Nuclear Scintigraphy, CT and MRI

Nuclear Scintigraphy

 an imaging modality that utilizes a gamma camera to track radioactive uptake in structures or organs of interest

Atomic Number

Number of protons in a nucleus

Atomic Mass

Sum of the protons and the neutrons in a nucleus

Radioactive

 Meaning that the atom is emitting ionizing radiation or particles

Isotope

 Same element, but contains a different number of neutrons

Half-Life

The time taken for the radioactivity of a specified isotope to fall to half its original value

Radiopharmacy

• Atomic number: Number of protons in a nucleus

• Atomic Mass: Sum of the protons and the neutrons in a nucleus

• Radioactive: Meaning that the atom is emitting ionizing radiation or particles

• Isotope: Same element, but contains a different number of neutrons

• Half-life: The time taken for the radioactivity of a specified isotope to fall to half its original value

Atomic Structure

• Proton +

• Neutron: no charge

• Electron -

• Nucleus: Made up of positively charged protons and neutrons that contain no charge

Radioactive decay

• Disruptions of the atom

  • Nucleus beings to shake

• Release of different forms of energy

  • Alpha emission

  • Beta emission

  • Gamm radiation

Alpha emission

loss of 2 neutrons and 2 protons

Beta emission

 loss of 1 electron

Gamma Radiation

Pure wave of immense photon energy

• Have the shortest wavelength and contain the most energy of any wave on the electromagnetic spectrum

  • In space, these rays are created by events such as supernovas and black holes

  • On earth they are created by radioactive decay

Technetium 99m

• Most widely used radioisotope in nuclear medicine

  • Emits gamma radiation

  • Short half-life - 6 hours

MDP

• Methylene Diphosphonate

  • Tracer

  • Seeks out areas of high osseous turnover

Making Technetium 99m

1. Molybdenum is placed within a generator

2. The atom is disrupted

3. It begins to decay

4. Once it decays into Tc 99 it can be eluted and drawn into a syringe

5. The syringe is then ready to be injected into the patient

• This is a very time sensitive process because the isotope will continue to decay over time. It must be properly calibrated to the time that the isotope will be injected into the patient

Various types of nuclear scans

MAIN ONES

• Equine Bone scan

• Cat Thyroid scan

Day PRIOR to equine bone scan

• Request received

• Isotope dose is calculated and ordered to be calibrated in coordination with injection time

• Prep camera with colbalt flood

  • The horse is what is radioactive not any of the imaging equipment

• Box is prepared to be taken to stall - leg wraps, foot wrap, radiation signs etc.

Day OF Equine bone scan

• Isotope processed

• Camera peaked to the isotope

• Horses legs/feet wrapped

• Catheter placed - horse injected

• Wait 2 hours

• Give sedation - walk to nuclear room

• Put on blocks - start at feet and move up

• Bathroom break for horse

• Scan caudal half of horse

• Horse geigered - hand held tool to check the radiation amount they are reading at

• Room surveyed for contamination

Day AFTER equine bone scan

• Horse will be geigered again

• If it is under 120 mR/hr it will be released to go home or have further work up/diagnostics

• Horse moved to new stall

TWO DAYS after equine bone scan

• Stall is geigered

• Must read background (0.02 mR/hr)

• Signs removed from stall

• Trash removed from stall

• REM contacted for trash pick up

3 phases of nuclear imaging

1. Vascular phase

2. Soft tissue Phase

3. Bone Phase

Vascular phase

• Image is acquired simultaneously with injection of the isotope

• Traces the isotope as it moved through the circulatory system

• Indications for use

  • Suspect thrombosis

  • Decreased perfusion

• Not commonly performed

Soft tissue phase

• Image is acquired 5 minutes post injection of isotope

• Detects soft tissue inflammation

  • Trauma - ex. Kicked by another horse

  • Saddle soreness

  • Muscle injury

• Used more commonly than the vascular phase

Bone Phase

• Scan begins 2-4 hours post injection of isotope

• Technetium 99m - MDP seek areas of High osseous turnover

  • Bone injuries - stress fractures

  • Osteoarthritis

  • Neoplasia

To obtain good nuclear images

• Requires 2-3 staff members

• The horse must remain completely still - typically very sedated

• When imaging the distal limb, lead shielding is placed between the legs

• Camera face is positioned around the horse

• Effectiveness of lead shielding for personnel remains controversial

  • At Purdue we do not have to where lead shielding

• Whole body scan average: 3-4 hours

• Half body scans average: 1-2 hours

Time length for whole body nuclear scan

3-4 hours

Time length for half body nuclear scan

1-2 hours

How the equine nuclear image is obtained

1. Isotope emits gamma rays from area of uptake

2. Rays pass through the collimator on camera

3. Rays interact with sodium iodide crystals within camera

4. Reaction causes rays to be scintillated into photon light energy

5. Photomultiplier tube converts the light waves into electrical pulses

6. If the pulses fall within the photo peak window they are transcribed into a digital image

How nuclear images are interpreted

• Areas of high uptake will appear bright red or "hot"

• Areas of low uptake will appear blue or "cold"

• Uptake does not directly relate to pain!

Nuclear image - Red areas

• Area of HIGH uptake

  • Signs of active skeletal growth

  • Especially useful in localizing bone injuries

Nuclear image - Blue areas

• Areas of LOW uptake

  • Can represent a normal region or an area lacking perfusion

  • If entire distal limb is blue you probably have a perfusion issue

Information Nuclear scans provide

• Nuclear scans are sensitive but not specific

  • Ex. Could potentially pick up on a stress fracture that would not be able to be seen on radiographs

  • However, cannot tell you that the problem is a stress fracture

• Nuclear scans act as a diagnostic compass

  • They localize of problem, but don't provide a diagnosis

What happens after a nuclear scan

• Nuclear scans must be used in conjunction with other diagnostics

  1. Reassess the lameness

  2. Take radiographs of localized area

  3. Potential Cross sectional imaging

     1. CT is much more specific

  4. Ultrasound if useful

Cat Thyroid Scan

• Performed if there is suspicion that the cat is hyperthyroid

  • Isotope: Sodium Pertechnetate

  • Cat injected - wait 20 minutes

  • 5 scans - ventral, dorsal, both laterals and pinhole

  • Looking for uneven distribution of uptake in the thyroid

Isotope for Cat thyroid scan

Sodium Pertechnetate

ADVANTAGES of Nuclear imaging

• Ability to scan the entire body

• Provides valuable information about soft tissue, bone and vasculature

• Does no require general anesthesia (for horses)

• Provides valuable information in the diagnostic process

DISADVANTAGES of Nuclear imaging

• Not specific enough for diagnosis

• Uptake does not necessarily mean the source of lameness

• Time consuming

• Effectiveness of PPE is controversial

• Patient remains radioactive post scanning

Summary of Nuclear Scintigraphy

• Good diagnostic tool in terms of localization

  • Diagnostic compass

• Must be used in conjunction with other diagnostics

• Relatively low radiation exposure to patient

• Detection of bone abnormalities

• Does not always uncover the source of lameness