Famous Study Guide - General Flashcards
How many CCs of contrast per Kilogram of pt weight in an adult?
1-2 cc/kg
What is the 1st drug administered for anaphylactic shock?
epinephrine
What is the first drug administered for a vasovagal reaction?
atropine. Heart and BP drop and atropine speeds up the heart rate
What anatomical region is imaged if a glioma is suspected?
Or … Astocytoma, Schwan Cellanoma, oligodendroglioma
Brain
What are the types of detectors commonly used in CT systems?
Scintillation (solid state) & Gas (Xenon)
What is the advantage of scintillation detectors over xenon gas?
More efficient
What determines pixel size?
DFOV (SFOV) divided by Matrix size
What is quantum noise related to?
Number of detected photons (could reduce quantum noise by upping the mAs)
How can a ring artifact be corrected?
recalibrate the detector or detector gain
What determines the Voxel volume?
Voxel volume = Pixel Area X Section Thickness
Pixel area = FOV/Matrix X FOV/matrix (answer in mm2)
(field of view divided by matrix times field of view divided by matrix)
Pixel area in mm2 times section thickness in mm (answer in mm3)
What information set must you have to change the DFOV (displayed field of view) after a
scan has been completed?
Raw Data aka Scan Data
What is the normal adult creatinine range?
0.6 - 1.2 mg/dl
What type of Contrast Media is utilized for a biopsy of the pancreas?
Oral Water Soluble Iodinated
NO barium for any biopsies
What type of archival system is NOT used to store LONG term data?
Hard Drive (Disk)
What type of artifact is caused by a metal prosthesis?
Streak (beam hardening artifact)
What does spatial resolution depend on?
Algorithm (Reconstruction), and voxel size
Voxel size is related to … Pixel Size and Slice Thickness,
Pixel size is related to … Matrix Size, Displayed or Scanned FOV
So… spatial resolution is related to algorithm, FOV. Matrix, thickness
The Seminal Vesicles are located?
posterior to the bladder, anterior to the rectum, superior
to the prostate gland
Why would a soft tissue algorithm be selected?
Or… What does a soft tissue algorithm do?
Increases contrast resolution,
But most of all decreases noise
What effect does a bone algorithm have on a CT image?
Increased image noise
What causes a streak artifact generally found between the fundus and
body of the stomach?
Air-Contrast interface or edge gradient
What artifact is commonly found between the petrous ridges and brain
tissue and is caused by x-ray penetrating bone and traveling over soft tissue?
Beam Hardening or cupping
What is partial volume averaging?
Two or more tissue types contained in one pixel can
give ROI reading of (average) pixel values (wrong CT numbers)
Answer: Several (generally) small anatomic structures, contained
within a voxel – averaged together and therefore become
indistinguishable from one another
Answer Results in lower spatial resolution
What scanning protocol best visualizes the seminal vesicles?
5mm section thickness, 5mm couch or bed index (5 X 5)
What angle is a needle reduced to for venipuncture for entering a vein?
Answer: 10 - 15 degrees also sterile technique should be used
for all injection procedures.
FYI Alcohol does not make it sterile. Betadine, start in the center,
work outward in a 3-5 inch circle, no retracing.
What type of (needle) do you use for injecting with a power injector?
18-20 gauge angiocatheter (most common). (even though we typically use 22g at CCIS for routine power injected cases)
Why is intravenous contrast utilized for Lumbar Spine CT?
Post operative … differentiate between scar tissue and
herniated nucleus pulposus material
Answer: Pre-operative… To enhance epidural veins – to evaluate
for displacement of the enhanced veins – hence bulge…
What is necessary for radiation therapy planning?
Flat table or pad, external markers, date and info on film.
Movable X, Y coordinates … NOT!
DO NOT WANT TO MOVE THE PLANE for therapy treatment
HENCE, NO MOVEMENT OF X-Y COORDINATES.
How does the couch and tube move during a spiral/helical examination?
Couch and tube move continuously, at the same time
What is an array processor responsible for?
Arithmetic computing for image reconstruction
What scanning plane best demonstrates the nasal turbinates?
Coronal
Why is it important to scan from the supraclavicular region through the
adrenal glands for CT of the chest?
