Safety Code 35 Flashcards
does safety code 35 apply to denstistry, chiro, podiatry, mammo?
no
they have other safety codes for those
somatic effects vs genetic effects
somatic= changes in exposed individual genetic= gives rise to genetic effects
how are estimates of incidence of cancer at low dose determined?
- cannot b measured
- based on linear extrapolation from relatively high doses
linear no treshold hypothesis
health risk from exposure is proportional to dose
4 main aspects of radiation protection for diagnostics
- jutification for medical exam
- patient is protected from excess radiation
- staff are protected
- general public is protected
who is ultimately responsible for safety of facility?
owner
when does responsible personel investigate exposures received by personnel?
- if exposure is higher that usual dose received by that person
- > 1/20 of dose limit for radiation workers
when must staff wear personal dosimeter
-if they are likely to receive a dose in excess of 1/20 of dose limit for radiation worker (i.e. 1 mSv) (i.e. occupationally exposed person)
o CNSC Radiation Protection Regulations says that personnel dosimetry is required for NEWs who have a reasonable probability of receiving an effective dose greater than 5 mSv in a one-year dosimetry period
HL7
health level 7
standard for exchanging information between medical information systems.
DICOM
digital imaging and communications in medicine
general requirements for diagnostics
- x-ray room cannot be used for more than one radiological investigation simultaneously
- unless essential, everyone leaves room when irradiation comes on
- personnel should keep away from x-ray beam
- irradiating someone for traning or evaluation is not allowed
- all personnel must use available protective devices
- workers who are likely to receive > 1/20 of dose limit must be declare radiation workers and wear personal dosimeter
- personal dosimeters must be worn and stored according to recommendations of dosimetry service provider. When a protective apron is worn, personal dosimeter must be worn under the apron. If extremeties likely to be exposed, additional dosimeters should be worn at those locations
- personal dosimetry records must be maintained for lifetime of facility
- female operator must notify employer of pregnancy
- if weak persons need support, holding devices should be used (not staff)
- all entrance doors to xray room should be closed while patient in the room and during exposure
- energized xray machines must not be left unattended
rules regarding mobile x-rays
- only use if needed
- direct xray away from occuppied areas
- operator must not stand in front of direct beam and must be > 3 m away from x-ray tube unless wearing PPE or behind leaded shield
- residual charge must be fully discharged before unit is unattended
requirements of radioscopy
-all persons with possible exception of patient must wear leded apron (shields and curtains are not enough)
one of greatest sources of exposure to personnel in radiology
angiography
requires the presence of a considerable number of personnel close to the patient, radioscopy for extended periods of time and multiple radiographic exposures
recommendations for angiography
- use [protective devices such as shielded drapes etc
- The patient is the largest source of scatter radiation. To avoid this scatter, operate the equipment with the tube under the patient and, if the tube is horizontal, stand on the side of the image receptor.
- PPE (including glasses) and dosimeters must be worn
- personnel not required right by patient should stand behind shields
largest source of scatter radiation in angiography
patient
medical and dental x-rays account for what % of man-made dose to public?
90%
when is risk of pregnancy small? (for pelvic tests)
10 days following menstruation
recommendations for pregnant or potentially pregnant women
Only essential investigations should be taken in the case of pregnant or suspected pregnant women.
When radiological examinations of the pelvic area or abdomen are required, the exposure must be kept to the absolute minimum necessary and full use must be made of gonadal shielding and other protective shielding if the clinical objectives of the examination will not be compromised.
If a radiological examination of the foetus is required, the prone position should be used. This has the effect of shielding the foetus from the softer X-rays and hence reducing the foetal dose.
Radiography of the chest, extremities, etc., of a pregnant woman, for valid clinical reasons, should only be carried out using a well-collimated X-ray beam and with proper regard for shielding of the abdominal area.
xray beam size limit
size of image receptor or smaller
considerations to ensure patient exposure is kept to minimum
- use of an anti-scatter grid or air gap between the patient and the image receptor;
- use of the optimum focal spot-to-image receptor distance appropriate to the examination;
- use of the highest X-ray tube voltage which produces images of good quality;
- use of automatic exposure control devices designed to keep all irradiations and repeat irradiations to a minimum.
what should you do before taking long series of images?
check the first one to ensure correct setup
difference between radioscopy and radiography
radiography is an off-line, static examination technique, while radioscopy is a dynamic examination technique with the potential for on-line examination and process control.
radioscopy is more dose- only use when necessary
why does operator monitor tube current and voltage when using AEC?
both can rise to high values without the knowledge of the operator, particularly if the gain of the intensifier is decreased
when should cinefluorography be used?
