THYROID CANCER ABLATION

After thyroid surgery, use 80mCi if patient has been pre-treated with thyroxine withdrawl, or 100mCi if they have been pre-treated with Thyrogen.

After the ablation dose, they will have a follow-up scan. If this shows remnant disease that you don't think is malignant, give 70mCi. However, if it shows remnant disease that you think is malignant, or there are metastases seen, then give 150mCi.

URINOMA

This shows up as a photopaenic defect.
Delayed images - at 24 hours - will show the previously photopaenic area as full of tracer, because the non-radioactive urine has been mixed with radioactive urine.

It is due to rupture (the renal equivalent of a AAA) of the pelvicalyceal system, usually during a period of strain such as when there is acute obstruction of the ureter, or when there is massive VUR, or from a retrograde pyelogram.

Thus, you get an encapsulated retroperitoneal urine collection sitting in the perinephric space.
Once it gets big enough, it will obstruct drainage from the kidney.

CSF STUDIES

Tc-DTPA or In-111 is used. It has to be injected into the CSF via a lumbar puncture. You can then observe whether:

1. Any appears in the nose = fractured cribriform plate causing CSF rhinorrhea
...an example of a negative study because you see the CSF bathing the brain and spinal cord, but nothing is seen in the nose.

BONE DENSITOMETRY

Osteoporosis is defined as T<-2.5. Osteopaenia is defined as T -1 to -2.5.

i) T score shows your bone density relative to the mean bone density for Thirty year olds of the same sex and ethnicity. A positive number means higher than the mean, and a negative number, lower than the mean.

ii) Z score is the same thing, only for your age compatriots. This is what we use when we evaluate kids for their development. It was these scores that were used when the bone density machines were first invented in the 70’s.

The data for T and Z scores comes from the NHANES study for the hip. However, there is no unifying data for the spine, and so each machine manufacturer uses their own reference range.

The pictures that you use are:

So, what you measure is:

1. The femoral neck, greater trochanter and intertrochanteric region. You then sum these to give you the "total hip" number.

2. The first four lumbar vertebrae.

The reasons why the scan is typically done wrong are:

1. Hip rotation. If the lesser trochanter does not have the same shape then there has been rotation.

2. New spinal pathology that increases the attenuation of the X-ray beam - Paget's, wedge fracture,spinal rods, ...as well as aortic calcification.

So, the first thing to do is to check the images to rule these things out. Then, you check the graph:

You now have an immediate idea of whether their bone density is out of the reference range for them or not.

You confirm this by looking at the next table, which will show the actual bone mineral density, the T score and the Z score.

When you are doing this, there are a few things to be checking off in your mind, to make sure that no technical errors are fudging the results:

1. Are the neck, trochanteric, and intertrochanteric value within a 1/2 standard deviation from the total hip?

2. Are the four vertebrae close to each other in bone density? If not, then this is either a technical problem, or one of those vertebrae has undergone something pathological.

3. On the Lunar company's machines, the Z scores are adjusted for weight. This mucks things up in anorexic and obese people, and is why the Z score can be higher than the T score! (e.g. an anorexic 50yo is compared to other anorexic 50yo's and therefore gets a better Z score than if she were compared to all 50yo's).

The machine calculates the BMD by measuring the BMC (bone mineral concentration) in an Area that the technoloist has drawn lines around. The formula is BMD=BMC/A.

There are some important things to know that stem from this:

- when the spine BMD is reported, the typical value that is mentioned is the L1-L4 BMD. This is not the average of the four BMD's. Rather, this value comes from all four of the BMC's being summed and then being divided by the sum of the four A's. Thus, if one vertebra is no good, a summed lumbar BMD score can still be calculated by using the others.

One other value that is mentioned in reports is the BMAD (Bone Mineral Apparent Density) - this is a volumetirc measurement and is used for short people or kids.