Lung metastasis typically spread to adrenals vice-versa
What are the disadvantages of spiral scanning?
1 problem blooming of the effective slice thickness
i.e. Thicker slices than what the operator selected
for example: 10mm actually 12.5mm.
Increases partial volume averaging. Increased Tube heat,
Increased image noise do to addition of interpolation
Algorithm involved in the reconstruction process.
What does a Hounsfield unit represent?
Linear attenuation coefficient (scanned tissues),
CT number, absorption
What is necessary to be able to change an algorithm for image
reconstruction?
Raw or Scan Data
What is Window Width?
Total range of gray shades,
Total range of CONTRAST availability.
What is a Window Level?
Central Value (middle) of the gray scale, DENSITY of the image
What is the best position to evaluate air-fluid level in the sinuses?
Patient positioned prone, neck hyper-extended – chin up
What is an average WW and WL for an abdomen?
Any number in the ranges: 300-400 WW, 20-60 WL
What is interpolation?
Mathematical method for taking SPIRAL data and
converting into and viewing it as AXIAL images
Why is a full scanned field of view utilized for CT scanning of a spine?
A reduced display FOV is utilized for spine scanning, A full circle is utilized to acquire the scan or raw data…
Primarily to AVOID ARTIFACTS
What units are used to measure spatial resolution?
Line pairs per centimeter lp/cm
Modular transfer function (graph)
What type of contrast media (CM) may be visible as long as one year after
a CT exam?
Any oil based iodine CM or trapped barium
Oil based: same as that used for myelograms (like pantopaque)
Barium trapped in diverticula
What may occur if contrast media if IV contrast is injected into a
dehydrated patient?
Elevated creatinine, eventually hypovolemic shock
Hypovolemic shock is due to loss of volume in the vascular system
What is the 1st physical action for venipuncture?
Apply a tourniquet
What is the function of a Data Acquisition System (DAS)
boosts the signal from the detector and converts analog
(electrical) to digital information the analog to digital converter
actually does this but it is part of the DAS
What anatomical region does phlebitis most commonly occur?
CALF
What are the physical signs that an infiltration has occurred during an
injection?
Redness and Swelling
What is considered to be a reaction to venipuncture?
infection
What is considered to be a potential reaction to venipuncture?
Extravasation potentially can lead to an infection
What is the primary difference between a 512 and 256 matrix?
Number of Pixels, utilizing a 256 matrix instead of a 512
matrix technically speaking allows FASTER RECON TIME.
What kind of contrast is utilized for a suspected uterine mass?
IV, ORAL, RECTAL
What is the normal range of respirations for an adult and for a child?
12-20 per minute adult, 20-30 Child
What is the reason for fewer reactions to non-ionic vs. Ionic CM?
non-ionic does not break down into charged particles
when it enters a solution - the osmolality value is less than ionic
If a hemorrhage of Gerota’s fascia is suspected what anatomical region
would you scan?
The kidneys, Gerota’s fascia is the term given to the
Connective Tissue that surrounds the kidneys
Which of the following is a severe reaction to IV contrast?
Anaphylactic shock
What type of artifact occurs when a reference detector is blocked?
Streak artifact
Which of the following are contraindications to IV contrast?
Renal failure, multiple myeloma, pheochromocytoma,
sickle cell anemia (active) are all major contraindications and it is
difficult to determine which is worse except if renal failure is among
the choices it is your best pick.
Syncope is an indication for CT of What?
Brain
Strict breathing instructions are indicated for what studies?
Chest and abdomen
What is an indication for HRCT of the chest?
Asbestosis
What are the best cuts (parameters you choose) for reformations?
Thin and overlapping sections
What is the normal BUN range?
7-22 or 7-25 mg/dl
What does not affect contrast media flow?
The amount of contrast media injected (Viscosity, iodine concentration and temperature do!!!!)
What would be an indication for water soluble contrast?
Bowel perforation
What is the reason to know the PT lab value? PTT and Platelet count
Coagulation
All could happen but this for a biopsy of the pelvis?
Pneumothorax
How do you inject through a central venous line?
Piggyback
What is one way you could miss a 1cm tumor in the lung?
Inconsistent patient breathing
Why can’t you use x-ray barium?