- when absolutely needed
- produces the highest patient doses in diagnostic radiography because the X-ray tube voltage and current used are generally higher than those used in radioscopy
recommendations for angiography
- shield eyes and thyroid if possible
- minimize irradiation time
- use more tube filtration (reduce low E xrays)
- use lower time frequency in pulse radiography
- produces the highest patient doses in diagnostic radiography because the X-ray tube voltage and current used are generally higher than those used in radioscopy
- in children and small adults, removing grid will reduce dose
- magnification may increase dose to patient
- use automated injection if possible
- if procedure is long, reposition tube so that same area of skin is not exposed to xray beam
- for each interventional procedure, document images, radioscopy time, air kerma rates, and resulting skin doses
what ia angiography
Angiography is a type of X-ray used to check blood vessels.
Blood vessels do not show clearly on a normal X-ray, so a special dye needs to be injected into your blood first. This highlights your blood vessels, allowing your doctor to see any problems. The X-ray images created during angiography are called angiograms.
reducing dose in CT
-reduce number of slices and overlap b/w adjacent scans as much as possible given quality required
where does radiation have most impact
reproductive cells and rapidly dividing cells
factors for reducing dose to sensitive tissues
- correct collimation of x-ray beam
- examine kids and adolescents really if only necessary..
- use gonads shields if clinical objectives not compromised, patient is of reproductive age, gonads aer within or near beam
- use proper technique
- maintain sensitivity of imaging system
what technique reduces dose in radioscopy?
use of higher tube voltage and filtration and lower tube current will almost always reduce the gonad dose
diagnostic reference levels
for typical procedures, the difference in radiation doses can be as wide as a factor of 50 to 100
- reference levels to help optimize techniques, rather than max dose limits
- better control of patient exposure to x-rays
- AVERAGE of population should meet thiese targets, not necessarily each patient
what are DRLs based on?
CTDIw
- at least 10 patients for sample size, ~ 70 kg
- preferable to use phantoms
-measure entrance dose with TLDs, dose-area-product meters
entrance surface dose chest (PA)
0.2-0.3 mGy
entrance surface dose chest (LAT)
0.7-1.5 mGy
entrance surface dose thoracic spine (AP)
5-8 mGy
entrance surface dose thoracic spine (LAT)
7-10 mGy
entrance surface dose lumbar spine (AP)
7-10 mGy
entrance surface dose lumbar spine (LAT)
15–30 mGy
entrance surface dose abdomen (AP)
7-15 mGy
entrance surface dose pelvis (AP)
5-10 mGy
entrance surface dose skull (AP)
4-5 mGy
entrance surface dose skull (LAT)
2-3 mGy
dose-area-product for abdominal radioscopy
20-70 Gycm2
dose-area-product for coronary angio
35-75 Gycm2
dose-area-product for barium enema
30-60 Gycm2
CTDIw and dose-length product for head CT
60 mGy
930-1300 mGycm
CTDIw and dose-length product for face and sinuses
35 mGy
360 mGycm
CTDIw and dose-length product for chest
30 mGy
580-650 mGycm
CTDIw and dose-length profuct for abdo-pelvis
35 mGy
560-1100 mGycm
CTDIw and dose-length product for liver and spleen
35 mGy
470-920 mGycm
3 considerations for designing and planning an x-ray facility
- prepare facility plans
- consider room design and layout
- determine parameters governing shielding requirements
weekly dose limit for operator for diagnostics
0.4 mSv/week
where should control booth be located?
whenever possible, such that the radiation has to be scattered at least twice before entering the booth
typical workloads for xray facilities
cardiac angio- 4800 mA min/wk other vascular angio- 2000 mAmin/wk chest radiography - 100 mAmin/wk other radiography- 320 mAmin/wk radioscopic- 400 mAmin/wk
use factor for ceiling for diagnostic x-ray
1/16
not routinely exposed to direct radiation beam
assumptions in NCRP 147 for shielding calcs
- The attenuation of the radiation beam by the patient is neglected.
