Physical & Technical Aspect of Mammography

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PHYSICAL & TECHNICAL ASPECT OF

MAMMOGRAPHY

ByDr. A. O Adeyinka

Presented at the Physics Update Course atLUTH

February 14th – 18th 2005



OBJECTIVES OF MAMMOGRAPHY

• Obtain Information about differences in Type &Structure of Tissues of the Breast

• Optimize Information Content of Mammography

• Describe how this Image is Generated within the

framework of Physical, Technical & RadiationProtection criteria, Inorder to render Diagnostic

opinion



MAMMOGRAPHY IMAGING CHAIN

Pathway of X-Rays in Tube to Interpretation

X-RAY TUBE ASSEMBLY

•Anode Material

•Filter

•Tube Voltage

IMAGE RECEPTOR

•Sensitivity

•Contrast

•Resolution

•Noise

RADIOGRAPHIC DEVICE

•Focal Spot

•Geometrical Configuration

•Scattered Radiation

BREAST

•Thickness

•Tissue Composition

IMAGE QUALITY

•Radiation Exposure



DEDICATED MAMMO - EQIUPMENT

Composition (Film-Screen Mammo)• Special Focal Spot

• Target & Filter Materials

• Low Kilovoltage

• Compression Device designed to optinize the

Mammographic Image at Low Radiation Dose



STEP 1- GENERATION OF THE X-RAYS

Factors that Determine Transparency of BreastTisue in Displayed Image

•Tube Voltage

•Anode Materials

•Type & Thickness of Added Filter



TUBE MATERIALS

(MOLYBDENUM & TUNGSTEN)

Molybdenum:

•Uses 0.03mm Molybdenum Filteration

•Produces Low Kilo-electron Volt X-Rays

•Xteristic Peak Volt 17.9 & 19.5 Kev which

provides high Contrast Breast Image of average

thickness

•>20Kev Photons are suppressed by Filters

•Kvp settings = 25-28Kvp



TUNGSTEN TARGET:

•

Uses a Beryllium Window and Aluminum Filter •At Low Kvp, Tungsten produces High Energy

Photons with Low Subject Contrast

•Kvp settings = 22-26Kvp

New Mammo-Equip

•Uses Tungsten Target + Berylium Window plus aMolybdenum or Rhodium K-edge Filter to produce

High Contrast Images

•Thick/Dense Breast – 0.05 Rhodium Filter at high Kv



Factors that Determine the Maximum

Attainable Resolution of Imaging System

1. Focal Spot Shape & Size• Helps to produce high Resolution

• Helps to Reduce Geometrical Blurr

• Size should be kept Small• Dist b/w Breast & Image receptor should be

Smaller

•Maximize Object to Focal Spot Distance

• In Magnification Work – FS size should not begreater than 0.3mm ( Range 0.1-0.2mm)



2. Geometrical Configuration of Radiographic Device

• Image Display achieved by Relative Absorption of

X-Rays in Tissue

• Pathway: X-RaysBreastModulated by

Absorption & ScatteringImage Receptor

• Radiation Image=Distribution of X-Ray Intensity atPlane of Image Receptor

• Radiation Image carries Information extracted from

the tissue as the Distrbution of Intensity & directionof the X-Rays

• The Information can only be Selectively

Emphasized or suppressed or Eliminated



Step 3- Image Improvement

Anti-Scatter Grid

•Radiation Image consist of PRIMARY (contains the

entire Image Information) & SCATTERED Radiation

•Primary Radiation (Primary Contrast) is caused byAttenuation (Absorption & Scattering)

•Scattering diminishes the Intensity Differences in

Primary Radiation

•Grid Modifies the Radiation Beam b/4 reaching

Image Receptor, by absorbing the Scattered radiation

to a greater degree than Primary radiation



•Grid Improves Image Contrast by reducing Scatter

•

There is Concomitant increase in Patient Dose•The Increase in Radiation Dose with Grid is about

2Times that of Non-Grid, but thjis may be

Compensated by a Faster Screen-Film combination

•More Useful in Thick Dense Breast

•Typical Reciprocating Grid = 16micro.m lead strips

separated by 300micro.m Carbon Filter Resin

Interspace

•

Dedicated Machines-Grid Ratio of 5:1

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Physical & Technical Aspect of Mammography