How to report the DEXA:

1. The bone mineral density was done using a Hologic/Lunar/Norland machine.

2. The lumbar spine was X g/cm2 which is X standard deviations below (above) the mean for age-matched persons.
3. The total hip BMD was X g/cm2 which isX standard deviations below (above) expected for her age.
4. The T-score was X at the spine and X at the total hip. This places her in the WHO category of (normal, osteopenia, osteoporosis, established osteoporosis) [NB: need to know about fractures before you can tell the correct category.]...or, for males: The World Health Organization has not specified cut-off ranges for males.

5. Comparison to the previous study...

NB: There are three important things to know about comparisons to the previous studies:-

• Prior to 1997, there was no NHANES data, and so the reference range was quite different and therefore the T and Z scores were created from different reference ranges.
  
• There is a deviation of 2% between results taken at different times on the same machine. A significant difference is therefore only said to be present when there is a 6% difference.
• If the previous bone density was done on a machine from a different manufacturer, then to make a comparison to current bone density, both densities must be converted to standardized units.
  

6. The 10 year probability of fracture is ...

BONE SCAN LIBRARY

Here are the commonest bone scan pathologies you will come accross:

SHIN SPLINTS:
This occurs because the stress on the bone leads to more active osteoclasts clearing the bone so that more can be trowelled on. This trowelling is the periosteal reaction that you see on the scan.
Classic locations are the posteromedial tibia middle-distal 1/3 border. Appearance can be either fusiform or linear.



PAGETS DISEASE:
This will,4 out of 5 times, involve more than one bone. It starts at the ends of long bones and the leading edge of the hot patch has a flame-like appearance.
The bone is bent and thickened.

The differential is damage bone from chronic osteomyelitis, fibrous dysplasia, and osteosarcoma.

OSTEOMYELITIS:
All 3 phases on the bone scan will be hot, unlike in cellulitis, when only the first two will be hot.

GFR STUDY

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).

DMSA

One gives Tc-DMSA and takes pictures 3 hours later. The DMSA is a favourite snack of the PROXIMAL TUBULAR KIDNEY CELLS.

If there is renal failure then the 3 hour pictures will be clouded over by soft tissue contrast, so need to wait another 3 hours.

All that the DMSA will tell you is whether the kidneys are normal size and whether there is any scarring of the cortex.

LYMPHOSCINTOGRAM

This is a very painful test because Tc-colloid is injected in between the foot webspace and one then watches to see how far up the leg it gets.

If it doesn't get to the groin nodes by 2 hours then this is lymphostasis= Milroy's Disease.

It is used to diagnose the cause of non-pitting oedema.

OCTREOTIDE SCAN

This is one of the family of scans that show up the liver, spleen and bladder.
To this family belong:
- MIBG - no bowel seen
- Octreotide - bowel seen
- HMPAO WBC - bowel seen AND marrow seen

Octreotide is bound to either Indium or I-123.
It is taken up by neuroendocrine tumours - carcinoid, medullary ca thyroid, phaeo, euroblastoma, gastrinoma.

It can also be used as treatment therefore if it is labelled with I-131.

PET

n
The reason that you see anything on a PET scan is because the DG in FDG gets into any cell that sucks up sugar, and can't get out of the cell because it is launched down an enzymatic pathway and becomes DG-6-P.
The 18-F that is bound to this then gives off signals.

So, the things that light up are things that use sugar:
- brain
- heart
- strap muscles and salivary glands.
- tongue muscles if the patient is talking
- anything which is very cellular, such as infection and malignancy.

SPINAL BONE SCANS

So, the scans are reported thus:

CHARCOT JOINT IMAGING

A common and difficult situation is where there is the question of infection in a diabetic with a Charcot joint.

The best way to handle this is to go to a WBC scan because the bone scan will be so abnormal that you won't be able to tell whether there is osteoblast activity from trauma or from infection.

Even worse, the late images of the bone scan, which are meant to show only bones, often look like a blood pool image because there is such poor foot perfusion.

