Exam IV: Radiology Flashcards
Wilhelm Conrad Roentgen
Discovered X-rays
November 8th, 1895
Received the First Nobel Prize in Physics in 1901
Early X-Ray
Light-tight cathode tube produced fluorescence of nearby chemical-coated cardboard screen
Roentgen realized that cathode ray tube emitted “something” new
“Something” passed through objects opaque to light, was invisible, and caused fluorescence
Roentgen saw bones in his hand on cardboard screen
He decided to call it X-ray for “unknown ray”
A form of electromagnetic energy with a very short wavelength of .5 to .06 Angstrom
Short wavelength allows x-rays to penetrate matter, unlike light rays
Smaller wavelength = more energy
Characteristics of X-Rays
X-rays have short wavelength, travel at speed of light, in straight path and cause ionization of matter
X-rays can be absorbed, pass through, or be scattered by tissue
Shades of gray are produced in relation to the amount of x-rays which are absorbed by the object being imaged and the remaining x-rays which reach the imaging medium
Production of X-Rays
X-ray tube consists of an evacuated glass tube with cathode and anode terminals
Cathode tungsten filament is heated to incandescence, giving off electrons
Electrons bombard positively charged anode target, and x-rays are emitted
Ionizing Radiation
Ionizing radiation is radiation that has enough energy to remove electrons from atoms or molecules.
Forms of ionizing radiation include X-Rays, Gamma Rays, Alpha particles, Beta particles and Neutrons.
X-Rays, nuclear medicine studies, fluoroscopy and CT involve ionizing radiation
Radiographs
Photographic effect of x-rays produces film image, a representation of variable tissue densities and contours
Scattered x-rays darken film and degrade image
Radio-opaque tissue is denser, absorbs more x-rays, and appears as whiter image on film
Radiolucent tissue is less dense, absorbs less x-rays and appears as darker image on film
We don’t see x-rays, we see the radiograph
Radio-opaque = basically a denser material, soaks up the energy and leaves the film white
Principles of Density
A black film would be overexposed
A white film would be underexposed
Look for different densities in any film you are reading be it plain film or CT. For example you are reading a film of the pelvis, the pelvic girdle would white, pelvic organs shades of gray, bowel gas black
Magnification Concept
The image “spreads” or magnifies causing detail to be lost
When the object creating the image is closer = more detail and closer to actual size
Film Cassette
Patients cannot hold still long enough to obtain an image from x-rays alone
Cassette contains fluorescent screens which glow when activated by x-rays and this light is used to expose the film
Less radiation and exposure times are needed
The “grid” cuts down on scatter effect on film – like a lens
Can’t use glass, so need to use lead grid “honeycomb” for x-rays to go through to focus the beam and gets rid of scattering to make a clear image
The image is taken much quicker than when it was first developed, which also clears up the image
Plain Films
What we study are radiographs, images, or films, not X-rays or electromagnetic waves
The patient is placed between the x-ray tube and the film cassette.
The body part closest to the cassette is magnified the least and has the sharpest boundaries
Positioning for Imaging
PA chest film, the x-rays pass posterior to anterior body part studied is closest to film, less magnification
Lateral films are named for part closest to the film
Posterior to anterior position: for heart and lung clear imagine (PA x-ray)
Anterior to posterior position: for spine and muscles around it (AP x-ray)
*describes the way the rays are going
Left side: for best heart image or left lung
Right side: for best right side tissues
Portable X-Ray Studies
Portable x-ray machine
Chest X-ray must be Anterior posterior (AP)
Images are never as good as in department
Limited information- not as precise
More expensive – but don’t tell the patient that
Only reason for x ray in the room: if the patient cannot leave the room
Since AP x ray, can’t see heart and lungs because it is directed towards spine and musculature
Chest X-Ray
PA (posterior to anterior)
- Radiolucent lungs
- Radio-opaque bony thorax
- Intermediate density mediastinum with important contours
Abdominal Film
KUB- kidneys, ureter, bladder
- Radiolucent bowel gas pattern
- Radiodense spine and pelvis or calcifications
- Intermediate density soft tissue viscera with important contours
Digital Radiography
No actual “film” is required
X-rays strike a phosphor plate and a photomultiplier intensifies the image.
Data is recorded in a digital format, just like digital photography
Resulting image can be viewed on a monitor screen or can be transferred to radiographic film
Digital allows to send it anywhere, make many copies, and easier to store
Advantages of Digital Radiography
Digital images require less storage space
Multiple monitors can look at the same image at the same time
Much more difficult to “lose the films”
Images can be transmitted electronically and copies are easily generated.
