cross sectional imagingpathology

8/12/2019 Cross Sectional ImagingPathology

1/51


2/51

www.upei.ca/~vetrad

Computed Tomography

(CT)


3/51

www.upei.ca/~vetrad

Cross Sectional Imaging

No superimposition of structures

Excellent contrast resolutioncan see

the difference between 2 similar tissues For CTscan can be performed in one

plane (usually transverse) and

reformatted in the others (sag, dorsal) CTgood for bone and soft tissue

MRIbetter for soft tissue


4/51

www.upei.ca/~vetrad

Computed Tomography

Uses X-rays, X-ray tube, detectors,

collimatorsvery similar to radiography

in how it works. Patient placed in gantry

Multiple samples are taken from around

the patient and then reconstruction canoccur to make a slice


5/51

www.upei.ca/~vetrad

CT Generations

Generation configuration detectors beam min scan time

First translate-rotate 1~2 pencil thin 2.5 min

Second translate-rotate 3~52 narrow fan 10 sec

Third Rotate-rotate 256~1000 wide fan 0.5 sec

Fourth Rotate-fixed 600~4800 wide fan 1 sec

Fifth electron beam 1284 detectors wide fan electron beam 33 ms

Helical and Multislice CTs are used now


6/51

www.upei.ca/~vetrad

How It Works

Scout image is made first to pick the

area to scan

Parameters set on the computer

Scan begins

Linear attenuation coefficient of tissues

Houndsfield units calculated

Shade of grey assigned to a CT number


7/51

www.upei.ca/~vetrad

CT Principles

The image is divided into small areas

called pixels

Each pixel has a location

Each pixel has an attenuation value

Using this information and very complex

math formulas, the computer constructsthe image


8/51

www.upei.ca/~vetrad

CT numbers

High CT number = white because ofincreased attenuation

Low CT number = black because ofdecreased attenuation

Houndsfield scale

Water is zero, air is

1,000 and bone is1,000

256 shades of grey


9/51

www.upei.ca/~vetrad

Windowing

Level

Center portion of the Houndsfield scale

that is being used Should be near the tissue of interest

Width

How much of the Houndsfield scale is used Values within the window will be various

shades of grey - rest black or white


10/51

www.upei.ca/~vetrad

Level and Width


11/51

www.upei.ca/~vetrad

Windowing - Use Narrow windowenhance contrast of the

tissues

Brain

Wide windowarea with high inherentcontrast

Lungs

Soft tissue window

Bone window

Reformattingcan not be better than original

slicedecreased spatial resolution


12/51

www.upei.ca/~vetrad

CT Terminology

Density

Hypodense

Isodense

Hyperdense

IV Contrast can also be administered

then contrast enhancing, ringenhancement etc can be used


13/51

www.upei.ca/~vetrad

Soft Tissue Bone


14/51

www.upei.ca/~vetrad

Choroid Plexus Tumor


15/51

www.upei.ca/~vetrad

Fibrosarcoma Cat Back


16/51

www.upei.ca/~vetrad

Multilobular

Osteochondrosarcoma


17/51

www.upei.ca/~vetrad

CT images


18/51

www.upei.ca/~vetrad

Bone Lysis Nasal Tumor


19/51

www.upei.ca/~vetrad

Nasal Adenocarcinoma


20/51

www.upei.ca/~vetrad

Retrobulbar Mass


21/51

www.upei.ca/~vetrad

Pituitary Tumor


22/51


23/51

www.upei.ca/~vetrad

Magnetic Resonance Imaging

Does not involve ionizing radiation

Uses magnetic field and radiofrequency

pulses

Hydrogen proton on tissues (water)