CAPTOPRIL RENAL SCAN

This is very simple. You just do nuclear renograms, the first one as per usual, and the second one after you've given Captopril.
If there's a difference in the before and after clearance curves then there's a RAS.

There's a number of medications that need to be stopped before the captopril study:
5 days before - all ACEI and ARB's and all CCB's apart from nifedipine & verapamil
2 days before - nifedipine, verapamil

ATTENUATION CORRECTION

Tissues that get in the way of the photons trying to escape the body cause two types of problems:
1.

DUAL SOURCE CARDIAC CT

The advantages of dual source machines are:
1. Better temporal resolution
2. Reduced radiation dose to the patient because the amount of time that maximal current is given is less.

CARDIAC PET-CT

The major problem is misregistration, which leads to incorrect attenuation correction, typically in the lateral wall.

REPORTING TERMINOLOGY FOR NUCLEAR NEPHROLOGY

The following are useful phrases:

1. There is prompt/sluggish perfusion.
2. There is delayed/normal uptake/excretion(clearance) into pelvis/drainage into bladder (quantify the speed of excretion with the cortical transit time [N<4>400ml/min...based upon this you can say, if the number is less than 400, that "there is bilaterally reduced renal function, more marked on the (side that has the lowest split function number)".

For transplant kidneys, the way you tell function is again by the 2 minute counts. N>4%. You then write "a well perfused and normally functioning transplanted kidney in the RIF with no urinoma".

REPORTING TERMINOLOGY FOR NUCLEAR CARDIOLOGY

The most useful reporting phrase will cover the location and the shade of the cold/hot spot. You then say "resting studies are unchanged/show shade of reversibility/shade less prominent"

Then for any other area you say "with a further area".

The most useful phrase to blow things away is "non-uniformity" or "patchy tracer uptake that is unaltered".

The most useful conclusion will state "findings are most consistent with... but can't exclude..., though this is less likely".
An alternative for a caveat conclusion is:
" test is, at most, mildly positive for ... The defect may also be explainable by attenuation artifact".

OR..."The defect may also be partly explainable by attenuation artifact. Of note, no major area of reversibility is seen".


Useful phrases for reporting:

1. Post stress, there is a small area of mild-moderate hypoperfusion in the distal anterior wall that is less/more prominent at rest. The defect is present on both stress supine and prone images.

2. The exercise MIBI at a low/moderate/high workload did not demonstrate definite evidence of reversible ischaemia. A small amount of reversibility in the distal anterior wall most likely represents breast attentuation. However, in the clinical context of chest tightness, mild distal LAD ischaemia cannot be fully excluded.

3. An accurate LVEF could not be determined.

4. Possible prior moderate-sized infarcts in both the LAD and non-LAD territories.

5. "Patchy perfusion with relative hypoperfusion of the septum and relative hyperperfusion of the lateral wall" means that in the conclusion you will write " Findings are most consistent with a dilated cardiomyopathy".

6. "Relative septal hyperperfusion and relative lateral wall hypoperfusion that is reversible at rest" in the conclusion translates to " the exercise MIBI at a high level of haemodynamic strss does not demonstrate definite reversible ischaemia. Relative lateral wall hypoperfusion is most likely related to exercise induced hypertension".

7. The exercise MIBI study is consistent with a prior non-LAD territory infarct with a moderate amount of ischaemia in the left circumflex and distal LAD territories.

8. If you are not sure whether the findings are ischaemia, cardiomyopathy or a BBB, then write "the findings are explainable by LAD/non-LAD territory ischaemia, but the possibility of a BBB/DCM explaining these findings is significant".

REASONS WHY A NUCLEAR PERFUSION STUDY FAILS

The main one is irregular R-R intervals, because the machine will only capture counts from cycles that fall into a prespecified R-R range. Thus, if you have many cycles which are either too short or too long then the time that the patient is under the camera blows out unsustainably.