- The incidence of the radiation beam is always perpendicular to the barrier being evaluated.
- The calculation does not take into account the presence of materials in the path of the radiation other than the specified shielding material.
- The leakage radiation from the X-ray equipment is assumed to be an air kerma of 0.876 mGy h-1.
- The minimum distance to the occupied area from a shielded wall is assumed to be 0.3 m.
storage for radiographic film
< 0.1 mG over stored period of film
-Once films are loaded into cassettes, radiation exposure levels should be less than 0.5 µGy and the resulting increase in the base-plus-fog should be less than 0.05 O.D
control booth is secondary or primary barrier?
shpuld be secondary as xray should never be directed to control booth
primary barrier walls for radiography equipment
wall behind the vertical image receptor, or “wall or chest bucky”, and the floor under the radiographic table. For dedicated chest radiographic equipment, the wall behind the image receptor is considered a primary barrier.
barrier types for radioscopic x-ray
only secondary
but typically radiographic is also in the room and need to shield for that
shielding for CT
only secondary
doesn;t rely on W
use NCRP 147
what regulations must all new, used, and refurbished medical x-ray equioment and accessories abide by?
Radiation emitting devices act
Food and Drugs Act
outline of process for equipment purchasing
- do needs analysis
- decide on equipment specs
- analysis of vendor quotation and purchase contract
- acceptance testing
what is included in acceptance testing
- components are what was ordered
- system mechanical integrity and stability
- verification of electrical installation
- verification of x-ray performance
- verification of imaging or diagnostic performance
-results from acceptance testing are used to assign baseline values
x-ray tube shielding requirement
- 1 mGy/h at 1 m away from focal spot when operated at max energy input in 1 hour
- 20 uGy/h at 5 cm from any accessible surface when equipment is not in loading state
x-ray beam filtration requirements
There must be radiation-absorbing filters that provide a degree of attenuation such that the first Half-Value Layer (HVL) of aluminum is not less than the values shown in Table 8 for a selected X-ray tube voltage
- 5 mm for 70 kV
- 3 mm for 120 kV
coefficient of variation
ratio of standard deviation to mean value
radiographic equipment requirements
- coefficient of variation for 10 consecutive measurements < 0.05
- radiation output linearity: |X1-X2| = 0.1 (X1+X2)
- irradiation switch
- Automatic Exposure Control–For film-based systems, the automatic exposure control device shall perform in such a way that the variation of optical density in the resultant radiograms shall not exceed the value of
0. 15 when the X-ray tube voltage is variable and the thickness of the irradiated object is constant,
0. 20 when the thickness of the irradiated object is variable and the X-ray tube voltage is constant,
0. 20 when the thickness of the irradiated object and the X-ray tube voltage are both variable, and
0. 10 when the thickness of the irradiated object and the X-ray tube voltage are both constant. - For digital systems, the performance of the automatic exposure control must be assessed according to the manufacturer’s procedures and must be within the manufacturer’s specifications. It is recommended that the automatic exposure control should perform in such a way that the variation in the mean linearized data on a constant region of interest does not exceed 20% for constant X-ray tube voltage and constant thickness of the irradiated object, when the X-ray system is operated in conditions representative of the typical clinical use
- current-time-product limit- if > 50 kV, current-time product cannot exceed 600 mAs
-Accuracy of Loading Factors--The loading factors must not deviate from the selected value, for any combination of loading factors, by more than 10% for X-ray tube voltage, 20% for X-ray tube current, 10% + 1 ms for loading time, and 10% + 0.2 mAs for current-time product.
