Density/Image Receptor Exposure in Radiography
Density/Image Receptor Exposure
INTRODUCTION
-Radiographic images require sufficient density/IR exposure (and contrast) to permit visibility of structural details
-Proper densities should be visualized throughout the anatomical area of interest
-The amount of black metallic silver remaining on a film after processing
-Digital images allow for post-processing; adjusting window level, will change monitor brightness
-Photographic property of density is termed density/IR exposure
ASSESSING DENSITY/IR EXPOSURE
Effects on image appearance
-The effects of technical factors and other influencing factors on density/IR exposure is not an exact science due to the multitude of variables in imaging systems
- Consider film/screen technology compared to digital and their respective response curves
-Challenge is to determine how to change technical factors to produce a visible change in density/IR exposure that still falls within acceptable limits
Factors affecting density/IR exposure
Milliampere-Seconds as the Controlling Factor
-There is a direct relationship between mAs and IR exposure
*As mAs increases; x-ray exposure (intensity) increases and image density increases
– Recall the D log E curve of film; film density is the log10 of opacity and opacity is the relationship of incident light over transmitted light
*Along the straight-line portion, density is ~ proportional to log relative exposure; therefore a doubling of exposure will result in a doubling of ____________.
An increase in mAs does not mean an increase in penetration
An increase in mAs = increase in exposure = increase in film density; a linear relationship
A minimum 25 – 35% change in mAs is necessary to cause a noticeable change in film density however…
Generally mAs is changed (re-exposing the patient) by either halving or doubling the original value
-Direct square law (density maintenance formula)
*As distance increases, intensity decreases resulting in a decrease in density
Direct square law →
Factors affecting density/IR exposure
Kilovoltage as an Influencing Factor
-An increase in kV = an increase in beam intensity and an increase in beam quality
-An increase in kV = increase in film density (not a linear relationship)
*4-5% change in kVp in 30 – 50 kV range
*8-9% change in kVp in 50 – 90 kV range
*10-12% change in kVp in 90 – 130 kV range
-Also, an increase in kV = increase scatter production which increases image density caused by fog
-The 15% rule is a rough guide to adjust and compensate for density/IR exposure changes
-“The 15% rule is somewhat accurate within the range of 60 to 100 kVp.”
*A 15% increase in kV causes a doubling of exposure to the IR therefore an increase in OD
*A 15% decrease in kV causes a halving of exposure to the IR therefore a decrease in OD
EXAMPLE of the 15% rule
A knee radiograph was obtained using 6 mAs and 75 kVp. What kVp is required to halve the exposure to the IR?
75 kVp x 15%
75 kVp x 0.15 = 11.25
75 – 11.25 = 63.75 → 64 kVp
-Will the contrast of the radiograph be affected? Explain.
FACTORS AFFECTING DENSITY/IR EXPOSURE
Other influencing factors
Focal spot size
-Focal spot blooming
*Focal spot size increases in direct proportion to the tube current
-Negligible when equipment is properly calibrated
Anode heel effect
-Alters the intensity of radiation between cathode and anode
*Thicker anatomy placed at cathode
Carlton P. 394 TABLE 26-2 Projections that may use the Anode Heel Effect to Advantage
Distance (SID and OID)
SID alters the intensity of the beam reaching the IR; Inverse Square Law (ISL)
→
mAs must be changed to compensate for a change in distance; Direct Square Law (DSL)
→
EXAMPLE of the DSL
A diagnostic image was produced using 4.5 mAs at 180 cm; what mAs will be required to maintain image quality at 100 cm?
mAs2 = à mAs2 = 1.4
Other influencing factors
Distance (SID and OID)
Variations in OID generally do not cause visible changes in density/IR exposure
Filtration
-Filtration and its ability to alter beam intensity affect density/IR exposure
-All types of beam filtration alter density/IR exposure; i.e. added filtration
-Density/IR exposure decreases when filtration is increased
Other influencing factors
Beam restriction
-Reducing the primary field size will reduce the total number of photons available
-The production of scattered radiation is reduced therefore the overall density/IR exposure is also reduced
-Generally, technical factors need to be altered, due to changes in density/IR exposure, under the following circumstances;
*Large anatomical part
*High kVp
*Low ratio grid
*Non-grid examinations
Other influencing factors
Anatomical part
-The patient is the primary beam attenuator and therefore has a great influence on density/IR exposure
-Amount of attenuation is dependent on; 1.Thickness of tissue
2.Tissue type: average atomic number and mass density
3.Presence of contrast media
4.Advanced pathology
*Depending on the type of contrast media (positive or negative) or the type of pathology (additive or destructive), an inverse or a direct relationship exists
5.Severe tube angles (> 15°)
*Special consideration when using severe tube angles, resulting in significant differences in tissue thickness across the beam
6.Cast material
*Adjustments for cast material should only be made if it increases the thickness of the body part when compared to the non-casted part
Other influencing factors
Grid construction
-The purpose of a grid is to absorb scatter; scatter radiation contributes to the density/IR exposure
-The following grid characteristics will reduce density/IR exposure;
*High ratio, low frequency, and dense interspace material
*Moving grids
*Improperly used grids
-When changing grid ratios, it is recommended to increase or decrease the mAs
-Note: Do not change the kVp because the benefit of the grid (improved image contrast) may be compromised
Grid conversion formula
GCF = Grid conversion factor
Example of grid conversion formula
A diagnostic abdomen radiograph was obtained using a 12:1 grid, 40 mAs, and 82 kVp. A second image is requisition using a 16:1 grid. What mAs is required to produce a satisfactory image?
mAs2 = à mAs2 = 49
Other influencing factors
Image Receptors
-Film/screen systems are classified according to speed known as Relative Speed (RS)
-As RS increases, the amount of exposure required to maintain the same density/IR exposure decreases
-Film processing
*Density will increase with;
1.Increase in developer temperature
2.Increase in developer processing time / immersion time
3.Increase in developer replenishment rates
September 19, 2017 at 10:19 am
Some tips i have observed in terms of laptop memory is there are specs such as SDRAM, DDR and the like, that must fit in with the requirements of the mother board. If the pc’s motherboard is fairly current while there are no main system issues, upgrading the storage space literally usually takes under an hour or so. It’s one of the easiest pc upgrade types of procedures one can visualize. Thanks for expressing your ideas.