Water = like tiny magnets

When placed into magnetic field H

protons line up along field


24/51

www.upei.ca/~vetrad

MRI

Radiofrequency pulse passed through

patient

Protons flip and spin

Pulse turned off and H protons return to

normal state = relaxation

T1

T2


25/51

www.upei.ca/~vetrad


26/51

www.upei.ca/~vetrad


27/51

www.upei.ca/~vetrad

Meningioma Hydrocephalus


28/51

www.upei.ca/~vetrad

MRI

Tissues that have little H protons havelittle signal and are black

Air, bone, moving blood Good for soft tissue imaging though

Paramagnetic contrast agentGad

No reformatmust scan all planes Thus much longer scan than CT

Transverse, sagittal, dorsal


29/51

www.upei.ca/~vetrad

T1 vs. T2


30/51

www.upei.ca/~vetrad

MRI Machines

Can vary from .3 Tesla to 3 Tesla for

routine working machines

Many are superconductinguse helium

Magnet is always on and must be

contained in a Faraday cage (blocks

stray radiofrequency signals) Open and closed magnets


31/51

www.upei.ca/~vetrad

MRI Terminology

Intensity

Hyperintense

Isointense

Hypointense

Contrast enhancing with Gadolinium


32/51

www.upei.ca/~vetrad

MRI Safety Augment T waves on EKG

Light flashesMild skin tingling

Involuntary muscle twitching

Increased body temperature

Projectile effects

Effects on surgical implantsferrous

Magnetic foreign bodies

Life support devices


33/51

www.upei.ca/~vetrad

MRI Contraindications

Pacemaker

Intra-cranial implants, clips

Metallic foreign bodies

Implanted electrical pumps, mechanical

devices


34/51

www.upei.ca/~vetrad

Nuclear Scintigraphy

(Nuc Med)


35/51

www.upei.ca/~vetrad

The Basics

Radionuclides (radioisotopes) are used Injected, oral, per rectal etc. administration

They undergo decay over time

Linked to a radiopharmaceutical Determines the area of distribution

Gamma rays come from the patient Radioactiveionizing radiation is involved

Gamma camera detects the radiation

Good for physiologic function stuff

Does not provide a good anatomical info


36/51

www.upei.ca/~vetrad

The Ideal Radionuclide

Technetium 99m

Short half life = 6 hours

Binds to radiopharmaceuticals

Cheap to purchase


37/51

www.upei.ca/~vetrad

The Gamma Camera

The gamma rays produce scintillations

They are converted to electrical signals

and multiplied by photomultiplier tubes

The computer records the strength and

location of the scintillation events


38/51

www.upei.ca/~vetrad

Types of Scanning

Static

Images are acquired os structures at a single point

in time

Dynamic

Images are acquired of a structure over a period

of time

Provides functional activity

Time activity curves

Activity in a region is followed over time and a graph made


39/51

www.upei.ca/~vetrad

Bone Scans

One of the most common scans we do

Equine

3 phases:

Vascular phase

Soft tissue phase

Bone phase


40/51

www.upei.ca/~vetrad

Items to Consider

Age of the animal

Young animalsphysis

Older animal

longer time to distribution ofradiopharmaceutical

Must scan both limbs etc even if only one is

suspected of being abnormal

Symmetry is your friend

Animals are radioactive for a time after the

scan


41/51

www.upei.ca/~vetrad

Normal Equine Bone Scan


42/51

www.upei.ca/~vetrad

Bone Scans


43/51

www.upei.ca/~vetrad

Equine Head


44/51

www.upei.ca/~vetrad

Thyroid Scintigraphy

Technetium99m Pertechnetate

Uptake in thyroid glands is compared to

uptake in salivary glandsshould beequal

HyperthyroidBenign adenoma

Thyroid glands exceed salivary glands

Functional thyroid tumors

Patchy irregular inconsistent pattern


45/51

www.upei.ca/~vetrad

Thyroid Scintigraphy Scans


46/51

www.upei.ca/~vetrad

Portosystemic Shunts

Technetium 99m is placed in the rectumand dynamic images every 4 seconds

are acquired over 2-3 minutes Non invasive, quick, accurate,

quantitative

Liver then heart = normal

Heart then liver = abnormal (shunt)

Time Activity Curves - important


47/51

www.upei.ca/~vetrad

0

200

400

600

800

1000

0 20 40 60

Heart

Heart

Liver

Time Activity CurvePortosystemic Shunt


48/51

www.upei.ca/~vetrad

Shunt vs. No Shunt


49/51

www.upei.ca/~vetrad

Other Scan Types

Renal Scans To determine GFR and ERPF

Cardiac Scans

Hepatobiliary Scans Hepatocyte function, function of the

reticuloendothelial system, biliary function

Gastrointestinal scans

Lung Scans

Infection and tumor imaging


50/51

www.upei.ca/~vetrad

Nuc Med Safety

Higher energy radiation

Especially before injection

Urine from horses Bedding

Isolation

Lead for workers

not work

Wear plastic gloves to keep off hands

Wear monitoring badges, rings


51/51

www upei ca/~vetrad

Release Protocol

Isolation of the animals is necessary

Limited contact with the animal

Very sick animals may not be best to inject

Bedding must be monitored

Animal must be released after scanning

with Geiger counter

cross sectional imagingpathology

Documents