Too dense, streak artifacts
What is a good window width and level for Lung tissue?
WW 1500, WL 500
What is a good window width and level for bone?
WW 3000, WL 300
What is Modular Transfer Function?
Graphical representation of SPATIAL RESOLUTION
Measured in lp/cm, tells how small you can scan without blurring.
Range for accuracy of water phantom test for CT number accuracy?
-3 to +3 CT or HU, should be done weekly,
To decrease image noise?
Increase technical factors, increase photons,
Increase dose
How do we represent image noise?
SD, standard deviation in the ROI measurement
What is the dose measurement for CT contiguous sections
CTDI Computed Tomography Dose Index
What is the worst IV injection method to image the liver?
NOT hand injection, NOT Power injection
Answer: Drip infusion
How can we decrease partial volume averaging?
Reduce voxel sixe
Reduce slice thickness, reduce FOV, increase matrix
What causes a straight black line artifact on a scout view?
Malfunctioning detector, detector is out
Where do we see beam hardening artifacts?
Most common appearance straight, black, thick line
between the temporal bone. Occurs in regions where high density
structures (such as cortical bone – near air – near tissue – near
metal implants) meet low density structures. Sudden changes in
beam energy due to the anatomy acting as “filters”. Also known as a
CUPPING artifact.
What must you do to maintain image quality when section thickness is
decreased. Example: changing from 10mm to 5mm.
Increase technical factors; produce more photons to the
smaller region. Increase mAs or kVp
Where is the data acquisition system (DAS) located?
Between the detectors and array processor
What is the function of the array processor?
Responsible for computations necessary for image
reconstruction
Which portion of the pancreas is the most common site for tumors?
The head of the pancreas. Is located apprx T-12
When should oral contrast be given for a scan of the pancreas?
Any “just abdomen CT scans” contrast should be given
½ hour prior to scanning. This allows filling of the small bowel
particularly the C-loop of the duodenum.
What is the best scanning phase for imaging the liver?
Pre-equilibrium phase.
What is the term given to the region where tracheal bifurcation occurs?
Carina
Dynamic scanning is best for?
Any situation, enhancing vs. Non-enhancing lesions.
Generally, the table is set to specific point and is not moved “zero
increment”. Contrast is injected and the area is scanned to see if
enhancement occurs. Liver hemangiomas are a great example for
this type of scanning. Peripheral enhancement “ring like” may occur
rather quickly but the central portion does not enhance immediately.
Delayed enhancement does occur.
When does the tube not move for a CT scan?
During reconstruction or for the “scout view” it remains
stationary.
What is the best way to scan a c-spine or a c-spine for a Jefferson C1
fracture?
The scanning plane: parallel to the disk space.
What is the purpose of scanning a patient prone following a myelogram?
Reduces CSF and contrast media layering.
What is the purpose of a CT request for only a scout view of the lower
extremities?
Long bone measurement also known as
orthoroentgenography.
What is represented by the standard deviation in an ROI measurement?
Image noise, IMPORTANT: Standard deviation
represents changes in CT numbers in an area. The difference
between each level of “noise” a pixel has and compares it to the
others.
What is an appropriate window setting for a pneumothorax?
1600ww, -600wl 2000ww, -200wl. Any window level
that has a (-) minus window level
What CT numbers represent acute blood?
40 - 100
What does a CT number of 0 represent?
water
What does a CT number of 1000 represent?
bone
What does a CT number of -1000 represent?
air
What does a CT number of -100 represent?
fat
Where is the jugular foramina located?
Temporal bone
What is the most common reason for a pelvic biopsy?
Endometrial CA
What type of patient consent is obtained for an unconscious patient
resulting from trauma?
Implied
What is the best way to demonstrate spondylolisthesis?
Spondylolisthesis occurs from a defect in the pars interarticulars
of a vertebrae allowing it to slip forward. A lateral
radiograph or a sagittal reformation best demonstrates the
pathology.
What is not considered to be a parenteral route of contrast
administration?
Parenteral means any route of injection (CM
administration) that bypasses the GI tract. Oral route is not a
parenteral route of CM administration.
Why are thin slices utilized for scanning the inner ear?
Increase detail or spatial resolution. Any time you use
smaller sections it increases spatial resolution. Especially, sinuses,
facial bones, any small pathology.