- AEC must have min irradiation time of 1/60 s or time required to deliver 5 mAs
- min field size must not be greater > 5x5 cm at 100 cm focal spot to image recepter
- must have radiation field and light field alignment
- must have focal spot marked on housing n
radioscopic equipment regulations
-loading factors must not deviate by more than 10% for tube voltage, 20% for tube current
-visual indicators for voltage and current
-image intensifier has protective shield and cannot emit radiation unless protective shield is on
-focal spot distance must not be less than 30 cm for mobile, 38 cm for stationary, 20 cm for specialized. distance for 50mGy/min for small format equipment
-irradiation switch
-chronometer- indicates time equipment has been emitting xrays
-High-level Irradiation Control–High-level irradiation control must be activated by a separate means that requires continuous pressure by the operator to emit X-rays
-Maximum Air Kerma Rates–The following maximum air kerma rates apply to radioscopic equipment except during recording of radioscopic images:
50 mGy/min for equipment not equipped with an automatic intensity control;
100 mGy/min for equipment equipped with an automatic intensity control; and
150 mGy/min for equipment equipped with both an automatic intensity control and a high-level irradiation control and the high-level irradiation control is activated.
-transmitted/scatter radiation from imaging assembly cannot exceed air kerma rate of 2 mGy/h for entrance air kerma rate of 1 Gy/min
-must have last image hold system
what does irradiation switch require?
continuous pressure by operator for entirety of exposure
general xray equipment requirements
-warning signs, markings, mechanical stability, indicator lights
-indication of loading factors
-Irradiation Control–There must be an irradiation switch, controlling timer or other mechanism to initiate and terminate X-ray production.
-Controlling Timer–When the equipment is equipped with a controlling timer it must be constructed so that
it can automatically terminate an irradiation on completion of a preset irradiation time, on attainment of a preset current time product value, or on completion of a preset number of X-ray pulses,
it permits the operator to terminate an irradiation at any time,
it automatically resets itself to its original setting or to zero on termination of an irradiation, and
when it is at zero, at the off position or at an unmarked setting, an irradiation cannot occur.
-appropriate xray tube shielding
-appropriate xray beam filtration
CT equipment requirements
- irradiation control
- visual indications
- emergensy stop near gantry
- min focal spot to skin distance of 15 cm
- min HVLs of Al are given in a table
2. 1 mm for 70 kV and 3.8 mm for 120 kV - preview image- reference lines must not differ from true position by more than 2 mm
- light field - coincidence within 2 mm
- couch position must be within 1 mm of indication
- recorded data must be accurate- patient orientation
CTDI100
required for CT
–50 mm to 50 mm, divided by number of sections X thickness
at what locations must CTDI 100 be provided?
- axis of roratio of phantom
- at 0, 90, 180, 270 degrees at 1 cm interior to phantom
CT required info
- CT conditions of operation
- dose info for head/image in terms of CTDI100- has to encompass range of operations that can be done on CT
- dose profile in centre location of dosimetry phantom
- noise
- contrast scale
- MTF
- thickness at centre of imaging section
- sensitivity profile at center of imaged section
- CTDIw
- DLP
contrast scale
(ux-uwater)/(CTx-CTwater)
about 2 X 10^-4 /cm HU
CTDIw
1/3 CTDI100 (center) + 2/3CTDI100(peripheral)
DLP
dose length product
DLP = CTDIw X slice thickness X number of slices in sequence
max OD from bas material and film fog
0.3
PACS
pictures archiving and communication system
what is teleradiology
electronic transmission of radiological images from one location to another for the purposes of interpretation and/or consultation
protective lead apron requirements for different xray kV
- 0.25 mm for 100 kV or less
0. 35 mm for 100150 kV
protective equipment recommended for interventional procedures
- full wrap-aroud Pb gowns with 0.5 mm in front and 0.25 mm in back
- thyroid shields with 0.5 mm Pb
- leaded glasses if scatter to eyes is approaching limit
protective gonad shields for patients
> 0.25 mm Pb
0.5 mm for 150 kVp
protective gloves Pv thickness
0.25 mm
how often is protective equipment tested for integrity?
yearly
Pb thickness of ceiling mounted acrylic screens and moveable shields
0.5 mm Pb
after you make changes to xray facility (barriers, equipment modification), do you survey it?
yes
why do we do periodic surveys?
