Radiology Grad Class Flashcards
What is the difference between a pixel and a voxel?
A pixel is a 2D structure; a voxel incorporates a third dimension (the slice thickness of that tissue).
What is the approximate window level for air?
-1000
What is the approximate window level for fat?
-100
What is the approximate window level for soft tissue [brain]?
+30-40
What is the approximate window level for bone?
500-1000
What is pitch?
The distance of table movement per rotation
What does changing the pitch from 1 to >1 do to image quality? What about
1 - normal
>1 - worse quality (gaps)
What is the relationship between photoelectric effect and atomic number?
PE effect is related to the cube of the atomic number
What are three contraindications for IV use of an iodinated contrast agent?
Dehydration/hypovolemia
Renal failure (ARF or CRF)
Disruption of BBB
In very general terms, what do T1 and T2 refer to regarding electron behavior?
T1 is how long the electrons take to come back up. T2 is related to their spin.
What is the safest position if performing a negative contrast (air) cystogram? Why?
Left lateral recumbency. If air embolizes it will get trapped in uppermost part of right ventricle and is less likely to go to lungs.
What is the normal diameter (relative to another anatomic structure) of the small intestine in dogs? Cats?
What is definitive for ileus in dog?
Dogs - no more than 2x width of rib
Cats - no more than 2x height of central L4
Dog ileus - 4x width of rib
What is the barium dose for a GI series?
5-6 ml/lb
On the “mushroom” view on echo, what is normal L ventricle size relative to R ventricle?
L should be 3x the size of R
What is normal fractional shortening for
- small breed dogs?
- large breed dogs?
- cats?
small breed: 35-45%
large breed: >25%
cat: 45-55%
What is the normal ratio of aorta to left atrium in dogs?
1 : 1.3
What is the normal left atrium diameter in cats?
less than or equal to 1.5 cm
What is the limitation of pulsed-wave doppler for echocardiogram?
It can’t measure high velocities
What is the normal thickness for septum and left ventric free wall in systole for cats?
less than or equal to 0.6 cm
On echo, what is the diagnostic view for diagnosis of PDA?
RVOT
What is particulate radiation?
Beta articles/electrons
What is electromagnetic radiation?
X rays and gamma rays
What is the definition of a Gy?
100 J/kg
Give 3 examples of teletherapy?
Orthovoltage, Cobalt, Linac
Give 2 examples of brachytherapy?
Strontium 90, Iridium 192
Give 2 examples of internal radiation
I-131, Samarium-153
What predominates at higher energy - Compton effect or photoelectric effect?
Compton
What is the difference between lymphocytes and other cells regarding response to radiation therapy?
Lymphocytes experience immediate interphase cell death; other cells have to proceed to mitosis.
What is the law of Bergonie and Tribondeau?
radiosensitivity is directly related to mitotic activity and inversely related to cell differentiation.
By what factor are well-oxygenated cells more sensitive to radiation therapy?
2.5 to 3 times more sensitive when well oxygenated
In what phase of the cell cycle are cells most sensitive to RT?
G2-S transition
What percentage of congenital shunts are extrahepatic? What is typical signalment?
60% of congenital shunts, tend to be small breeds
What percentage of congenital shunts are intrahepatic? What is typical signalment?
35% of congenital shunts, tend to be large breeds
What percentage of shunts are acquired?
20%
How is shunt fraction used in scintigraphy for diagnosis of shunts?
ROIs are liver and heart
20% is shunt
What are the four categories of shunts that are differentiated on scintigraphy, and how do they appear?
Splenocaval - looks like a curlie-cue
Azygous - dumps in front of heart
Portocaval - dumps into caudal aspect of heart
Acquired - stays in spleen longer [portal hypertension], then runs caudal and ventral
What is the ultrasonographic appearance of the kidney relative to the liver and spleen?
hypo to spleen
iso to liver
What is normal renal length in cats?
3 - 4.3 cm
Give 5 differentials for increased renal cortical echogenicity in cats.
FIP Lymphoma nephritis metastatic SCC fat
What causes medullary rim sign?
Mineralization of the basement membrane at the corticomedullary junction.
Name the 4 layers of the bladder and their appearance on ultrasound
mucosa - hypo
submucosa - hyper
muscularis - hypo
serosa - hyper
How long after breeding can fetal heartbeats be seen on ultrasound?
25 days
What are signs of fetal death on ultrasound? Give 4.
lack of fetal heartbeat
excessive fluid
excessive gas
lack of expected detail
What is standard wall thickness of GB in dogs and cats?
Dogs: 2-3 mm
Cats: 1 mm
On ultrasound, what causes clean and dirty shadows?
Clean - Mineral
Dirty - gas
What is normal spleen thickness on ultrasound for cats?
1.5 cm)
What are three characteristics of splenic nodules that would suggest neoplasia?
Complex echotexture
Distortion of capsule
Reactive mesentery
What are the layers of the GI tract wall as they appear on ultrasound?
lumen-mucosa interface: inner white
mucosa: black (thick)
submucosa: white
muscularis: black
serosa: white
What is upper limit of normal for SI wall thickness in dogs? Cats?
dogs: 5 mm
cats: 2.1 mm
What is normal diameter of common bile duct?
no more than 2-4 mm
Describe the Salter-Harris fracture patterns
I - fracture along physis
II - fracture along physis into metaphysis
III - fracture along physis into epiphysis
IV - fracture from epiphysis into metaphysis (crosses physis)
V - crush fracture along physis
Mneumonic: S A L TE R Slip Above Lower Through everything Rammed
What is the Larmor frequency?
The radiofrequency transmitted into the patient during MRI; strength is related to the strength of the magnet.
What is TR in relation to MRI?
Repetition time - the time between one RF pulse and the next.
What is TE in relation to MRI?
Echo time - the time from the RF pulse until the machine records the signal.
What are TR and TE in a T1-weighted image?
Short TR and short TE
What are TR and TE in a T2-weighted image?
long TR and long TE
What are TR and TE in a proton density weighted image?
long TR and short TE
In general, what does a lesion’s presence do to:
- T1 relaxation time
- T2 relaxation time
- number of protons
It increases all of them
What is the appearance of fat on T1 and T2?
bright on T1
moderate on T2
What is the appearance of fluid on T1 and T2?
dark on T1
bright on T2
What is FLAIR good for?
It is a T2 weighted image that suppresses CSF, highlighting adjacent lesions
What is STIR good for?
It is a T2 weighted image that suppresses fat