What is considered to be a normal platelet count?
150,000 to 400,000mm3
What are possible preps for a patient with a history of CM reaction?
Antihistamines, steroids, hydration
CT scanners ability to differentiate anatomical areas with minimal
differences in tissue and CT numbers.
Contrast resolution
What can cause hydrocephalus and where would the pathology be best
demonstrated?
A blocked foramen, foramen of Monroe. The ventricles.
What can’t be changed with retrospective reconstruction?
Scanned field of view, section thickness.
What is the best anatomical region for a bone density study (reading)?
Lumbar spine
Loss of connective tissue may cause?
Rolling veins
Metformin or glucophage precautions. When and how long do we hold?
OLD WAY: Withhold 48 hours before and after exam.
NEW WAY: take patient off right before exam, renal clearance BUN
and creatinine, 48 hours after exam is over provided renal is ok.
Name given to filter that absorbs low energy photons so they don’t cause
scatter?
Bow-tie filters
What is another name for a recon algorithm?
Kernel
What is the term used to describe the process of using a kernel or
algorithm during the recon process?
Convolution
Coronal reformations are best for?
Anything that is demonstrated the best superior to
inferior sinus air-fluid levels = direct coronal scanning = prone, neck
hyper-extended pituitary gland, tentorium cerebelli, nasal conche,
turbinates.
Delays for abd?
abd, liver up to 120 secs usually 60-80 secs
What converts light to an electric signal in a scintillation detector?
Photodiode
What effect on recon time will a change from 512 matrix to 256 matrix.produce?
A faster recon time
Change 256 to 512 will do what to detail?
better detail (increased spatial resolution)
Most common area for HNP?
L4 - L5
What is Stereotaxis?
Method of tumor localization for surgery of the brain.
When would you perform prone spine scanning?
Prevents layering of CM post myelogram CT
and CSF layering.
What is the region scanned if patient has an abnormal level of Prolactin
“Growth Hormone” with Amenorrhea?
Pituitary gland
What is the reason for using smaller sections (thin slice thickness) to scan
the inner ear?
Increase spatial resolution.
Where is the Olfactory nerve?
The Olfactory nerve “smell” comes up through the
ethmoid bone with the majority of it in the region of the cribriform
plate. Cribriform plate and the crista galli are part of the ethmoid
bone and are best evaluated in the coronal plane.
Chronic subdural hematoma would appear?
Isodense. CM would have to be injected to visualize it.
Appearance of a non-filled loop of bowel?
Tumor, abscess, obstruction. In a patient with known
Crones disease it looks like an abscess.
What is the best way to visualize aortic dissections?
Bolus injection (rate) (continuous)
What is the connective tissue termed that anchors the kidneys in the
retroperitoneal space?
Gerota’s fascia (renal fat) Wow!
X-ray photons that pass through a patient are called?
Attenuated
CT systems ability to differentiate objects with minimal differences in
tissue?
Contrast resolution.
Low soft tissue contrast
What should rectal contrast be diluted to?
2%
How should a patient be prepped with a history of prior CM reaction?
Steroids & Antihistamines
What is considered to be a severe adverse reaction to CM?
Anaphylactic Shock
What is the primary disadvantage of a power injector?
Possibility (increased) risk of extravasation.
What is the normal systolic BP range?
95-140 mm/Hg
What is the normal diastolic BP range?
60-90 mm/Hg
Child respiration rate?
20-30 breaths per minute
Adult respiration rate?
12-20 breaths per minute
Elements of Negligence MUST HAVE ALL FOUR!!!
Duty to Care, Breach of Duty, Proximate Cause, Injury.
Injury does not have to be physical.
What term represents the average CT number in a Region of Interest “ROI”
measurement?
Mean
What elements are in Solid State detectors?
Bismuth Germinate, Cadmium Tungstate, Rare Earths
What element is not used in detectors because of afterglow problems?
Sodium Iodide
What is perfusion CT used for?
Perfusion CT of the brain is the fastest modality for the early detection of acute cerebral ischemia (strokes)
Can a CT Scout image be used to measure long bones?
Yes, it can.
Where do we find Jefferson fxs?
C1 (ring fx)