- detect problems due to equipment failure, or long term trends
- frequency depends on type of facility
considerations for disposal of xray equipment
-assess if hazardous materials (ex. polychlorinated biphenyls), and Pb may be in xray tube housing
3 aspects of QA
diagnostic information quality
clinical efficiency
patient dose
4 steps included in establishing QA procedures
- make sure equipment is operating properly
- assess the baseline performance
- use a reference test image to evluate image quality
- determine action levels- acceptable vs unacceptable results
components checked during acceptance testing
- verify delivered components or systems are as ordered
- system mechanical integrity and stability
- verify electrical installation
- verify xray performance
- verify imaging or diagnostic performance
how often is film processor function evaluated?
every morning
-includes sensitometric strip processing
pass criteria for sensitometric strip processing
- base plus fog within 0.05 of operating level
- mid densit within 0.15 of operating level
- density different within 0.15 of operating level
daily QA tests
- warm up equipment
- check meters are working
- do visual inspection of equipment and make sure it moves properly
- ensure darkroom is clean
- check film processor function
- overall visual assessment of electronic display devices (view test patterm 30 cm from display)
weekly QA tests
- visual inspection of cleanliness of imaging systems
- viewboxes condition
- laser film printer operation (use test patterns)
- CT number accuracy
- CT noise
- CT uniformity
- DSA performance
criteria for laser film printer operation test pattern to pass
the 5% patch must be just visible inside of the 0% patch,
the 95% patch must be just visible inside the 100% patch,
no geometrical distortion upon visual inspection,
no artifacts upon visual inspection.
the patches are literally squares of different contrast within larger square
criteria for CT number test to pass
CT number of water must be 0 +/- 4 HU
criteria for CT noise to pass
cannot deviate from baseline more than +/- 10% or 2 HU
-The established baseline noise levels in a CT system should not deviate from the manufacturer specified noise value by more than ± 15%
should CT quality tests (ex. noise, CT #) be for both axial head scan and axial body scan?
yes
diameter of ROI for noise test
40% of diameter of uniform phantom image
equation for CT uniformity
CT number in center of image - CT number at periphery
- use 4 peripheral ROIs
- diameter of each ROI should be 10% of phantom diameter
pass criteria for CT uniformity
within 2 HU of baseline
baseline must be within 5 HU
how to assess DSA performance?
use phantom with image quality test objects
monthly QA tests
- cassette, screen, and imaging plate cleaning
- darkroom temp and humidity (18-23 C, 40-60%)
- darkroom light conditions
- film processor operation
- retake analysis (look at records of exams that were retaked- look for trends or repeated errors)
- electronic display device performance
- laser film printer operation (includes checking OD of various patches)
- CT tomographis section thickness
- calibrate CT number
- CT number linearity
film processor temperature display should be accurate to what?
0.5 C
what should retake rate be?
<5 %, not including QA films
test patterns you can use to test electronic device performance ?
SMPTE
TG18
max geometric distortions fro laser film printer operation monthly test
+/- 1 mm
how do you measure CT slice thickness
test device with ramps at angle to scan plane
- for thickness > 2 mm, pass criteria is within 1 mm from baseline
- for thickness 1 mm < t < 2 mm, pass criteria is within 50% of baseline
- for thickness < 1 mm, pass criteria is within 0.5 mm of baseline
how to measure CT slice thickness for helical scanning?
- thin disk or bead
- fwhm of senstivity profile as function of z position is slice thickness
how to do calibration of CT # (monthly)
pick same 2-3 cm2 area for water and air
CT number for water should 0+/- 4 HU and for air should be -1000+/-10 HU
how to measure CT linearity
- scan phantom with many known materials
- compare CT numbers to those baseline
- criteria for pass is set by manufactuer
what does SMPTE stand for?
society of motion picture and television engineers
is safety code 35 recommendation or reg?
recommendation
another word for radioscopy
fluoroscopy!
constraint level for pediatric ward
0.3 mSv/yr
x-ray tube shielding must be such that leakage radiation from xray source does not exceed ___ air kerma rate of
1 mGy/h at 1 m from focal spot
quaterly QA tests
collmator operation interlocks table angulation and motion compression devices operation chronometer operation (keeps time) protective devices (for fluoro)- ie 0.25 mm Pb drape, Pb drape should also be affixed under table to image intensifier - shield covering cassette holder (for under table fluoro) should be 0.5 mm Pb park position interrupt CT patient support movement CT spatial resolution CT low contrast detectability
descrie collimator operator test
ensure they move smoothly
can you turn on fluoro if entire beam is not recepted by image receptor?
No, an interlock should stop this
what is park position interrupt test?
