Test 4 Rad Bio Review

Tube Housingo Protect for off focus, leakage radiation, and restricts primary beamo 100mR/Hr at 1 meter from the source at its highest voltage

Control Panelo Located behind protective secondary barrier.o Must indicate when tube is energized. Tone is usually emitted

SIDo Must have an indicator of distance o Indicator must be within 2% of the indicated SID.

Collimatorso Light Localizing Variable-aperture rectangular collimator - modern equipment

2 sets of adjustable lead shutters Reduce off focus radiation

light source mirror

o Aperture diaphragms. Cones. Cylinderso Confine useful or primary beam. o Reduce scatter radiation, and pt dose o Pt Skin surface should be at least 15 cm below the collimator 1in=2.5cm o Beam and Light must be aligned within 2% of SID o PBL-Positive Beam Limitation

Collimators are automatically adjusted Must be within 2% of SID

Filtrationo Removes low energy photons from beamo Increases mean energy or quality of beamo Called Hardening of Beam o Decreases overall intensityo Absorbed dose to pt is decreasedo Inherent-

.5mm AL equivalent Collimator- 1mm AL equivalent

o Added-usually sheets of ALo Total= Inherent + Added

2.5mm AL equivalent for above 70 kVp o For Mammo

Molybdenum uses either Molybdenum or rhodium filter Rhodium only uses Rhodium

o HVL – required to decrease the intensity of primary beam by 50% of its value

Measured Beam Quality Exposure reproducibility

o Tube can duplicate exposures for any given combinations of kVp, mA, and time Be within 5% or less is acceptable

Exposure Linearityo When settings are changed from on mA station to Another

Be within 10% of less is acceptable Screen Film Combo

o Rare Earth Screens Convert energy to light more efficiently Less stress on tube Can produce Quantum Mottle

o Lowers pt dose Selection of kVp & Screen film combo are most important in considerations of pt

dose Grids

o Improve Contrast and Visibility of detailo Greater than 10cm or 70kVpo Pt dose increase with a grid

Doseo SSD-Source-Skin Distance

Must be at least 12in CR/DR

o Dose Creep-practice of overexposing pts to avoid repeats due to exposure technique Fluoroscopy

o produce greatest pt dose o Benefits of Intesification

Increased image brightness Saving of time for radiologist Pt dose reduction

o Requires less mA Between1-5 mA Before 3-5 Now 1.5-2

o 75 to 110 kVp for adult pts. o Children decrease peak kVp by as much as 25% o 2.5mm Al equivalento SSD no less than 15 in for stationary, 12 in for mobileo Timer- for every 5 min of fluro o Entrance Skin Exposure

A max of 10R per minute

o Primary Protective Barrier 2mm lead equivalent for intensifier unit

Mobile Fluroo Source to end of collimator distance of 12in.

Digital Fluoroscopyo Pulsed Progressive Systems for Dose Reduction

X-ray beam is off while image is being scanned , decrease pt dose High Level Control Procedures

o Invasive procedures by a physician with aid of fluroo Exposure rates are highero For visualization of smaller and lower contrast objects o Constant Audible Signal o FDA recommends a notation in pt chart if Skin dose is in rage or 1 to 2 Gy

Chapter 11 Gonadal Shielding

o Used when reproductive organs are within 5cm or properly collimated beamo First Step is always Adequate Collimation of AOI o Female Pts- flat shield reduces exposure by 50%

1in medial to ASIS place shieldo Male pts- flat shield reduces by 90-95%

Over pubis symphysis o Types of Shields

Flat Contact Shadow

Suspended above the pt. Shaped Contact

Contour to enclose male reproductive organs Not recommended for PA

Clear Lead Impregnated 30% lead by weight

Technical Exposure Factors o Minimal pt dose, penetration of area, adequate density and contrast. o High kVp low mAs .

