*Radiology Flashcards
1
Q
MOST SUSCEPTIBLE
organs to cancer induction
A
- bone marrow
- colon
- lung
- stomach
2
Q
MOST COMMON CANCERS TO
METASTASIZE TO THE FOOT
A
- breast
- prostate
- lung
- kidney
3
Q
Moderately susceptible
organs to cancer induction
A
- bladder
- breast
- liver
- esophagus
- thyroid
4
Q
are children or adults more susceptible to cancer induction from radiation?
A
children
because children have more cells that are growing and dividing rapidly, their organs and tissues are growing, and they have a longer lifespan ahead of them, giving cancers more time to develop.
5
Q
ALARA
A
“As Low as Reasonably Achievable”
for radiation protection, minimize the imaging doses when possible
6
Q
radiation protection
methods
A
- ALARA - “as low as reasonably achievable”
- Exposed personnel monitored by film badge
- lead shielding and increasing distance from the source
- shielding within the room
7
Q
difference in level of ionization between:
radiographs and CT
A
CT has much higher level of radiation than radiograph
8
Q
general position for x-rays
A
- weight-bearing
- angle and base of gait
- Feet ABducted 15 degrees
- Medial malleoli 2” apart
9
Q
Kilovoltage peak
(kVp)
A
contrast or gray scale
increasing kVp → more penetrating x-ray w/ increased latitute, shorter exposure time, less x-ray tube heat
increasing kVp = less exposure to patient
10
Q
milliamperage (mA)
A
Quantity / Density
- controls quantity or amount of x-ray emitted from the x-ray tube
- *most important factor controlling radiographic density
reduce radiation exposure by reducing mA
11
Q
exposure factor:
distance
A
fidelity
- fidelity: true size/shape of original object)
- to achieve maximum fidelity, distance of object to film must be kept to a minimum
small focal spot (decreased distance) = better detail
12
Q
Compton effect
A
occurs when x-ray photon interacts w/ an outer shell electron
occurs mostly above 80 kVp
causes less radiation to patient and is detrimental to image
13
Q
grid
A
composed of alternating strips of lead and aluminum spacers to control, by absorbing, scatter radiation
14
Q
collimation
A
method of limiting the area of an xray beam, which by law cannot exceed film size
light beam from collimator maps the area of the x-ray beam
15
Q
photoelectric effect
A
occurs at lower kVp when an xray collides with a lower shell electron
the electron is ejected and another higher shell electron fills its space, releasing energy
photoelectric effect is beneficial to image, but results in greater absorption of radiation of patient
16
Q
orthoposer
A
the platform that enables weight-bearing images of the foot and ankle to be obtained
x-ray film or image receptors on the orthoposer can lie flat or be placed vertically
17
Q
hard x-rays
A
produced by increased kVp
- higher energy (photon energies above 5-10 kVp)
- short-wavelength
- high frequency
- increased penetration
- less dangerous to the patient
18
Q
soft x-rays
A
produced by decreased kVp
- long-wavelength
- low frequency
- low penetration
- lower energy
- more dangerous to patient
19
Q
difference b/w CR and DR
A
- Computed radiography (CR) - uses a reusable CR-specific cassette instead of standard x-ray film; image on cassette is run through the CR reader, where the image is scanned into digital format
- Digital radiography (DR) - transfers the x-ray directly into a digital signal
20
Q
what determines film speed?
what does film speed affect?
