

what is the radiopharmaceutical for small bowel transit imaging?

67Ga colloid in water or 99mTc

what is the patient positioning and field of view used for small intestine/bowel transit imaging?

supine, anterior and posterior abdomen FOV

what images are acquired for small intestine/bowel transit imaging?

• planar imaging at 2, 3, 4, 5, 6 hours post ingestion

• 5-10 minutes each, 128x128 matrix

  • if you are linking to colonic transit, keep time consistent

how are small bowel transit images processed?

• no quantitative analysis is usually performed on small bowel transit

• average emptying time is 280 minutes for solids

  • range 240-320 minutes

• accelerated small intestine/bowel dysmotility may be revealed in patients with

  • functional dyspepsia with normal gastric emptying

  • pan-enteric motor disorder

  • diarrhoea predominant irritable bowel syndrome

what is the patient preparation for colonic transit imaging?

not necessary to fast from midnight but many departments do

• cease medications affecting bowel

  • laxatives, opioids, constipation, motility drugs

  • herbal teas causing laxative effects

• every day must check bowel movements with patients, check they are still following medication restrictions

what is the radiopharmaceutical, dose and administration used for colonic transit imaging?

10-15MBq of 67Ga Citrate added to liquid, administered orally

what is the imaging protocol for colonic transit imaging?

• anterior and posterior abdomen FOV

• planar images 6, 24, 48, 72, 96 hours post ingestion

  • start on a Monday

• acquisition parameters 10 minutes, 128x128 matrix

• collimation medium energy

• many places will mark the patient to assist with positioning each day

  • X with a tegaderm

• scan over 5 days, but if no activity left scan can be stopped early

what is the half life of 67 Gallium and what are its gamma energies? (4)

78.2 hours

• gamma energies

  • 93keV 40%

  • 184keV 24%

  • 296keV 22%

  • 388 keV 7%

what is the patient positioning for colonic transit imaging?

keep patient position consistent by marking skin on iliac crests (protect with tegaderm)

usually right ASIS (anterior superior iliac spine) or right lower rib, as long as it is in FOV

make sure there is enough room for whole bowel over the course of the week

what is the image processing and interpretation for colonic transit imaging?

• draw regions of interest over large bowel and bowel segments

  • anterior and posterior projections

  • perform geometric mean calculations

  • correct for radioactive decay of 67Ga

• normal results 97% of activity excreted by 72 hours

• too rapid >>50% activity excreted at 24 hours

  • may also indicate laxatives? check with patient

• constipation >>50% activity remains 96 hours

what are the main structures of the hepatobiliary system? (5)

1. liver

2. gallbladder

3. pancreas

4. small bowel

5. various ducts

what are the main ducts of the hepatobiliary system? (5)

1. left hepatic

2. right hepatic

3. common hepatic

4. common bile

5. cystic duct