radNotes

- diagnostic x-rays produced when energies of 20 to 150 keV are stopped in matter, resulting in EM radiation
- electronics going towards a positive anode gain kineitc energy of eV
- when kinetic energy of electrons hit the anode, x-rays and heat produced
- radiation, energy loss converted directly to a photon
- xrays generated by two different processes: 1) bremsstrahlung radiation 2) characteristic x-ray production

Bremsstrahling radiation
- “breaking x-rays” - electrons hit the nuclear electric fields and slow them down, changing their direction
- emission of photon
- bremsstrahlung x-rays produce continuous spectrum of radiation
- if electronic gets closer to nucleus, the greater interaction leading to higher energy of resulting x-ray
- this type of x-ray production increases w/ higher kV and higher Z of anode

Characteristic radiation
- when inner shell electrons of anode target are ejected by incident electrons
- in order to eject an electron from the anode, the incident electron must be high energy to overcome binding energy
- after striking anode, the void is filled by an outer shell electron which drops in, emitting energy which is called characteristic radiation… i.e.  K shell x-rays
- sometimes excess energy is released as an AUGER electron
- K shell energy levels are that relevant to diagnostic radiology

- conversion of AC to DC
- diodes accomplish this
- full wave, half wave
- single phase generators… used in dental units
- three phase generators obtain power from 3 lines of current
- high frequency generators are now used over three phase generators… convert AC into low voltage DC and then into high freq AC and into high voltage AC… goal is then to achieve constant waveform

1. Beta Minus decay
- neutron converted to proton, emitting a beta particle (energetic electron) and antineutrino

2.  Beta Plus decay
- proton converted to neutron, emitting a positron (positively charged electron) and a neutrino

3.  Electron Capture
- proton inside nculeus becomes neutron by capturing an electron from outer shell, emitting a neutrino
- occurs when there are too few neutrons and too many protons
- excess energy is emitted as a characteristic x-ray or  so called “AUGUR ELECTRON”… the energy of this aurger electron is equal to the characteristic x-ray energy less the electron binding energy

4.  Alpha Decay
- radionuclide emitting an alpha particle which is 2 neutrons and 2 protons (helium)
- Z > 82 unstable and releases alpha
- alpha particles have alot of energy… little risk as external radiation but pose a high risk if ingested/injected

- nuclides occur when there are different protons or neutrons
- unstable radionuclides are radioisotopes
- Atomic mass = protons + neutrons
- unstable nuclide becomes stable by alpha, beta, gamma decay
- SI unit of radioactivity / activity is BQ (becquerel) and non-SI unit is curie (Ci)
- one Bq is one transformation/second
- one Curie is 3.7 x 10^10 transformations/second
- one Curie = 37 kBq

- ramps up voltage and converts AC to DC
- controls voltage, current, and exposure time
- Power P = V x I (kilowatts)

- charged particles lose energy when passing through matter
- LET (linear energy transfer) measures loss of energy of a charged particle in thousands of eVs for each micrometer of distance traveled by the single particle
- 0.5 keV is the energy electrons/positrons lose when traveling through 1 um of soft tissue … these are “low LET” radiation
- alpha particles lose alot of energy, 100+keV.. “high LET radiation”
- energy from radiation causes DNA damage, transfers to heat (which is usually minimal)

“Lover’s Fracture”

- Results from axial load, jumps, hard falls
- Decreased Boehler’s angle (less than 20 degrees), normal is >20 but normal angle can be seen in fx
- 75% majority have intraarticular extension to subtalar joint
- 10% bilateral
- Think also other axial load injuries like vertebral burst fx (”DON JUAN FRACTURES” )
- Think Pilon fx of ankle
- Stress fx is more linear along posterior edge of calcaneus (runners, diabetics, and older individuals)

The tripod fracture, also called the zygomaticomaxillary complex or malar fracture, is composed of a set of fractures including the lateral orbital wall, inferior orbital floor, and the zygomatic arch.

Cause:

• direct blow to malar eminence

Clinical features:

• facial bruising/swelling
• flattened malar eminence
• loss of facial sensation below orbit (infraorbital nerve involvement)
• trismus / altered mastication
• diplopia +/- ophthalmoplegia

Fracture line:

• laterall wall of maxillary sinus
• orbital rim +/- infraorbital foramen
• orbital floor
• zygomatico-frontal suture / zygomatic arch

The appearance of intracranial hemorrhage at magnetic resonance (MR) imaging depends primarily on the age of the hematoma and the type of MR contrast (ie, Tl or T2 weighted). As a hematoma ages, the hemoglobin passes through several forms (oxyhemoglobin, deoxyhemoglobin, and methemoglobin) prior to red cell lysis and breakdown into ferritin and hemosiderin.

Five distinct stages of hemorrhage can be defined:

Baby Doo Doo Mnemonic

A mnemonic has been developed to help memorize the sequence of signal intensities.

“It Be Iddy Biddy Baby DooDoo”

This phrase can be broken into the following segments:

• It Be = I B
• Iddy = I D
• Biddy = B D
• Baby = B B
• DooDoo = D D

The letters from this phrase can then be lined up into a table that designates the anticipated T1 and T2 signal intensities for blood at each of the different stages.

- non-shadowing, non-mobile
- less than 7 or 8 mm
- multiple
- if >10 mm or broad based, ?mass/gallbladder carcinoma
- DDX: inflammatory polyps, adenoma, focal adenomyomatosis, gallbladder adenocarcinoma, metastases (melanoma)