IODINE-131 THERAPY FOR THYROID CANCER

The I-131 capsule will only be taken up if the body is hypothyroid. Thus, patients come off the Thyroxine that they were on after their thyroid was chopped out for the cancer.

Unfortunately, apart from the residual thyroid cells, other cells take up the iodine too and this is why the patient suffers:
- salivary and lymph glands === sore mouth and throat
- bone marrow === neutropaenia
- gonads === temporary male infertility
- stomach === nausea, vomiting, abdominal pain

These effects can be minimized by drinking and urinating frequently, and chewing gum.

The iodine is excreted, like all minerals in sweat, and this is why everything that is in the room that you wear and use will be taken away by nuclear medicine staff when the treatment is finished.

It is a hard thing to go through becaue for the first 24 hours there is complete isolation. After that visitors are allowed to come but must stay 2 metres away and not for more than 10 minutes.

NUCLEAR PERFUSION STUDY INTERPRETATION

There are several steps to follow when confronted with a nuclear perfusion study.

1. Go back to the raw data.
The very first thing to do is check the orientation that the technologist has programmed through the ventricle, and reorientate to the long axis of the image if necessary as well as match up the two orientation lines.

2. Now go to the planar data.
You are looking to see:
i) IF LIVER/BOWEL IS MASKING THE HEART (and therefore adding counts to the heart and masking a defect) OR VERY CLOSE TO THE HEART (and therefore stealing counts from the heart and creating a false defect) . IF IT IS THEN YOU HAVE TO RESCAN.
ii) IS THERE A BIG BLACK MASS of breast or pectoral over the heart? IS THE DIAPHRAGM HIGH AND THEREFORE OVER THE INFERIOR WALL?
iii) DOES THE HEART JUMP?
iv) Is there uptake in the lungs (LVF, malignancy) or in the soft tissues?

3. Lastly, you go to the SPECT images.
i) Make sure that the two sets of images have been roughly equally normalized.
ii) Make sure that the count rates are 3:1 on the stress:rest images
iii) Then look for the same artifacts you did on the planar scan - signs of horizontal and vertical motion; spill-over of extra-cardiac counts or counts that are too close for comfort.
iv) Before you go to reading the LV, make sure that the RV looks fine.

When reading the LV, the best way is to follow this system:


So, on first view, what you should be seeing is a donut and two horse-shoes. If you don't then there's something wrong.

Patterns of abnormality:
1. Severe perfusion defect that does not significantly reverse.
The options for this are that either this wall is infarcted or that it is so severely ischaemic that it is not taking up tracer. Such walls are also immobile and so are called "hibernating".
The way to differentiate these two is with a Thallium study.

In terms of the patterns seen, the though process should go as follows:
- If see anterior or anterolateral defect then the first thing to exclude is not ischaemia but breast shadowing. The only way to be absolutely certain is to rescan in the prone position because this spreads the soft tissue out and you do not get as much attenuation.

- If see inferior wall defect, then the first thing to exclude is not ischaemia but diaphragm shadowing. The only way to be certain is to rescan again in the prone position because the heart falls forward and therefore the diaphragm does not cover as much of the heart. However, it creates an anteroseptal artifact because the sternum gets in the way.

If you think that the breast may be responsible for the artifact then rescan prone because this spreads the soft tissue out.

NUCLEAR CARDIOLOGY STRESS TEST

The preparation for the patient is thus:
- no breakfast so that less splanchnic blood flow
- medication restrictions:
3 days - perhexiline, viagra
2 days - BB, nicorandil
1 day - CCB, nitrate

Things that may happen to the patient with the tracer:
-nausea & taste perversion
- techy tinnitus
- allergic reaction
- excreted in the breast milk. It decays such that only 12.5% of the original dose is left after 24 hours.



