VIABILITY STUDY

If you are doing a Thallium study then you take 2 pictures - at 4 hours, and on the next day (24 hours). Obviously, if everything is normal by 4 hours then you don't need to proceed to the 24 hour pictures.

The terminology you use is that

AVASCULAR NECROSIS

This is dead bone from interruption of its vascular supply. This can happen from:
- vessel being damaged (trauma, radiotherapy, vasculitis)
- embolism (lipid, sickle cell)
- venous stasis from compression by osteomyelitis causing increased intraosseous pressure.

I've got no idea why steroids and alcoholism do it.

The nuclear changes come in 4 stages:
1. cold spot because there is no blood supply and therefore no tracer delivery
2. hot spot as new bone is laid down around the edges
3. pain and a hot spot - the pain is because your subchondral bone, which gets its nourishment from the synovium, crumples.
4. the entire femoral head collapses because the repair was not good enough.

The treatment is to replace the dead bone with a bone graft.
If caught early, core decompression to reduce the intraosseous pressure can be tried.

SMALL AND LARGE BOWEL TRANSIT STUDY

This is used for diagnosis of idiopathic constipation.

It is done in two stages:
1. DTPA-saline water is given and images taken until it is seen that tracer has reached the caecum.
Now, before the patient leaves they are given one of the longest-lasting isotopes we have - gallium.

2. Patient goes away but comes back the nexy day, and the next, and the next. If the gallium has still not left the large bowel by then there is something wrong with motility! For example, if it gets stuck in the region of the rectosigmoid region, then this is called "functional rectosigmoid obstruction".


Normal pattern, there is acceptable propagation of activity through colon
without segmental retention of activity during study.

Colonic inertia pattern, there is prominent retention of activity in transverse colon,
Splenic flexure and rectosigmoid region at 48h and 72h.

Functional obstruction pattern, Significant retention of activity seen in the rectosigmoid region.

YTTRIUM SCAN

This is used for bad RA.

The instructions given to the patient are for them to use crutches and a splint until a scan has been done to show that the Yttrium has not escaped the knee and made its way into the lymph nodes or into the soft tissues around hte knee.

So, 3 things to confirm on the 3 images that you will always be presented with:
1. No extravasation outside of knee
2. No hot groin LN's
3. No hot liver

NUCLEAR OESOPHAGEAL STUDIES

1. The transit time for liquid through the oesophagus is 5-11 seconds.

AND

2. There should be <10% of the counts remaining by 15 seconds.

DEMENTIA IMAGING

The imaging agent used is Tc-HMPAO.

The patterns to know are:

ALZHEIMERS - temporoparietal hypoperfusion; posterior cingulate hypoperfusion
- initially asymmetric, becoming symmetric in severe AD


FRONTOTEMPORAL DEMENTIA - frontal, temporal hypoperfusion

VASCULAR DEMENTIA - cortical, subcortical and cerebellar hypoperfusion

LEWY BODY DEMENTIA - occipital and parietal hypoperfusion

PARKINSONS - similar to AD but more occipital changes
- substantia nigra is seen to be absent on dopamine scans

HUNTINGTONS - basal ganglia (caudate & putamen)

ttk: the basal ganglia are in front, right next to the frontal lobes.


Things to know:
1. Anatomy
- the hardest thing to remember is whether the temporal or the parietal lobes are closer to the frontal lobes. Well, it's neither! Both are wedged like a 2-storey structure between the F and O lobes, with the (yellow) P being the 2nd storey.

MIBG SCAN

This is used to diagnose phaeochromocytoma.

The phaeo will be best seen from the back of the patient because the liver and spleen are shining bright from in front.

The things to know so as to understand this scan are:
i) MIBG is made by the body into NA. Therefore it will be seen in tissues that have NA in them - adrenals, heart and NAsopharynx.
ii) It is urinary excreted (which is why you do urinary catechols when looking for a phaeo)- therefore you will see hot bladder and bowel.
iii) It has I in it and so will be taken up by any tissues that are iodine-avid - thyroid, salivary glands, spleen, liver.

Preparations for the scan are critical:
1. If you have iodine in the body then that will be used to make NA in preference to the MIBG. Therefore, no contrast.
2. You don't want the thyroid sucking up all the MIBG. So, give Potassium Iodine for 2/7 before and on the 2 days of image-taking
3. You don't want to stop MIBG being taken up by neuroendocrine tissue. Therefore, don't use:
- cocaine/amphetamines/cough mixtures
- reserpine
- tricyclics
- calcium channel blockers
- labetalol (all the other alpha blockers and beta blockers are OK).