A
size of the silver bromide (AgBr) crystals
larger the size of the AgBr crystals → the thicker the emulsion layer
faster the film → darker the image
21
Q
x-ray machine requirements
(vary by state)
A
- dead-man type exposure switch w/6-foot cord
-
machines < 70 kVp do not need 1-2 degree barriers or special lead-lined rooms
- the majority of podiatric x-rays are taken below 70 kVp
- lead aprons, gloves, and goggles are 0.25 mm thick
- gonadal shields 0.5 mm lead equivalent
22
Q
relative radiographic densities
from highest density → lowest
A
cortex - cancellous - muscle - nerve - tendon - ligament - subq - fat - air
23
Q
order from LEAST to MOST dense:
tendon, muscle, ligament, nerve, sub q
A
- subQ (least dense)
- ligament
- tendon
- nerve
- muscle
24
Q
DP
foot position
A
- central ray aimed at 2nd met-cuneiform joint
- 15° from vertical
when examining foot for a foreign body, this view may be taken perpendicular for better spatial location
25
Lateral
foot position
* **_medial_** side of foot against film
* central ray aimed at **_cuboid_**
* tube is **_90°_** from vertical
26
NWB Medial Oblique
foot position
* center beam at **_3rd metatarsocuneiform_ joint**
* angle the foot **_45_° w/ the _medial_ side** of the foot on the image receptor
27
NWB Lateral Oblique
foot position
* central ray aimed at **_1st metatarsocuneiform_ joint**
* angle the foot **_45_°** w/ the **_lateral_ side of the foot on the receptor**
28
Stress Lateral /
Stress Dorsiflexion
foot position
* position patient for lateral, but then have patient **flex knees** and **maximally dorsiflex ankle**
* *\*(aim at cuboid w/ medial side of foot against film)*
* demonstrates any **anterior ankle impingement** (osseous equinus)
29
Plantar Axial
foot position
* head angled at **_90°_** to the vertical
* central beam aimed at **plantar aspect of the sesamoids**
* toes dorsiflexed against film and then raise heel
* positioning device may aid in taking this picture
\*good view of **sesamoids** and **plantar aspect of metatarsal heads**
30
Harris-Beath
(SKI-Jump)
foot position
* patient stands on film w/ **_knees and ankles flexed 15-20°_**
* first, take a **scout lateral film** and determine the declination angle of the posterior facet of the STJ
* then, take 3 views: one at the angle determined by lateral film, one 10° above, and one 10° below
* (some advocate 3 arbitrary views at 35, 40, and 45 degrees)
31
good view of both the **sesamoids** and **plantar aspect of metatarsal heads?**
**plantar axial view**
32
good view for **posterior and middle STJ _coalitions_?**
Harris-Beath view
33
good view for assessing **middle and posterior STJ _facets_**
Calcaneal Axial view
34
Calcaneal Axial
foot position
* central ray aimed at **posterior aspect of _calcaneus_**
* angle central beam at **_45°_**
Examines calcaneus for fractures, abnormalities in shape, or internal fixation in major tarsal fusions
Also a good view for assessing middle and posterior STJ facets
35
ISHERWOOD views
foot position
* 3 positions to fully visualize the STJ
* Includes:
* Oblique plantardorsal view → visualize anterior facet
* Medial oblique axial → visualize middle facet
* Lateral oblique axial → visualize posterior facet
36
Isherwood view 1:
Oblique plantardorsal view
Visualize Anterior facet of STJ
* foot is positioned the same as for a NWB medial oblique x-ray
* central ray aimed **b/w fibular malleolus and cuboid**
37
Isherwood view 2:
Medial Oblique Axial
Visualize Middle facet of STJ
* foot **_adducted 30°_** from image receptor
* **dorsiflex and invert** the foot using a sling
* central ray aimed **b/w fibular malleolus and cuboid**
* tube head angled **10° cephalad**
38
Isherwood view 3:
Lateral Oblique Axial
visualizes Posterior facet of STJ
* foot **ABducted 30°** from image receptor
* dorsiflex and evert the foot using sling
* central ray b/w **_tibial_ malleolus and _navicular_ tuberosity**
* tube head angled **10° cephalad**
39
Stress Inversion
(talar tilt)
assess lateral ligamentous injury, specifically the ATFL and CFL
* position same as ankle AP view
* Examiner wears lead gloves
* stabilize lower leg w/ one hand while forcefully inverting foot w/ other hand
40
Stress Inversion
indication and positive
* indicated to assess lateral ligamentous injury, specifically of the **ATFL and CFL**
* performed after ankle **inversion** sprains;
* may need to anesthetize foot for pain relief and to relax foot
* (common peroneal block)
Positive if **greater than 10°**, or if the **talar tilt is 5° greater than the unaffected** ankle
41
Anterior Drawer
(push-pull stress)
foot position
* pt is **supine or sitting w/ leg in lateral position**; stabilize leg w/ one hand and place anterior dislocating force on the foot w/ the other hand
* central ray aimed at **medial malleolus**
42
Anterior Drawer
(push-pull stress)
purpose and positive value
* taken following ankle trauma to assess the ATFL
* good visualization of the tibial plafond and medial space b/w medial malleolus and body of talus
* lateral space b/w lateral malleolus and talus cannot be visualized
