Transcript Alternative Imaging

Alternative Imaging
Chapter 21
Introduction
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Other modalities have assumed
prominence in imaging field, especially
for diagnosis of diseases that are often
difficult to see on radiographs.
Imaging techniques are complementary
to radiography.
Ultrasonography
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Seen in veterinary medicine since the
1980’s.
Can provide information about organ
architecture independent of organ
function.
Helpful in debilitated or young patients
in which contrast agents or exploratory
surgery is contraindicated.
Technical Aspects
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Ultrasound beam is created by a piezoelectric
crystal that oscillates at several million Hertz
per second (mHz) within a tranducer (probe).
When sound wave interacts with tissues of
the body, it is reflected and echo is received
by the tranducer.
Ultrasound machines display images in real
time.
Terminology
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Acoustic impedance- Relationship between
density or stiffness of tissue and the velocity
of sound within the tissue. Differences in
acoustic impedance of adjacent tissues
determine the intensity of the reflected
sound.
Attenuation- Reduced intensity of radiation
caused by absorption or scattering, or both,
during passage through tissue. Sound is also
attenuated as it passes through tissue and
the intensity is reduced.
More Terminology…
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Distant enhancement- Ultrasound artifact.
Increased sound intensity beyond a fluidfilled, anechoic area, created by absence of
attenuation of the sound beam as it passes
through the fluid.
Acoustic Shadowing- Ultrasound artifact.
Echo-free zone created distal to the imaged
organ when sound waves hit a highly
reflective tissue that prevents sound from
being transmitted to greater depths.
And more terminology….
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Echogenicity-Intensity of reflected echoes.
Anechoic- No echoes are detected, and the
area is black. Typically associated with fluidfilled structures such as the urinary bladder.
Hypoechoic- A few echoes are detected, and
the area is low-level gray compared with
adjacent tissues. Usually seen with solid
homogenous tissues or complex fluid
containing cells such as blood.
And one more….
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Hyperechoic- Echoes produced are
brighter than in surrounding tissue.
Clinical Applications
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Echocardiography
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Used to evaluate cardiac disease.
Two modes:
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M-mode (motion mode)- information is displayed as
depth versus time on graph.
B-mode (brightness mode)- Intensity of returning echoes
is expressed as brightness in the display.
No specific preparation, chest wall is clipped, gel
applied and animal is restrained.
Must work between ribs of chest wall.
Difficult in deep chested animals.
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Echocardiography continued.
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Long axis view- Echocardiographic image showing
the heart from base to apex in a longitudinal or
sagittal plane.
Short axis view- Echocardiographic image showing
the heart in transverse plane.
Doppler shift-Difference between transmitted and
received sound frequencies. The greater the
Doppler shift, the greater the flow velocity.
Abdominal Ultrasound
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Patient must be fasted for 12 hours to reduce
the amount of intestinal gas.
Full urinary bladder is optimal for scanning
the bladder or prostate.
Liver and biliary tract:
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Radiographs are superior to ultrasound for
assessing liver volume.
Ultrasound-guided biopsy or fine-needle aspiration
is often performed in conjunction with liver
scanning. (Sedation of anesthesia is required).
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Spleen
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Normal spleen is elliptic, flat, and smoothly
contoured.
Pancreas
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Normal pancreas is narrow, smoothly
marginated and hypoechoic.
Pancreatitis is most common indication for
scanning.
Splenic Mass in a dog
Normal Pancreas of a cat
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GI tract
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Can be difficult due to variable amounts of
gas within the lumen, which reflect sound
and prevent imaging of deeper structurs.
Can be used to identify masses, assess
bowel peristalsis, foreign bodies, and
confirm intussusception.
Intussusception in a dog
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Kidneys
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Normal kidney has hyperechogenic capsule.
Ultrasonography is used when kidneys may not be
visualized on radiographs, or to assess location
and distribution of disease in enlarged kidneys.
Does not assess kidney function unless doppler
technique is applied.
Helpful to identify fluid-filled, cystlike lesions or
solid masses.
Biopsy usually needed to confirm diagnosis.
Lateral Kidney view in a dog
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Adrenal glands
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Normal adrenal glands are small and located in
the perirenal fat medial to the cranial pole of each
kidney.
Left adrenal gland has dumbbell shape while right
adrenal gland is more triangular.
In hyperadrenocorticism, both glands become
enlarged but there is no change in shape.
In cases of masses, usually on one side and alters
the shape of the gland.