August 14, 2014 at 8:30 am
Major thankies for the article.Really thank you! Will read on…
educational organization
August 8, 2014 at 7:15 am
Enjoyed every bit of your article post.Thanks Again. Awesome.
hearth products
August 7, 2014 at 8:08 am
Awesome article.Much thanks again. Cool.
electricien parisien
August 5, 2014 at 7:44 am
I loved your post.Really thank you! Great.
sex toys
August 4, 2014 at 4:23 am
Thanks so much for the blog post. Awesome.
legal steroids
August 1, 2014 at 12:47 pm
I value the post.Really thank you! Awesome.
Sydney Escorts
July 31, 2014 at 1:35 pm
I appreciate you sharing this article.Much thanks again.
Piyo
July 31, 2014 at 10:46 am
Great, thanks for sharing this blog post.Much thanks again. Awesome.
serrurier 77 seine-et-marne
July 31, 2014 at 8:16 am
A big thank you for your blog article. Will read on…
Funeral Plan Reviews
July 30, 2014 at 7:18 am
Im grateful for the article post. Really Cool.
uae dating
July 30, 2014 at 4:33 am
Appreciate you sharing, great post.Much thanks again.
best 7 inch tablet
July 29, 2014 at 7:01 am
I value the blog.Much thanks again. Fantastic.
shemorigirl
July 28, 2014 at 6:28 am
A round of applause for your article post. Much obliged.
counselling lincolnshire
July 26, 2014 at 4:03 am
Thanks again for the blog article. Awesome.
rhinoplasty surgeon Edmonton
July 25, 2014 at 4:16 am
Really informative blog article.Really thank you! Really Great.
Low cost mobile apps
July 24, 2014 at 4:10 am
Thank you for your article post. Awesome.
didsbury barbers
July 24, 2014 at 3:47 am
A big thank you for your blog. Fantastic.
surrealist art
July 23, 2014 at 9:51 pm
I’d personally really like to retire in San Raphael, France on the Mediterranean Sea. It is so lovely! I’d also function on learning French since incredibly few people there speak English.
July 23, 2014 at 7:28 am
Thanks-a-mundo for the blog.Much thanks again. Great.
Phoenix Plumber
July 23, 2014 at 3:13 am
Thanks again for the article.Really thank you! Really Great.
Glendale Painter
July 22, 2014 at 2:08 pm
Very neat blog.Thanks Again. Want more.
http://www.opiniepl.pl/wonga-opinie/
July 22, 2014 at 5:19 am
I am so grateful for your blog post.Really thank you! Want more.
Mathematics through Games
July 22, 2014 at 4:04 am
Thanks for sharing, this is a fantastic blog.Thanks Again. Cool.
shisha pen
July 21, 2014 at 12:16 pm
wow, awesome blog. Keep writing.
free online ecommerce store
July 21, 2014 at 6:17 am
Wow, great post.Really looking forward to read more. Much obliged.
giveawayoftheday
July 18, 2014 at 3:18 pm
Really appreciate you sharing this blog article.Really thank you! Much obliged.
web design
July 18, 2014 at 10:42 am
Really informative blog.Really thank you! Awesome.
security solutions
July 18, 2014 at 3:31 am
Thank you for your blog article.Much thanks again. Cool.
Real estate in Alanya
July 17, 2014 at 4:06 am
I value the article. Really Great.
ip address database
July 16, 2014 at 4:28 am
Great blog.Really looking forward to read more. Great.
garcinia cambogia
July 15, 2014 at 4:37 am
Really enjoyed this post.Thanks Again. Much obliged.
CDL Bus Driver jobs
July 14, 2014 at 1:34 pm
Im thankful for the post.Thanks Again. Awesome.
Dogecoin
July 14, 2014 at 1:25 pm
Thanks-a-mundo for the article.Much thanks again. Much obliged.
create a social network
July 14, 2014 at 10:41 am
This is one awesome post.Really thank you! Much obliged.
Colon Cancer Symptoms
July 12, 2014 at 3:01 pm
I am so grateful for your blog post.Really looking forward to read more.
baton rouge female gyms
July 12, 2014 at 10:43 am
Major thankies for the blog post.Much thanks again. Awesome.
shreveport knobs & pulls
July 12, 2014 at 5:37 am
Wow, great post.Thanks Again. Much obliged.
Ч‘Ч™ЧЄ Ч”Ч§Ч¤Ч” Ч‘Ч™ЧЁЧ•Ч©ЧњЧ™Чќ
July 10, 2014 at 12:26 pm
Great blog.Thanks Again. Really Great.
huile essentielle
July 10, 2014 at 4:37 am
Appreciate you sharing, great article post. Really Great.
hawkesbury tow trucks
July 8, 2014 at 9:08 am
A big thank you for your article post.
pakistani online tv channels
July 6, 2014 at 4:16 pm
Major thankies for the blog article.Thanks Again. Will read on…
Financial Assistance for Gastric Bypass
May 11, 2014 at 6:26 pm
Fantastic blog article. Great.