Lab 1 & 2 (Q1) Flashcards
(84 cards)
1
Q
What is the Inverse Square Law?
A
X-ray intensity DECREASES w/ distance from the tube
2
Q
How exactly is X-ray intensity related to distance from the tube?
A
- Decrease in intensity is proportional to the square of the distance from the source
- Is an expression of energy conservation
- Small differencess in FFD may alter the image substantially
3
Q
Distance from the X-ray tube affects film _________.
A
Blackness
4
Q
When focal-film distance (FFD) _________, film blackening decreases due to _________ intensity of the X-ray beam and vice versa.
A
- Increases
- Decreasing
(FFD and film blackening are INVERSELY related)
5
Q
What happens to the image if you take rads at 32 inches (80 cm) instead of 40 inches (1 m)?
A
- Increase the beam intensity by 56% & overexpose the image.
_I1 _ = (d2)2
I2 (d1)2
6
Q
Why type of radiation is X-ray?
(2)
A
- Electromagnetic radiation
- Ionizing radiation
7
Q
ID the parts of an X-ray tube
A
8
Q
Increasing the ___1___ increases the potential difference btwn the filament and the ___2___
and electrons are accelerated to higher __3__ and have more __4__ when striking the target.
A
- kVp
- target
- velocities
- energy
9
Q
Which type of radiative interaction at the target/anode
creates the majority of the X-ray spectrum used?
A
Bremsstrahlung radiation
(braking radiation)
10
Q
What 2 things effect scatter?
A
- Patient’s size
- Size of exposed area
11
Q
How can you prevent scatter?
A
- Expose only as much as necessary (collimation)
- Utilize a grid
- Air gap technique
12
Q
At what point should you always use a grid to prevent scatter?
A
for any structure > 10 cm
13
Q
Why is it NOT practical to reduce scatter by lowering the kVp?
A
Low energy x-rays are readily absorbed by the pateint & radiation exposure is increased
14
Q
How is image contrast affected by the energy of the X-ray beam?
A
due to the Photoelectric effect (PE)
15
Q
Describe the Photoelectric Effect.
A
- form of interaction of an X-ray w/ matter
- low energy photon interacts w/ the e- in the atom & removes it from its shell → removed e- = photoelectron
- It is related to the atomic number of the attenuating medium (Z)
- PE =Z³
- Inversely proportional to the third power of the photon energy
16
Q
When will the PE be greater, at lower beam energy or higher beam energy?
A
Lower beam energy
17
Q
How can you control Image Contrast?
A
High mAs/Low kVp settings increase tissue contrast
18
Q
Which tissues would you use Low mAs/High kVp setting?
Why?
A
- Tissues w/ inherent tissue contrast (i.e. thorax)
- To avoid too high a contrast and achieve a wide lattitude
19
Q
What is Ultrasound?
A
Sound waves w/ a frequency higher than the upper range of human hearing .
(Human hearing = 20 kHz vs. Diagnostic U/S = 2 to 10 MHz)
20
Q
What is the unit of measurement for U/S?
A
HERTZ!!!
- 1 Hz = 1 cycle per second
- 1 kHz = 1,000 cycles per second
- 1 MHz = 1,000,000 cycles per secong
21
Q
What is the audible range of human hearing?
A
20 Hz to 20kHz
22
Q
What is the range of Infrasound?
A
< 20 Hz
23
Q
What is the range of U/S?
A
> 20 kHz
24
Q
List & define the 4 properities of U/S waves!
A
- Frequency (f) ⇒ # of sound waves per second
- Wavelength (w) ⇒ distance that a sound wave travels during one cycle
- Speed ⇒ f x w
- Amplitude ⇒ intensity of the wave
25
What is the relationship btwn Wavelength, Resolution and Penetration?
* **Short** wavelength ⇒ **High resolution**, Low penetration
* *Long* wavelength ⇒ Low resolution, *High penetration*
26
What happens to the penetration if you try to improve resolution by increasing the frequency?
Decrease penetration
27
How should you select a transducer?
Always choose the **highest frequency** (resolution) that will penetrate
to the depth needed for the particular shot.