Processing o Quality control program

Monitoring and maintenance of processing equipment Air Gap Technique

o Removes scatter by using increase OID o About same as an 8:1 Grid

Repeat Image

o Image that must be performed more than once . o Double Doseo Repeat Analysis program

Increase awareness among staff to produce optimal x-rays Techs become more careful Identifies concerns and problems

Ways to Measure Radiation Received by Pto 1.entrance skin exposure

May be converted to Skin Doseo 2.Skin Dose

TLDs most often used Responds similar to human tissue In Fluro take exposure at table times the fluro time

o 3. Gonadal Doseo 4. Bone Marrow Dose

Genetically Significant Dose o Consequences of substantial absorbed dose of gonadal radiation become significantly

less when averaged over an entire population rather than just a few memberso For U.S. .20 mSV (20mrem)

Bone Marrow Doseo Average radiation dose to the entire active bone marrowo Usually less for children

Pregnant Pto Shield in reproductive organs 5 cm from edge of field o ICRP 10 day rule

Mammographyo Yearly mammo of women age 50 yearso Young tissue is more dense o Every other year age 40-49 years o Limit number of projections taken for dose reductions

CTo Skin dose for adjacent scans is greater than the dose for single scano Dose Distribution not same as diagnostico 30 to 50 mGy for head imaging o 20 to 40 mGy for Body imagingo Direct pt shielding not normally used

Pediatricso Smaller doses usedo Short exposures with high mA o More collimation used

o Projection orientation important. PA preferred

Chapter 12 Effective Dose Limits

o 5 rem(50mSv) –annual occupational Doseo Age in years X 1 rem = cumulative effective doseo .1 rem for continuous exposures= Public Exposure o .5 rem for infrequent exposures= Public Exposure o Extra Amt of Radiation absorbed by workforce does not significantly increase GSD

Dose Reductiono Pt source of scattero Stand at 90 degree angle to primary beam at a distance of 1m o Scatter 1/1000 intensity of primary beam

Protection pregnant workerso Make declaration in writingo Receive an additional monitor worn at waist level o Montly EqD .05 Rem o Maternity aprons .5mm lead equivalent , extra 1 mm lead transversely

Principals or Radiation o Time, Distance, Shielding o Distance most effective means of protectiono Inverse Square Law o Effectiveness of shielding materials depends on atomic number, density, and thickness

Primary Protective Barrierso Located perpendicular to undeflected line of travel of beam o 1/16in lead 7 feet upward from the floor

Secondary Protective Barriero Overlap primary by about ½ in o 1/32in lead. o Clear lead plastic impregnated with 30% lead by weight ,shatter resistant, .3 to 2 mm

lead equivalency Control booth Barrier

o Extend 7 feet upward from floor and permanently secured o Window consists of 1.5mm lead equivalent

Lead Aprons and Gloveso At least .25 mm lead o .5mm lead most used and recommended. o Thyroid minimum of .5 mm lead equivalent

o Protective Eyeglasses minimum ..35mm lead equiv. Personnel Protection during fluro

o .5mm lead must be worn o .25mm lead gloves o Spot Film Curtain

.25mm lead minimumo Bucky Slot Cover

.25mm lead minimum Doors to Room

o 1/32 inch of lead o Should always be closed during exposure

Radiation Shielding Categorieso Primary radiation-direct from x-ray tube o Scatter radiation-Compton interactions o Leakage radiation-penetrates tube housing

Workloado Weekly radiation use of x-ray roomo mAs per week or mA per min

Use Factoro Portion of beam-on time that x-ray beam is directed at primary barrier during the week

Occupancy Factoro Used to modify the shielding requirement for a barrier due to workload and space

beyond barrier is occupied Controlled area

o Adjacent to wall of x-ray room and used by occupationally exposed personnel Uncontrolled Area

o Are frequented by general public Caution Signs

o Radiation area, high radiation area, very high radiation area,o Symbol colored magenta purple, or black on yellow background.

Chapter 13 o Isotopes – atoms that have the same number of protons within the nucleus but have

different number of neutronso Isotopes that have an unstable arrangement of protons and neutrons are called

radioisotopes o Most common used radioisotopeo Tc99mo GM Counter o Used to detect radioactivityo Units of measurement for radioactivityo Curie – Traditional

o Becquerel – SI Dose Rate

o Rate=Exposure/Time