* Positive test: **6 mm or greater gap** b/w posterior lip of tibia and the nearest part of the talar dome
43
Ankle AP
* foot positioned straight ahead
* central beam **parallel** to the floor and aimed **b/w malleoli**
* good visualization of the tibial plafond and medial space b/w the lateral malleolus and talus, may not be visualized
44
Lateral Ankle
* medial side of foot against film
* central beam **parallel** to floor aimed at **center of the ankle**
* good for trochlear surface of talus and its articulation with the tibia and fibula
45
medial oblique ankle
* leg **internally rotated 45°** from the central beam
* medial side of foot against cassette
* central beam parallel to floor aimed at **center of the ankle**
* good view of tibiofibular syndesmosis
46
lateral oblique - ankle
* **lateral** side of foot against the cassette
* leg **externally rotated 45** degrees from the central beam
* central beam parallel to floor aimed at **center of the ankle**
47
Mortise view
* leg **internally rotated ~15 degrees** from central beam, and attempt to **place the malleoli on a plane parallel to film**
* central beam parallel to floor aimed at **center of the ankle**
* the arch formed by the tibial plafond and the 2 malleoli is referred to as the ankle mortise
* (this view is intended to adequately visualize the mortise)
48
Canale view
* view is same as A/P view, but the foot is fully **PLANTARFLEXED** and **PRONATED 15°**
* provides a good view of **talar neck for fractures in this area**
49
Broden I view
foot position
* ankle at **90°** and the foot is **ADDucted 45°**
* central beam aimed at
* 4 cephalad views at 10° intervals off the perpendicular
* 40, 30, 20, 10 cephalad
50
Broden I View
indication
allows visualization of the middle and posterior STJ facet, useful in comminuted fractures of the calcaneus
* **40°** projection shows **anterior portion** of the posterior facet
* **10°** projection shows **posterior portion** of posterior facet
* middle facet can be seen at best at either 20 or 30
51
Broden II View
allows visualization of **depressions in the posterior facet** of the STJ
* xray beam is tilted 15° caudally
* 3 projections at 3-4° intervals
52
MRI
overview
* imaging modality that uses the **body’s natural magnetic properties** to generate detailed images.
* **noninvasive** and uses **_no_ ionizing radiation**
* Average magnetic field strength is between **0.2 and 3 T** (Tesla)
* Open MRIs are available for patients who are claustrophobic; these units have less field strength
53
MRI
how it works
* uses body's hydrogen molecules
* also abundant in water and fat
* in ionic state, it's a positively charged and has a magnetic spin or wobble → all protons wobble in a chaotic manner and cancel out magnetism
* by applying large external magnet, the (H+) protons in the body align w/ MRI's magnetic field
* once aligned, radio frequency pulse is applied → pushing protons to higher energy level
* radio pulse is turned off → higher energy gained by protons (nuclear magnetic resonance signal) → dissipated and is transmitted to the receiver coils
* radiofrequency coils act both as transmitter and receiver
* protons realign at different speeds and produce different signals
54
T1 imaging
“anatomic images”
* measuring the **time taken for the magnetic vector to return to its resting state**.
* produce hyperintense (brighter) signal with fat, bone marrow, nerves, and lipomas
55
T2 imaging
“pathologic image”
* produced by measuring the **time needed for the axial spin to return to its rest state**
* produce hyperintense signal with water (inflammation), blood, edema, and fluid-filled tumors
* Most diseases manifest themselves by an increase in water content (inflammation)
56
STIR
(Short-T1 Inversion Recovery)
used to **nullify the signal from fat** to allow greater visualization of other tissues
* a type of fat suppression
* the high signal produced by fat can mask subtle contrast differences, which can mask pathology
57
MR Arthrography
* Used primarily in the shoulder and hip.
* Involves injecting a contrast material into the joint and then performing an MRI.
58
MRI Contraindications
* Pacemakers
* Metal clips
* Metal valves
* Metal stints
* Slivers of metal embedded in the eye
* Cochlear implants Stents
59
Is Internal fixation a contraindication for MRI?
not a contraindication, although it is recommended that the **hardware be in at least 6 weeks**.
This gives it enough time for adequate bone incorporation
60
CAT scan
| (computed axial tomography)
* an x-ray that uses computed axial tomography to generate cross-sectional images
* CAT scans are **less expensive and quicker** than MRIs but have a **high radiation exposure**
* CAT scans are used in podiatry for **coalitions, complex fractures,** and **Charcot foot.**
61
Bone Scans
(scintigraphy) how it works
* good sensitivity and poor specificity
* Radioactive compounds (radiopharmaceuticals) are slowly injected into the patient and localized in specific organs.
* A scintillation probe or detector is positioned over the target, and emitted gamma photons are converted to visible light and counted.