28
How should you set the **Power** (Intensity, Output) setting on the U/S?
Why?
* Should be set as low as possible
* Will allow the best resolution & prevent artifacts
29
What does the **Gain** setting on the U/S control?
Amplification of the returning echoes
30
What is **echogenicity**?
What are the 4 different terms used to describe echogenicity?
* the extent to which a structure gives rise to reflections of ultrasonic waves.
* Anechoic, Hyperechoic, Hypochoic, Medium Echogenicity
31
Which anatomical structures are **Anechoic** (produce no echo/are black) ?
* Veins
* Arteries
* Gallbladder
* Bone (with a hyperechoic rim)
* Lymph nodes
32
Which anatomic structures are **Hyperechoic** (creates a strong reflection back/appears bright)?
* Bladder stones
* Gas in the stomach
* Spleen
* Fascia
* Ligaments
* Tendons
* Pleura of the lungs
33
Which anatomical structures are **Hypoechoic**?
* Liver
* Cartilage
* Muscles
* Lymph nodes
34
Which anatomical structure has medium echogenicity?
Spleen
35
What is acoustic **enhancement**?
* Characteristic interaction of sound w/ **fluid**.
* An area of increased brightness underneath fluid resulting from the lack of impedance when sound waves pass through fluid and increased echoes from underlying structures.
36
What is acoustic **shadowing**?
* Characteristic interaction of sound w/ **mineralized material**
* Causes a signal void behind structures that strongly absorb or reflect ultrasonic waves
* Happens most frequently with solid structures, as sound conducts most rapidly in areas where molecules are closely packed, such as in bone or stones.
37
What is Reverberation?
* An artefact of the interaction of sound w/ gas
* Occurs when ultrasound bounces between two highly reflective surfaces. The waves will move backwards and forwards btwn these interfaces. The machine recognizes these waves as parallel lines with equal distances between them
38
What happens when sound waves interact w/ soft tissue?
Why?
What effects this?
* Become ATTENUATED
* Loss strength b/c some waves are transmitted & some are reflected back to the transducer
* Distance traveled, type of tissue & frequency of the sound waves
39
List the possible ultrasound artifacts that can be encountered.
* **Acoustic shadowing**
* **Acoustic enhancement**
* Edge shadowing
* Mirror image
* Reverberation (comet tail, ring-down)
40
What type of areas does acoustic shadowing cause?
How does it appear?
* Hypoechoic or Anechoic areas
* As a dark band deep to the gas containing, bone mineral or metal structures
41
How much of the incoming sound beam is reflected by gas?
99%
42
How much of the sound waves are reflected by bone?
20-30%
43
How can acoustic enhancement be useful to the U/S user?
May help differentiate cysts from solid hypoechoic nodular lesions
44
How does edge shadowing (A.K.A refraction) occur?
* Occurs deep to the edge of curved surfaces of round or oval structures which refract the beam
45
How do mirror image artifacts occur?
* occur on rounded, strongly reflective interfaces (ex. btwn lungs & diaphragm)
* Causes "duplication" structures
46
What causes a "Comet tail"?
How is it formed?
* A narrow band of reverberation
* Caused by small echos (metallic structures & gas bubbles separated by fluid)
47
What is a "Ring-down"?
What causes it?
* Type of reverberation
* Occurs when a sequence of repetitive hyperechoic lines are displayed on the screen
48
List Non-Ferrous metals.
* Alloys: brass
49
List Ferrous metals.
| (Will be attracted by the magnet)
* Aluminum
* Copper
* Zinc
* Lead
* Nickel
* Tin
* Titanium
50
What is a Faraday cage?
* An enclosure formed by Copper mesh that blocks external static & non-static electric fields
* Provides constant voltage on all sides of the enclosure
51
What is the effect of external electric fields on the inside of a Faraday cage?