The view that is generated can be altered by the computer (Contrast and Brightness)
Disadvantages of Digital Radiography
Hospitals already have fully functional film based imaging equipment and film library
The new equipment is expensive – you cannot read diagnostic studies on a simple computer monitor
Images may not quite as sharp and precise
Fluoroscopy
Common radiological technique that allows real-time visualization
A continuous beam of x-rays pass through the patient to form an image on a fluorescing screen which is amplified electronically and viewed on a television screen
Common procedures include: Upper GI, Lower GI (barium enema) and many interventional procedures
X-ray tube is below patient
Film changer and image intensifier above patient
Table can be tilted, patient can be rolled side to side
Contrast Media
Any substance that is radio-opaque will absorb x-rays and show up as white in radiographs
Different types of contrast material can be given orally, rectally, intravenously or injected into a specific space
All forms of contrast have advantages and disadvantages
GI Contrast
Outlines structures in the GI tract
Can be administered from either end, depending on what you want to see
Barium sulfate or iodinated water soluble
Goes into the GI tract, stays in the GI tract – is not absorbed
Barium Sulfate
Type of GI contrast
Barium sulfate Extremely dense, provides good images Slow to be excreted - sticky stuff Contra-indicated where spillage into a body cavity is possible Must be dilute for CT scan – Redi Cat® Tastes terrible
Iodine Based Water Soluble Contrast
Type of GI contrast
Iodine based water soluble contrast
OK if spilled into peritoneum or mediastinum
Somewhat less dense, therefore gives slightly less detail
Toxic to lung tissue, must be used carefully if there is a risk of aspiration
Tastes terrible
IV Contrast
Allows precise imaging of blood vessels or urinary tract
Shows shape of vessels and any extravasation
Iodinated compounds are most common, carbon dioxide can be used for angiography
Materials containing Iodine are toxic to the kidneys
Goes into the bloodstream, excreted in urine, does not transfer to any other location
No taste
Shows leaks (extravasation) and spaces of urinary tract Why do we choose CO2? Most other gases are dangerous (N for example can prevent heart from beating), CO2 is instantly removed from the body (O2 is slower) because attaches to Hb and taken out of circulation
Examples: Renal Artery Arteriogram and Intravenous Pyelogram
Digital Subtraction Angiography
Initial image to identify surrounding structures
Repeat images with IV contrast have static portions of image removed
Clarifies images of structures being studied
Characteristic appearance
Skull is very dense, so getting a clear picture of arteries using x rays= hard
No contrast photo than photo with contrast and the computer subtracts the first image from the second one
Ultrasound (US)
Narrow beam of high frequency sound waves is produced by a vibrating crystal
Sound waves are directed into the body and reflected back dependent upon tissues differing acoustic impedance
The crystal in the transducer acts as a transmitter and a receiver
Crystal that gives off and receives wanes and get photo from it
Acoustic impedance: how sound “bounces”
The tech’s hand is controlling the transmitter and receiver (acts as both)
Image Formation: US
The transducer records echoes reflected back when the sound wave strikes an interface between two tissues that have different acoustic properties
This data is then analyzed by a computer to create a digital image
Ultrasound can displayed as static images or as multiple video images that permit movement in real time
US works well with fluid filled cavities
Echogenic Ultrasound
Images are based on internal echoes due to acoustic interfaces
May be described as hypoechoic, isoechoic, or hyperechoic
Solid tissue, tumors, fat or fibrous tissue show as light areas
Anechoic – echo-free due to absence of acoustic interfaces; no sound interfaces
Sonolucent - cyst or fluid-filled viscus shows as a dark area
Acoustic Shadowing: Echogenic objects have differing amounts of acoustic shadowing – This may be described as “characteristic”
Advantages of US
No ionizing radiation – freely used in obstetrics, pediatrics, and multiple evaluations
Safe - no evidence as yet to indicate adverse effect on human tissue at intensity level currently used
Multi-planar imaging – axial, sagittal, oblique planes
Ability to differentiate cystic, solid, and complex tissue
Cost-effective (cheap)
Easily portable
“Real-time” analysis and procedures
Disadvantages of US
Air and bone produce extreme acoustic impedance; most sound is reflected prohibiting sound penetration
Images not as clear as CT or MRI
Very operator dependent- clarity of objects/objects’ views
Ultrasound Guided Biopsy
Ultrasound-guided biopsy of a breast mass for example
Shows the needle entering, inserting, and exiting the tissue
Doppler Ultrasound
Ultrasound of abdominal aorta for example
Doppler effect is used to calculate the velocity of the moving blood
Wave form at bottom shows changes in velocity
Checks the speed of the sound wave before and after and based off of the velocity can tell how fast something is moving, especially for a fluid