What this has in common with all exercise tests is the preparation of the skin:
- shave hair
- wipe skin to remove oils
- scrub skin to remove dead cells and thereby increase conductivity

If you are not getting a signal then:
- sticky-tape the electrodes
- move the subclavian leads closer together

What is different from the ordinary stress test is that you always have to wait for 15 minutes afterwards before you image because:
1. In Thallium get diaphragmatic creep
2. In Tc get subdiaphragmatic activity masking the heart. This is also why you give them a glass of something straight after exercise.

MYOCARDIAL PERFUSION TRACERS

Thallium has the advantage of not being taken up by adjacent tissues as much as MIBI. However, it has several disadvantages:

1. When it degrades the photons it gives off have an energy of 73keV and so the pictures are not as clear as the 140keV of Tc.
2. It has a half-life of 73 hours, so the patient receives a large dose of radiation.

The test protocol for Thallium is to stress the patient, take the image and then wait for 4 hours before taking the redistribution image. If all is not normal on this rest/redistribution image then a second dose is injected and reinjection images acquired to see if the defect goes away or if it is a true infarct.

With Tc-MIBI there is a lot of extra-cardiac uptake and so the times that one has to wait after the injection are:- 1/4 hour after a stress & 3/4 hour after a rest, because there is no sympathetic stimulus shutting down the GI system.

CARDIAC CT ARTIFACTS

Beam hardening artifact is when get streaks accross the image from something dense.

RADIATION DOSES

The natural yearly dose from just living is 3mSv. This is the same as having one bone scan.

One MIBI scan gives at least 4mSv.
One mammogram, 1mSV.
One CXR, 1/100th of a mSV, this being the same dose you get for every 1000 miles you fly.
One CT chest or abdomen 7mSV.
One CTA gives up to 15mSV.
One Thallium gives 20mSV.

whereas, one Urea Breath Test only gives 3 MICRO Sv (i.e.1/3rd of a CXR).

CARDIAC CT

Most machines have one X-ray tube that shoots out X-rays but multiple detector plates that pick up the X-rays that have come through the patient.
So, it doesn't take long for a region of the patient to be caught on film because that region is quickly moved past the X-ray tube and detection plates by the moving table.

As the region moves past, the X-ray tube varies its output so that maximum tube current and therefore radiation is only given during diastole. This significantly reduces the total radiation dose to the patient. Why diastole? - because the heart is not moving as much and so images are crisper. Why not give no dose during systole then? Because paradoxically sometimes the systolic phase - at 35% of the RR interval - gives the crispest image (so you don't want to lose that window of opportunity)!

Before the patient even gets to the machine a few thing happen:
- they abstain from food for 3 hours but keep on drinking because dehydration leads to tachycardia
- they abstain from coffee for 24 hours so that the heart rate is not fast
- they abstain from viagra, etc., for 24 hours because GTN will be given once they are lying on the scanner to maximize the size of the coronaries. You use a full size GTN for everybody unless they weigh 55 kilos or less (a nice number to remember!), also because the dose of the metroprolol is 5mg :)
- they get beta-blocked with IV metroprolol to a HR of <65bpm. The dose used is 2.5-5mg and one doesn't go beyond a dose of 40mg.
- if they have a pacemaker then it is set to a HR of 60bpm and beta-blockade is then given until they reach 60bpm.

There are actually several shots taken by the machine, not just the coronary shot.
The first is a "scout" shot - it looks just like a plain film CXR.
On this scout one then draws a box to tell the machine to only detect X-rays in this box. The box typically begins a little above the heart, and ends a little below the diaphragm, with the side margins of it covering the lung fields all the way out to the chest wall.

A very small blob of Iodine fluid is then injected into an peripheral IV and one measures how long the iodine takes to reach the aorta. This will tell you how long to tell the machine to wait after the injection before it starts to shoot out X-rays (else will get unnecesary radiation).

Then, the real deal.