Normal Left Adrenal Gland in
Dog
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Prostate
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Normal prostate has homogeneous
echogenicity and fine texture.
Indicated for cases of prostatomegaly,
signs of lower urinary tract disease,
constiplation, and caudal abdominal pain.
Can not differentiate between benign
hyperplasia and neoplasia so biopsy would
be recommended.
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Urinary Bladder
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Normal bladder contains anechogenic
urine.
Bladder is smooth and wall is uniform in
thickness.
Indicated with potential lower urinary tract
disease, stones, masses, etc.
Urethral masses are not visible because are
hidden by pelvis.
Bladder wall tumor in dog
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Reproductive Tract
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Normal reproductive tract in nonpregnant
animals is not normally seen.
Indications are to diagnose pregnancy,
pyometra, stump granuloma, or ovarian
neoplasia.
Pregnancy detection is 30 days after
breeding.
Cervical cancer in a dog.
Early Pregnancy in dog
Late Pregnancy in Dog
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Eyes
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Can place transducer on cornea.
Can visualize components of the eye and
scan for intraocular masses or
hemorrhage.
Extremities
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Focused primarily on equine limb below the
carpus and tarsus.
Computed Tomography (CT)
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One of the most expensive diagnostic tests in
veterinary medicine.
Advantage is can acquire information not
available from radiographs, contrast studies,
or ultrasound examination.
Indications are for central and peripheral
nervous system diseases of the brain, spinal
cord, and lumbosacral spine.
Also useful for obscured masses in the
mediastinum, axillary region, and
retroperitoneal space.
Technical Aspects
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CT uses x-rays and computers to produce images
that show anatomy in cross section.
Allows for visualization of structures in sagittal,
dorsal, transverse, and oblique planes without
superimposition artifact from fat, ribs, spine, pelvis,
or any organs that may mask detail on a survey
radiograph.
Consists of a movable bed or cradle on which patient
lies and a gantry that contains the x-ray tube and
detectors.
Tube and detectors can be moved 360 degrees.
Generally requires general anesthesia.
CT Terminology
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Pixels (picture elements)- Tiny squares
making up the image matrix; represent
voxels.
CT number- Number converted to gray scale
in the final image, which represents the
attenuation of the x-ray beam in tissue within
a voxel. The number is also referred to as a
Hounsfield number, named for the inventor of
CT scanning.
Clinical Applications
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Skull
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Radiographs are generally not extremely
diagnostic of this region.
Lesions can be easily seen by CT.
Indications for skull CT are seizure,
blindness, vestibular signs, and change in
disposition.
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Spine
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CT is helpful with myelography to define
lesions on spine.
Method of choice for imaging spine caudal
to L4-5.
Can allow visualization of intervertebral
disk potrusion.
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Extremities
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Assess coronoid processes in dogs.
Scan both elbows because may be
bilateral.
May also be used to visual meniscal
disease, osteochondrosis, and sequestra.
Thorax
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Indicated with pulmonary and mediastinal
masses, and can evaluate metastasis.
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Abdomen
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Liver, gallbladder, stomach, small
intestines, pancreas, spleen, adrenal
glands, kidneys, ureters, urinary bladder,
prostate, ovary, colon, and major vessels
are easily identified on CT scans.
Useful for canine adrenal masses.
Nuclear Scintigraphy
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Noninvasive imaging procedure that
uses a small amount of radioactive
material administered intravenously,
transcolonically, or by aerosol
insufflation.
Do provide physiologic information
about the function of specific organs.
Technical Aspects
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Radioactive isotope that emits
predominantly gamma rays.
Gamma camera detects the gamma
emissions from the radionuclide and
forms a black and white image of the
selected organ printed on x-ray film.
Terminology
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Labeled Compounds- A compound whose molecule is
tagged with a radionuclide.
Radiopharmaceutical- A radioactive drug that can be
administered for diagnostic or therapeutic purposes.
Half-life (t1/2)- Time in which the initial activity of a
radionuclide is reduced to one half. Biologic half-life
includes exertion, as well as the characteristic halflife of the isotope.
Target organ- The organ intended to be imaged and
expected to receive the greatest concentration of
administered radioactivity.
Clinical Applications
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Thyroid
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Bone
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Evaluates for hyperthyroidism.
Image shows a blackened area in the involved lobe of the
thyroid gland.
Indicated for lameness that cannot be localized by physical
exam.
Liver
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Indicated in patients with a small liver or evidence of a liver
mass, decreased liver function, biliary outflow obstruction,
or abnormal hepatic blood flow.
Looking for portosystemic shunt.