62
what are “hot spots” and “cold spots” on bone scans?
* Hot spot: Area of high radiopharmaceutical uptake
* Cold spot: Area of low radiopharmaceutical uptake
63
Bone Scan
purpose
* Identifies areas of **increased bone turnover or osteoblastic activity** (i.e., fractures, bone tumors)
* allows **early diagnosis of a stress fracture (as early as 7 hours post-injury)**
64
Bone Scan:
podiatric indications
* Osteomyelitis
* trauma/inflammatory arthritis
* stress fracture
* tumors
* nonspecific pain
65
Technetium-99
(Tc-99m)
overview
* Highly selective for bone metabolism (osteoblastic activity)
* Normal uptake seen at tendon insertion, site of bone growth in children, epiphyseal plates, areas of constant stress, or osseous remodeling
* Will pick up in any areas of focal inflammation or bone turn over
* Used to identify fractures, tumors, infections
66
what **bone-imaging agents** can be combined with Technetium-99 in a bone scan?
* **Tc-99MDP** (methylene diphosphate)
* *assess capillary bed perfusion in DM pts*
* *assess healing potential in ischemic ulcers*
* **Tc-99MAA** (macroaggregated albumin)
* *identifies areas of increased bone metabolism (fractures) and increased blood flow*
* *normal uptake in tendon insertions, epiphyseal plates, and areas of constant stress/osseous remodeling*
* **Gallium-67 Citrate (Ga-67)**
* **Indium-111 (In-111)**
* **Thallium-201 (Ti-201)**
* **Combined Tc and Ga Bone Scan**
67
**Tc-99MAA**
(macroaggregated albumin)
chracteristics
* Images are obtained at **2 to 4** hours.
* **Osteoblastic-mediated chemo-absorption** onto the surface of hydroxyapatite crystals
* Half-life of 6 hours
* Useful 140-keV gamma photon
* **50% is excreted by the kidney; so adequate hydration/voiding is important to reduce the radiation exposure to bladder wall.**
68
4-Phase Bone Scan
| (Tc-99 **MDP**)
uses **methylene diphosphate** bone imaging agent
* 1st phase—radionuclide angiogram (blood flow phase)
* Images are taken 1 to 3 seconds apart immediately following injection.
* Shows dynamic visualization of blood flow
* Provides information about the relative blood supply to the extremity
* 2nd phase—blood pooling images
* *Images are taken 5 to 10 minutes following injection.*
* *Quantifies relative hyperemia or ischemia*
* 3rd phase—delayed image (bone-imaging phase)
* *Images are taken 3 to 4 hours following injection.*
* *Visualizes regional rates of bone metabolism*
* *determine cellulitis vs. osteomyelitis.*
* *By the 3rd phase with cellulitis, there should be a flushing and cleaning returning toward normal density. W*
* *ith osteomyelitis, Tc-99 will incorporate into the bone and show increased density.*
* 4th phase
* *Images are taken at 24 hours.*
* *Used in the diagnosis of osteomyelitis; at this phase, it shows greater bone activity and less soft tissue activity.*
69
How to use 4th phase bone scan to determine positive OM diagnosis
utilizes ratio of bone activity to soft tissue activity
* If the ratio (inc. bone activity) at 24 hours has increased more than one whole number compared with the 3rd phase, it is **positive for osteomyelitis.**
* If the ratio at 24 hours is decreased more than one whole number compared with the 3rd phase, it is negative for osteomyelitis.
* If the ratio at 24 hours is less than a whole number different compared with the 3rd phase, it is inconclusive.
70
Gallium-67 Citrate (Ga-67)
* binds to **WBC, plasma proteins, siderophores, and iron-binding proteins** (transferrin, ferritin, lactoferrin)
* Identifies neoplasms and inflammatory disorders
* Imaging is performed at 6 to 24 hours for infections
* Imaging is performed at 24 to 72 hours for tumors
* Excreted by the kidneys
* Half-life is 78 hours; thus, **radiation dose is high**
71
Indium-111 (In-111)
**More accurate at assessing infection if gallium studies are inconclusive**
* Binds to cytoplasmic components of the WBC membrane
* Spleen and liver light up because of WBC destruction at these locations
* Used for leukocyte-mediated pathology—inflammatory disorders Images are taken at 18 to 24 hours.
* More accurate at assessing acute infection, while Ga-67 is more sensitive for subacute and chronic infection
* Half-life is 67 hours.