Things to know:
1. Because the dose of iodine is so small, it is very concentrated (360mg/ml) and shot into the veins very fast - 5ml/sec (that number 5 again!). Typical doses are 75ml or 100ml if CAGS.
2. If you want to evaluate the right heart too then you give a second bolus of contrast - 25ml at 2.5ml/sec.
3. The machine is typically scanning for 10-15 seconds.
4. Slices are no thinner than 2/3rds of a MILLImetre. That means that 1/3 of each MILLImetre is not captured. The reconstruction that is first tried is at 70-80% of the RR interval. However, for the low current part of the scan, the reconstruction lumps 2mm worth of data together and then ignores the next 2mm of data.
5. If the heart rate cannot be brought down then no dose modulation is given because you may need the systolic frames. Thus, the dose to the patient is twice as high.

PHARMACOLOGICAL STRESS TESTS

You can use either adenosine, dobutamine, persantin or an adenosine receptor agonist.

The adenosine receptor agonists that are around are all called "-denoson's".
They all stimulate the 2A subtype of the adenosine receptor, this being the one that is responsible for the coronary vassodilation. It's easy to remember that it's 2A because the drug class is A2A and so there are 2 A's :)

In terms of the other subtypes:
1 commands the AV node
2B is responsible for bronchoconstriction
3 for histamine release

The big study that compared side-effects to Adenosine was ADVANCE MPI (because these drugs were thought to be an "advance". It showed that heart block was not caused and that there was less chest pain, SOB and flushing, but more headache and GI upset.

With regards to Persantin, the dose given is 140mcg per kg per minute for 5 mins. So, this is 600mcg per kg.

You don’t give it if:
- CHB on ECG
- Recent hospitalization for asthma
- Wheezing on chest auscultation

LACRIMAL DRAINAGE STUDY

A drop of Pertechnetate is dropped in each eye and images taken over the next 20 minutes.

If the scan is normal then it looks like the two lines from the eyes touch in the midline of the face, below eye level.

SENTINEL NODE SCAN

Essentially you inject Tc-labelled nanocolloid into where the cancer is and wait for a 1/2 hour to see where hot spots appear. Usually there will be several.

Each of these hot spots that appear is a node and you then mark the skin at those sites so that the surgeon can cut where X marks the spot (to biopsy those nodes).

PARATHYROID SCAN

This uses Tc-MIBI. So, it's not surprising that you see uptake in the heart and liver.
However, MIBI also goes to the thyroid and parathyroid.

The ability of the scan to diagnose parathyroid adenomas rests on the fact that these are rich in mitochondria.

So, after 1.5 hours of imaging, any spots that are still hot are going to be mitochondria-rich tissues. This could be a parathyroid adenoma, a carcinoma or for that matter a thyroid adenoma or carcinoma.

This is why the next step is to take a SPECT and see whether the hot point is lying where the thyroid lies or where the parathyroid lies.

NORMAL PAEDIATRIC BONE SCAN

All that you have to know is that the growth plates are located at the ends ("epiphyses") of long bones and are the most active parts of the skeleton. So, they always look hot.

So, it looks like the child has:
- 2 anklets and 2 watches
- a stripe on either side of the knee and elbow
- an ipod on both shoulders
AND FINALLY
- a stripe in both groins

So that makes 4 stripes in the arm, 1 in the groin and 3 in the leg = 8 stripes to account for on either side.

HIDA SCAN

The body can't tell the difference between HIDA and bilirubin. So, if you give Tc-labelled HIDA then you will get a map of the entire biliary tree within 1/2 an hour.

If you don't see the gallbladder then it means the cystic duct is blocked (i.e. acute cholecystitis).

If you don't see the bowel then it means the CHD or CBD is blocked. How do you know which it is? Simple - if you see only tracer in the liver and the squiggly lines over the liver then it never got to the CBD, which is the straight line heading downwards at 6 o'clock just outside the liver.

NB: The way the liver bit is reported is that if you see the liver looking like a liver then you simply say "normal liver uptake".