When the image receptor is in the parked position, it should not be possible to energize the X-ray tube. This many be checked while wearing a lead apron and depressing the radioscopic irradiation switch to see if the system is activated.
how to measure CT spatial resolution for quaterly test?
The recommended method of measuring the spatial resolution is using the modulation transfer function curve, obtained from the Fourier transform of the point-spread function. The test device is a high contrast wire, typically 2 mm in diameter or less, placed in a tube of minimally attenuating material. The measurement of the 50% point and the 10% point of the MTF curve must be within 0.5 lp/cm or ± 15% of the established baseline value, whichever is greater.
- bar pattern- whould be 5 lp/cm or more
- pattern of holes or lines- resolution must be = 1 mm
CT low contrast phantom- how low should contrast of circles be compared to background?
< 1 % or 10 HU
semi-annual QA tests
CT laser light accuracy- 2mm for axial, 5 mm for isocentre alignment and sagittal and coronal scan localization lights
CT accuracy of automatic positioning of tonographic plane (using scanned projection radiograph)- within 2mm
CT accuracy of gantry tilt- within 3 degrees, test 0 tilt and each extreme angle
CT patient dose - CTDI100 for head and body - CTDIw must be within 20%
annual QA tests
- safelight (for film)
- film/screen contrast
- accuracy of loading factors
- radiation output reproducibility
- radiation output linearity
- xray beam filtration
- AEC
- x-ray and light field alignment
- xray beam collimation
- grid performance
- response function (CR/DR)
- exposure index
- dynamic range
- noise, uniformity, and image artifacts
- spatial resolution
- contrast detectability
- digital detector residual images (CR/DR)
- phantom dose measurements- entrance skin air kerma must be within limits
- typical image intensifier air kerma rate (fluoro)
- maximum image intensifier air kerma rate (fluoro)
- automatic intensity control (fluoro)
- image lag
- CT # dependence on phantom position
- CT radiation dose profile
- CT radiation dose-scout localisation image
- viewboxes
- electronic display device performance
- intengrity of protective equipment
- general preventative maintainance
describe safelight test
A film strip exposed to an optical density of 1.2 units must not show an increase in optical density greater than 0.05 units in two minutes exposure to the darkroom light environment.
describe accuracy of loading factors- accuracy required
For any combination of loading factors, the X-ray tube voltage must not deviate from the selected value, by more than 10%, the loading time must not deviate from the selected value by more than (10% + 1 ms), the X-ray tube current, must not deviate from the selected by more than 20%, and the current-time product must not deviate from the selected value by more than (10% + 0.2 mAs)
radiation output reproducility test
For any combination of operating loading parameters, the coefficient of variation of any ten consecutive irradiation measurements, taken at the same source to detector distance within a time period of one hour, is no greater than 0.05, and each of the ten irradiation measurements is within 15% of the mean value of the ten measurements
radiation output linearity requirement
|X2-X1| 0.1(X1+X2)
- if discrete, then X1 and X2 are two consecutive settings
- if continuous, then X1 and X2 are settings that differ by < 2
AEC QA requirements
For film-based systems, the automatic exposure control must be evaluated to ensure it performs in such a way that the variation in optical density in the resultant radiograms does not exceed the value of
- 15 when the X-ray tube voltage is variable and the thickness of the irradiated object is constant,
- 20 when the thickness of the irradiated object is variable and the X-ray tube voltage is constant,
- 20 when the thickness of the irradiated object and the X-ray tube voltage are both variable, and
- 10 when the thickness of the irradiated object and the X-ray tube voltage are both constant.
for digital systems- 20% within manufacturer’s specs
xray beam collimnation QA requirements
An evaluation of the beam limiting device must be made to ensure that the equipment is capable of aligning the centre of the X-ray field with the centre of the image reception area to within 2% of the focal spot to image receptor distance.
Radiographic X-ray equipment that has a positive beam limiting system must prevent the emission of X-rays until the beam limiting device is adjusted so that
the dimensions of the X-ray field do not exceed those of the image reception area, or the selected portion of that area, by more than 3% of the focal spot to image receptor distance, and
the sum of the absolute values of the differences in the dimensions of the X-ray field and the image reception area, or the selected portion of that area, does not exceed 4% of the focal spot to image receptor distance.
fluoro beam collimation QA requirements
the dimensions of the X-ray field differ from the corresponding dimensions of the image reception area by a distance that does not exceed 3% of the focal spot to image receptor distance, and
the sum of the absolute values of the differences in the dimensions between the X-ray field size and the image reception area does not exceed 4% of the focal spot to image receptor distance.
what is exposure index?