Also color Doppler US, where color is added via computer
Computed Tomography (CT)
CT produces cross-sectional images by scanning a slice of tissue from multiple angles with a narrow X-Ray beam
The computer then calculates the amount of radiation absorbed at each point in the rotation for the various elements in the tissue that was scanned
It then displays the CT reconstructions as a gray scale image on a monitor
Older name for CT: Computed Axial Tomography (CAT)
CT: How the Image is Created
Electrical pulses are analyzed by a computer and the x-ray absorption for each voxel of body is calculated, producing image of black, white, and varying shades of gray
Involves higher level math– the most complicated Sudoku you ever imagined
A picture is then created where very dense tissues are white (bone), intermediate dense tissues are gray (liver), and least dense tissue is black (air)
Images can be viewed on a screen or printed on specialized x-ray film
Usually printed on film for storage
Spiral CT
A newer technology, it is faster and can be used to develop three dimensional reconstruction in planes other than axial
Then patient moves through at constant speed as it continuously rotates to take slices
Continual CT scanning is performed as patient moves through the gantry
Requires an entirely different (and more expensive) type of scanner
Multi-Slice CT
Next generation scanners perform multiple slices per rotation and provides software programming for instantaneous three-dimensional images
Extremely fast scans
Newer and more expensive machinery
Spiral scanner, but get several individual slices at once
Advantages of the CT
CT is extremely sensitive to slight differences in tissue density(1%)
In comparison screen or film radiography requires at least a (5%) difference
Gives excellent images and a wealth of information
Available in some form in nearly any hospital
Disadvantages of the CT
Expensive
High demand may mean a long wait for imaging studies
Ionizing radiation
Could be considered “over utilized”
CT Contrast Media
IV contrast
Helps to differentiate vascular from nonvascular structures
Differences in the degree of contrast over time helps characterize lesions
Also helps define structures in urinary tract
Oral contrast
Helps to delineate the GI tract- stays in GI tract
Must not be too dense
Barium is too dense- best for only a single image taken at a time; we can’t use this for a CT because the CT is too complex
Basic Rules of Orientation
No matter what imaging method is involved or what part of the body you are looking at, if the image is axial it should be displayed the same way
The patient’s right side to your left and vice – versa
Anterior is up, posterior is down
Manipulation of CT Images
CT images can be manipulated to enhance visualization of lung parenchyma, mediastinum or bone by changing “window” settings
CT scanner has buttons for lung, heart, etc. windows to see those structures better
Example: lung window.. Can’t see bone as well or other things
3D Imaging
Produced by “stacking” contiguous images from individual slices (CT)
Even more higher level math
Involves image averaging which gives limited detail
3D fracture reconstruction is particularly useful for orthopedic surgery
3D CT Angiography
Magnetic Resonance Imaging (MRI)
Essentially imaging of protons
Patient lies on a gantry within a magnetic field
Hydrogen protons align themselves within the external magnetic field
They then absorb energy from broadcast radio waves
When the broadcast stops the protons send out new radio waves that can be detected and converted to images based on how many protons are present in any given area
Signal intensity reflects number of hydrogen atoms
Bones- not much detail because don’t contain water
MRI: T1 vs. T2
If the radio receivers listen early when the protons broadcast they create images called T1 weighted , if they listen later during the process the images are called T2
Image is determined by H+ atoms or water content, not tissue density as with x-ray
Terminology includes high or low signal, not radiolucent or radiodense
One scan can produce images in multiple planes
Use T1 vs. T2 depending on what you want to see
When you order a scan, must pick T1 or T2 scan, not both simultaneously
CT scans can produce different windows from one image… MRI you can’t produce multiple images, only have T1 scan or T2 scan
MRI: Gadolinium Contrast
Gadolinium is a rare earth element with atomic number 64
It is magnetically active and can be used to enhance contrast between tissues, especially in T1 images
It is injected into the bloodstream during the procedure and helps with imaging tumors, infections, and acute stroke
Example: MR Angiography
Advantages of MRI
No ionizing radiation
No known health hazard
Multi-planar – axial, sagittal, coronal, oblique and other angles.
Soft tissue contrast is excellent
Less affected by patient’s body habitus
Gadolinium – contrast utilized, well tolerated
Bigger person can still get good images with MRI, unlike x-ray
X ray- the bigger the person the more energy and the image is not clear and all white
Disadvantages of MRI
Long scanning times
Claustrophobia – “Open MRI” images do not give the same detail as closed tube
Contraindicated with pacemakers and ferromagnetic materials
Non-ferrous metals interfere with image quality.