LABELLED RED BLOOD CELL SCAN

This scan is a MUGA scan except that the camera focuses on the abdomen and not the heart. So, stannous follows by technetium is used.

You will see the blood vessels, the liver and the spleen in the picture ass well as the bladder because not all the technetium gets bound - some gets excreted into the bladder. You should not see anything else in the abdomen - if you do then that's the leak of blood into the bowel.

MECKEL'S SCAN

Pertechnetate is injected. You should just see it in glands - therefore, salivary, thyroid and stomach.

If a Meckel's is there, it will also be seen. It is usually at the bottom of the picture, to the side of or behind the bladder.

LABELLED WHITE BLOOD CELL SCANS and GALLIUM

There are three types:

1. WBC's labelled with Tc and HMPAO. This is preferred because the dose to the patient is 3mSv.

The way this is done is to take whole blood, spin it down, take off the white blood cells and baste them with Tc HMPAO. This takes 3 hours to do!

You will normally just see hot liver and spleen and faintly hot marrow, because this is where white cells hang out in the body. Images are typically taken once an hour, so the patient is sitting around the department for another 3 hours!
This is a problem if you are trying to see if there is a splenic or hepatic abscess. Then you need to look for cold spots.

However, after 3 hours of imaging, the actual Tc-HMPAO (not the white blood cells) is pooed out and so you see hot bowel.

You try to minimize this as a problem by having the patient fast the day before and take Golytely the night before. This means that there is no poo for the HMPAO to tack on to.

A classic situation to be aware of is when you have a bone scan that is hot but a white cell scan is cold. In this case, the likely situation is treated cellulitis. The differential is treated osteomyelitis. You can differentite the two by how hot the bone is. If it's hot, then it was OM because bone images take weeks to improve. Whereas, if it was cellulitis, then the bone will only be warm, and that's because the cellulitis will have led to increase blood flow to the entire area, and so more MDP will have been available to be taken up by the bone - therefore that bone will appear hotter.

2. Indium-labelled white blood cells. This is used for abdominal imaging because Indium is not pooed out.
The drawback is that you get 3x the radiation dose (3 x 3mSv is the mnemonic).

3. Leukoscan, which is a monoclonal antibody that is removed from protesting mice, having been developed in those mice by injecting them with human WBC's.

The alternative is GALLIUM.
The advantage is mainly for patients who might have an infected prosthesis. This is because the prosthesis will squish marrow and therefore you will have a hot WBC scan around the prosthesis. Therefore, you need to do a sulfur colloid marrow study to see if there is a similar appearance of hotness.
Whereas, gallium will not be hot unless there is an infection.
The disadvantage is that it gives a high radiation dose and one needs to wait several days after giving it before you can take pictures (and therefore are unsure for those days whether you have an infection or not)

BONE SCAN OF THE HANDS and FEET

The mnemonic to remember the hand bones is:
"some lovers try positions that they can't handle"
&
"trapezium to the thumb"

proximal row: scaphoid, lunate, triquetrum, pisiform
distal row: trapezium, trapezoid, capitate, hamate

In the first four days after a fracture, a bone scan can be negative. This is because it takes that long for enough osteoblasts to show up on a scan, to become activated.



The mnemonic to remember the foot bones is:
3 cuneiforms make up the medial foot distal row
cuboid the lateral foot distal and middle row
navicular the medial foot (big toe side) middle row
calcaneus the lateral side of the proximal row and talus the medial side of the proximal row.

So,

cccC
(a)N(d)
CT

...or the navicular/boat sails on the C's.

Here are some classic images.
Talonavicular joint arthritis:



2. If have all of the carpal bones hot then think of an INFLAMMATORY ARTHRITIS, one type of which is GONOCOCCAL. Therefore, do a whole body scan.
Other things to know are:
Low frequency gives fuzzy objects an a fuzzy background.
High frequency filters give crisp images with a lot of noise