* Rather than simply injecting the radiopharmaceutical, In-111 bone scans involve drawing blood from the patient, isolating WBCs, labeling them (with In-111), and then reintroducing them back into the bloodstream.
72
Thallium-201 (Ti-201)
used to assess foot perfusion
73
**Combined Tc and Ga Bone Scan**
* Combining technetium (bone- imaging radionuclide) and gallium (inflammatory-imaging nuclide) gives more information than either scan alone
* **Technetium should be given first,** because it has a shorter half-life, followed by gallium at 24 to 48 hours
* When referring to Tc as either (+) or (−), they are referring to phase 3 (bone-imaging phase)
* **Tc reveals if bone is involved, and Ga reveals if WBCs are involved**
74
FLUOROSCOPY
“C-arm”
* type of x-ray machine that allows real-time moving images.
* shape of a “C,” with the x-ray beam at one end and the image receptor at the other
* a mobile unit that can be easily manipulated in surgery to assess joint motion and internal fixation or to locate foreign bodies
75
DIAGNOSTIC ULTRASONOGRAPHY
* uses **sound waves** to visualize structures
* diagnostic US produces **no heat or tissue damage**
* most common podiatry **probe is a 7.5 mHz** and **can penetrate tissue up to 7 cm deep**
* Diagnostic US can be used in the presence of pacemakers and metallic implants
76
near field
| (Ultrasound terminology)
**Structures in the upper half of the monitor**
(Fresnel zone: adjacent to transducer face and has converging beam profile)
77
far field
| (ultrasound terminology)
**structures that appear in the bottom half of the monitor**
78
echogenic
| (ultrasound)
bright white image
* When the US wave encounters a **very dense** object, such as bone, the sound wave bounces back, allowing **very little sound wave to pass through the tissue**
79
Anechoic
| (ultrasound)
black image
* When the US wave passes through an object **without any echo**, the image is black
* Examples of this would be a fluid-filled cyst (ganglion cyst)
80
**_Hyper_**echoic
| (ultrasound)
Brighter echo showing up as white
* Examples of hyperechoic structures include:
* bone
* scar tissue
* tendon (hyperechoic relative to muscle)
* ligament, nerves (hyperechoic relative to muscle)
* ulcer sinus tract (relative to surrounding ulceration)
81
**_Hypo_**echoic
| (ultrasound)
Less echo showing up GRAY on monitor
Examples of hypoechoic structures include:
* fluid-filled cyst
* muscle
* ulcerations
* inflammation
* tendon tears
82
Plantar fasciitis
on ultrasound
Abnormal plantar fascia measures **greater than 4 mm thick** and **decreased echogenicity (darker)** indicative of inflammation.
*Normal plantar fascia is less than 4 mm in thickness, and hyperechoic with multiple parallel lines on longitudinal scan.*
83
Plantar fibromas
on ultrasound
Fusiform-shaped heterogeneous **hypoechoic mass (dark)** adjacent to the plantar surface of the plantar fascia
84
Morton Neuroma
on ultrasound
A discrete well-defined **round hypoechoic mass** (**dark**) just proximal to the metatarsal head in the interspace
85
Ganglion
on ultrasound
Presents as a **well-defined anechoic (black)** lesion
86
Tendinosis and Tendon Tears
on ultrasound
Present as **hypoechoic thickening (inflammation/ - dark)**;
**may also be hypoechoic area surrounding the tendon** indicative of fluid and inflammation
The torn fusiform portion of tendon is heterogeneous as compared with the rest of the tendon
87
Ultrasound-Guided Injections
During US-guided injections:
the **needles** will be **hyperechoic (bright)**
the bolus of **anesthetic or cortisone will appear as hypoechoic infiltration**
88
Diagnostic Ultrasound
Indications
* Plantar fasciitis, tears
* Muscle injury
* Capsulitis
* Heel spurs
* Morton neuroma
* Stress fractures
* Achilles injury
* Tendonitis/tendon tears
* Ligament tears
* Soft tissues masses (fibromas)
* Cysts/ganglions
* Bursitis
* Foreign bodies
* US-guided injections, aspirations, and biopsies
89
pigmented villonodular synovitis
90
exposure
defined by the measure of the amount of ionization that is PRODUCED when radiation passes through matter
91
dose equivalent
the measure of the biological damage caused by radiation
92
effective dose equivalent
the measure of biological damage caused by radiation to a **certain part of the body that is exposed**
93
absorbed dose
measure of the amount of energy that is ABSORBED in matter when radiation passes through it
94
intraosseous ganglion (IOG)
95
Bremsstrahlung radiation
when the negatively charged electrons approach the vicinity of a positively charged nucleus, the electron may deviate from its path
96
intraosseous lipoma
97
unicameral bone cyst
98
frieberg's infarction: avn of 2nd metatarsal head
thought to be associated w/ young women who wear high heels (w/ constraint of midfoot and forefoot)
99
what aspect of an image does kVp affect?