- indicates relative speed and sensitivity of digital receptor to incident xrays
- measures amount of xray photons that actually reach image receptor in relative image region
dynamic range QA requirements
For film screen systems, a high purity step wedge should be used to monitor the performance of the X-ray generator. When using a 11-step wedge, the acceptable variation in film density should be ± 1 step from the established baseline density, or when using a 21-step wedge, the acceptable variation in film density should be ± 2 steps from the established baseline density. For digital systems, the dynamic range is a measure of the maximum difference in attenuation that the system can simultaneously image, without loss of information due to saturation of pixels. A test object consisting of an attenuating plate terminated with a step wedge of 12 steps should be used. The number of non saturated steps or the thickness of the smallest non saturated step should be within established limits.
max air kerma rate of fluoro equipment- max mGy/min allowed
50 mGy/min when the equipment is not fitted with an automatic intensity control,
100 mGy/min when the equipment is fitted with an automatic intensity control, and
150 mGy/min when the equipment is fitted with both an automatic intensity control and a high-level irradiation control when the latter is activated.
how do you test automatic intensity control for fluoro?
The automatic intensity control system is designed to maintain the rate of the X-ray exposure to the image intensifier with changes in thickness and composition of the anatomical region being imaged. Place a dosimeter between a homogenous phantom and the X-ray source. Double the phantom thickness and repeat the exposure. The exposure measurement should be approximately double the first measurement.
CT number dependence on phantom position- QA requirement
water CT number within 5 HU when position of water phantom is varied over clinically relevant positions
CT radiation dose profile QA test
- ensure collimation of radiation beam does not exceed the prescribed scan width
- scan width is FWHM of radiation dose profile
- measure from density profile or film or compute from digital image
CT Radiation Dose-Scan Projection Radiograph/Scout Localization Image- QA requirements
The dose delivered from a scout localization image, which is a scanned projection radiograph, must remain within ± 20% of the nominal value. Changes in this dose can be indicative of problems with collimation or patient support movement
viewbox QA requirements
- luminence should be at least 2500 cd/m2
- light output should be uniform within 10%
- light output homogeneity within a bank of viewboxes should be within 20% of mean
- ambient light in reading room < 50 lux
electronic display device performance- what to use as test pattern?
SMPTE
TG18
max total defective area allowed for Pb aprons
670 mm2
Personnel protective equipment having a defect in the vicinity of the thyroid or the reproductive organs which is larger than the equivalent of a 5 mm diameter circle must not be used
describe stepwedge
- as it sounds
- When an image of the stepwedge is viewed, a full range of intensities should be seen, from a light grey at one end to almost black at the other
the image of the middle step (assuming a classic eleven step device) should have an optical density of 1.2 or so. If it didn’t, the exposure factors would need to be tweaked.
describe image lag test for fluoro
- view image of rotating test tool
- radioscopic system should be able to visualize a wire of diameter 0.013 inch or smaller
dose limts for technologists in training and students
as per the public (1 mSv /year)
how to best measure dose to fetus?
-TLD on abdomen
P value (max permissible weekly exposure) in R/week for diagnostics (is NCRP 49)
P=0.04 R/week for controlled
P= 0.002 R/week for uncontrolled
2 source rule for diagnostics
same as for linacs
max allowed leakage from diagnostic tube housing (equivalent to 0.1% from linac head)
0.115 mR/h at 1 m or 1 mGy/h
x-ray warning symbol for DI equipment
CAUTION: X-RAYS–ATTENTION : RAYONS X
-either have picture of xray tube in upside down triangle OR radiation trefoil symbol
maximum permissible size for fluoro minimum aperture
5cm X 5 cm
max radiation resulting from the transmission of the X-ray beam through, or scattered from, the entrance window of the radioscopic imaging assembly
2 mGy/h for entrance air kerma of 1 Gy/min
Gy to R conversion
1 Gy = 115 R
1 R = 8.73 mGy