External electric fields are cancelled out on the inside of the cage
(electric charge inside = 0)
52
Which alignment, aligned w/ the magnetic field or opposite to the magnetic field, has more energy?
protons aligned OPPOSITE to the magnetic field have slightly more energy
53
Which protons create the **net magnetization vector** and generate the MR signal?
the small excess of protons aligned with the magnetic field
54
What happens to protons in **T1 MRI mode**?
protons regain order and return to their original vertical orientation
(pointing up)
55
What happens in **T2 MRI mode**?
protons lose their order and are oriented horizontally (→)
56
When does **Resonance** occur?
when the net magnetization vector rotates toward the X-Y plane
& protons spin *in phase*
57
What pulse applied at l*armor frequency of H+ protons* and *perpendicular* to the main magnetic field causes the magnetization vector to **ROTATE out of alignment** & towards the X-Y plane?
Radiofrequency (RF) pulse
58
Does the Radiofrequency pulse cause a gain or a loss of energy?
Why?
* A gain of energy
* b/c more H+s align *against* the main magnetic field
59
What does the **flip angle** depend on?
on the strength & duration of the applied RF pulse
60
What flip angle is refered to as a transverse plane?
90°
61
What is the component of the net magnetization vector
*perpendicular* to the main magnetic field call?
Transverse magnetization
62
What is the component of the net magnetization vector
*parallel* to the main magnetic field call?
Longitudinal magnetization
63
What 3 things occur simultaneoulsy once the RF pulse is turned off?
1. Absorbed energy is re-transmitted at the resonance frequency
2. Spins begin to return to orginal longitudinal orientation → **T1 relaxation**
3. Protons that were in *in-phase* begin to *de-phase* → **T2 relaxation**
64
What are other names for **T1 relaxation**?
* Longitudinal relazation
* Spin-lattice relaxation
* T1 recovery
65
**T1** referes to the time it take 63% of _________ magnetization to recover.
Longitudinal
66
Photons ________ their engery during **T1 relaxation**.
give up
67
Photons ______ their energy during **T2 relaxation**.
share
68
**T2** is the time it takes 63% of _________ magnetization to be lost.
transverse
69
What determines the overall magnetization of the nuclei during **T1 & T2 relaxation**?
the sum of the vectors from all individual nuclei
70
How quickly is **longitudinal magnetization** (T1)
regained in fat? In H2O?
* Fat = quickly
* H2O = slowly
71
How quickly is **transverse** magnetization (T2) lost in fat? H2O?
* Fat = quickly
* H2O = slowly
72
What are **T1 Weighted MRI**'s good for?
What do they demonstrate?
* Visualizing anatomical detail & differentiation btwn different tissue types
* Demonstrates differences in the T1 relaxation times of different tissues
73
How does fat and fluid appear on a **T1 Weighted MRI**?
* Fat = bright
* Fluid = dark
74
How does fat & fluid appear in **T2 weighted images**?
* Fat = intermediate to bright
* Fluid = Bright
75
How do the different tissues appear in
**Proton Density Images**?
* Fat = very bright
* Grey matter = brighter than white matter
* CSF = intermediate signal strength (grey)
76
What are **Proton Density MRIs** useful for?
Evaluating tissues w/ low signal intensities
(**bone & connective tissue**)
77
Which type of relaxation is used to generate
FLAIR & STIR images?
Inversion Recovery
78
What does FLAIR stand for?
Fluid Attenuated Inversion Recovery
79
What does STIR stand for?
Short Tau Inversed Recovery
80
How will the different tissues appear on **FLAIR**?
* Fat = bright
* White matter = grey scale
* Grey matter = grey scale
* CSF (free fluid)= black
81
What is **FLAIR** best used for?
* FLAIR →nulls fluid→ spine
* To detect hyperintense lesions (i.e. brain edema) that are directly adjacent to fluid filled structures (i.e ventricles of the brain) & is especially useful when those changes are subtle
82
How will the different tissues appear on **STIR**?
* Fat = black
* CSF, Grey matter & White matter = grey
* CSF \> GM \> WM (brightness)
83
Why are **STIR** images useful?
* Nulls out the fat signal & allows fluid due to pathology to be visualized in regions w/ high fat content (ex. orbits of the eye)
* Can see bone bruises or bone edema
84
What is the effect of slice thickness on reconstructed **CT** images?
Thin slices = better image & better resolution