increasing kVp?
kVp controls the number of shades of gray
* ⇡ kVp → **⇣ contrast**
* ⇡ kVp → ⇣ mA → **lower patient dose**
100
how does mA affect image quality?
mA (exposure time) affects density and image quality
* when the film density is kept constant:
* the higher the kVp, the lower the resolution and image contrast percentage
* the higher the mAs, **the higher the resolution and image contrast percentage**
101
when comparing MRI and CT,
MRI is superior modality for what?
evaluation of:
* stress fractures
* infectious processes (such as OM)
* bone tumors
102
# define:
90-degree pulse
(flip angle)
the radiofrequency pulse in which motion from the z-axis to the xy-plane is geometrically a change of 90 degrees
once the energy is turned off, the protons begin to re-align with the z-axis
103
how does a radiofrequency pulse generate an MRI image?
Radio-frequency pulse changes the motion of protons from the z-axis to the xy-plane (90 degree change)
when RF is turned off → protons begin to realign w/ z-axis
process of changing/re-establishing the proton alignment also produces small bursts of radio-frequency energy, which are detected as small voltages by a receiver coil
the MR machine converts received voltage changes into digital data to ultimately produce final images
104
Law of Bergonie and Tribondeau
**states the radiosensitivity of a biological tissue is directly proportional to the mitotic activity,** and inversely proportional to the degree of differentiation of its cells
as such, Bone Marrow is most sensitive \> GI tract \> CNS
105
how does plaster, fiberglass, either wet or dry affect the mAs needed for an image?
plaster is denser than fiberglass
* Wet + Plaster → increase mAs x **3 times normal**
* Dry + Plaster → increase mAs x 2 times normal
* Wet + Fiberglass → increase **mAs x 60%**
* Dry + Fiberglass → increase mAs x 40%
106
radiographic findings:
Hyperparathyroidism
it's a disease characterized by INCREASED OSTEO**CLASTIC** activity due to elevated parathyroid hormone levels
the osteoclasts create areas of radiolucency/decreased density on xray
* resorption beneath the periosteum *(\*one of the earliest signs seen on x-ray)*
* *medial aspect of the shaft of the middle phalanges is usually affected*
* *loss of bone along shafts creates **smudges out or toothbrush bristle** appearance*
* bone loss at phalangeal distal tufts in the hands and feet (acroosteolysis)
107
what causes the metaphyses to be **frayed, irregular, with a paintbrush** appearance?
Rickets *(disease in children from abnormalities in calcium, phosphorus, or vitamin D metabolism)*
osteoid is produced but fails to mineralize
leads to widening of the physes and absence of the sclerotic zone of provisional calcification
frayed metaphyses are due to **disorganized spongy bone**
as growth and cell hypertrophy continues at the physes, the cells push/extend into the weakened metaphysis creating a **cupped appearance**
108
proton density
**number** of protons present in a given tissue **VOLUME**
**higher proton density → larger generated signal**
(therefore, protons in different tissues have different magnetic properties which dictate how they will react to the magnetic and radio frequency pulses)
109
what does a “chevron-shaped” peroneus brevis tendon indicate?
**longitudinal tear**
*axial images are important to evaluate tendon; high signal can be seen w/in tunnel*
110
magic-angle phenomenon
It is confined to regions of tightly bound collagen at **54.74°** from the main magnetic field (B0), and appears **hyperintense**, thus potentially being **mistaken** for [tendinopathy](https://radiopaedia.org/articles/tendon-pathology?lang=us)
111
a **fat-containing** lesion like a **_lipoma_** has a:
* short T1 signal
* long T2 signal
112
will osteomyelitis show **increased density** on WB xrays?
No, markedly increased density is not a radiographic feature of OM;
therefore it can be excluded from the differential dx
113
what factors are most important to minimize radiation dose to patient?
114
how are TE and TR
related to T1 and T2?
In clinical practice the **TE is always shorter than the TR** and usually it is lower than 30 msec.
The **TR is usually lower than 500 msec**.
TE and TR scan parameters can help determine if the image is T1-weighted or T2-weighted.