Respiratory and cardiac motion are problematic
High cost
CT vs. MRI
CT images are produced by X-rays, MR images are produced by magnetic fields.
CT/x-ray contrast agents include barium sulfate or iodinated compounds, MRI uses gadolinium
Fat in MRI appears white, Bone in CT appears white
CT is excellent for bone, MRI is excellent for soft tissue
Uses for CT vs. MRI
Common indications for CT imaging:
Trauma, intracranial hemorrhage, fracture detection and evaluation, spine alignment, detect foreign bodies in joints, dx of primary and metastatic neoplasms, the gold standard for axial images
Current uses of MRI:
Has become the modality of choice for non urgent imaging of the central nervous system and spine
Also first line of imaging for most conditions of musculoskeletal system
Good for soft tissue injuries of knee, ankle, shoulder
Long term back pain, psychological issues, muscle, tendon, cartilage, anything other than bone
Nuclear Medicine
In radiography ionizing radiation pass through the tissue to produce an image
In Nuclear Medicine the patient ingests or is injected with a radiopharmaceutical that emits radiation and an image is created from the Gamma radiation emitted from within the patient
Radioisotope Scanning (Nuclear Medicine)
Radioactive isotope is given intravenously or by mouth and uptake is imaged with a gamma camera
Nuclear Medicine Procedure Types
Radioisotopes such as technetium are bound to a chemical substance which normally accumulates in a specific organ
TC attachment to – thyroid, bone, lung, etc.
Patients red or white blood cells can be “tagged” to scan for bleeding or infection
RBCs can see where you are bleeding
WBCs can see where you have an infection
Nuclear Medicine Contrast
The amount of ionizing radiation to the patient is similar to that in a plain radiograph
The injected radionuclide does not produce the side effects or complications seen with radiographic iodinated contrast agents
The physiologic map images produced by some nuclear medicine procedures allows change to be detected earlier than plain radiographs
No worse than having an x ray, actually better than iodine contrast
Nuclear Medicine: Organ Physiology
Abnormal radionuclide images demonstrate hot spots (increase in uptake) or cold spots (decreased uptake)
Images are excellent for documenting organ physiology but lack in anatomic information
Plain film studies can be useful for correlative purposes
Can do an x-ray and nuclear study and compare them
Thyroid nodule, bone scans, etc.
Pulmonary Embolism: see an area of less perfusion (small and big areas) that tells us that blood flow is affected- can’t see this on an x ray
Could see on simple CT of chest or arteriogram is large enough, perfusion scan is best way to dx
Hepatobiliary Iminodiacetic Acid or HIDA Scan
HIDA is injected, IV, excreted by liver into biliary tree, enters the gallbladder and flows into the bowel
With cholecystitis, the cystic duct is blocked, and there is no visualization of the gallbladder, even on delayed images
Normal: at 15 minutes can start to see gallbladder, at 20 minutes the gallbladder is larger
Abnormal: shows that the gallbladder is not filling and is abnormal
Cannot see this on CT or MRI, only with nuclear medicine
Sentinel Lymph Node Scan
Used in Malignant Melanoma and Breast Cancer Cases
Allows removal of the first lymph node that drains the tumor site
Designed to go into lymphatic system
Breast cancer and melanoma – both spread to lymph nodes easily and so should remove these
If we know where the tumor is you can find the lymph nodes that are affected because it drains to those ones
Single Photon Emission Computed Tomography (SPECT)
Specialized gamma camera rotates around the patient to produce a tomographic image
Used in cardiac imaging, cerebral perfusion scans
Radio tracer in the blood and taking sliced images of that
Shows blood flow
Positron Emission Tomography (PET)
Evaluates how cells use glucose
Fluorodeoxyglucose (FDG), a radioisotope, is given to patient, concentrates in tissue according to metabolic rate
Breaks down to produce gamma rays (Positron Emission)
Can be detected by a PET CT scanner for 3D images
Takes specialized sugar and attach FDG to it, and when broken down/metabolized it gives off radiation
Shows how much glucose is being broken down
PET Uses
Oncology - utilized to evaluate for metastatic disease and for post therapy follow-up evaluation
Cardiology - screening for coronary artery disease and myocardial perfusion
Neurology - stroke evaluation and to identify epileptic foci for surgical intervention
Potential future uses are too numerous to list
Examples: Lung cancer staging, responses to therapies (cancer especially), myocardial viability
