ch 8 mammography 2015 - ucsd radiology...

MammographyT.R. Nelson, Ph.D.

[email protected]

Radiology Physics Lectures: Mammography - 2015

• 2005 (in US) Women Men

• Invasive Breast Cancer Diagnosed 211,240 1,690• Noninvasive Breast Cancer Diagnosed 58,940 • Deaths from Breast Cancer 40,410 460

Radiology Physics Lectures: Mammography

Background and Perspective

• Breast Cancer is the most common form of cancer among women other than skin cancer

• Breast Cancer is the second leading cause of cancer death in women after lung cancer

• A woman's chance of developing breast cancer increases significantly with age.

• A woman's chance of developing breast cancer sometime in her lifetime is approximately 1 in 7

• The chance that breast cancer will be responsible for a woman's death is about 1 in 33

• If detected in the earliest stages, the five-year survival rate for breast cancer is 98%.


Background and Perspective


Mammography Evolution• Introduced in the early 1950’s– little medical benefit – poor image quality• Xerography introduced in 70’s and 80’s– high dose– good resolution and edge enhancement– poor contrast sensitivity• ACR mammography accreditation program– started mid 80’s– improved quality control– improved dosimetry• Mammography Quality Standards Act (MQSA)– passed in 1992


Mammography Evolution

• Ultrasound• Cyst / solid differentiation• Biopsy guidance• Operator dependent

• MRI• High contrast sensitivity• Visualize silicone implants• Breast cancer staging• Generally requires contrast

• Thermography• Infrared imaging


Complementary Imaging Technology


State-of-the-Art - Full Field Digital Mammography• X-ray mammography is current “gold

standard”

• Cancer identification– High contrast between normal and cancer

tissues– Detects calcifications



Soft Tissue Contrast - Breast

Contrast =(Gland -Cancer)

Glandx100


Mammography Equipment


Review Question


Review Question

ABDC


Mammography Equipment - X-ray Tube Design• Anode

– Molybdenum– Rhodium– Tungsten

• Characteristic radiation– Molybdenum - 17.5, 19.6 keV– Rhodium - 20.2, 22.7 keV

• Anode– Angle determines field-of-view– Cathode over chest wall– Anode over nipple– Grounded to reduce space charge


Review Question


Review Question


Mammography Equipment - X-ray Tube Design


Mammography Equipment - Anode - Cathode Axis


Mammography Equipment - Focal Spots

• Small focal spots– Reduce blurring– High magnification

• Size depends on use– 0.3 - 0.4 mm for contact imaging– 0.1 - 0.15 mm for magnification imaging

• Size depends on SID– 0.4 mm for SID > 66 cm– 0.3 mm for SID < 65 cm

• Size varies with position in field


Mammography Equipment - Focal Spot Size Variation


Mammography Equipment - Focal Spot Size Variation

Focal spot size estimated with slit camera or pinhole camera.Effective resolution measured with bar pattern (up to 20 lp/mm).

Measurement incorporates contribution of all components (i.e. image receptor, focal spot, tube motion, etc.)


Review Question


Review Question


Mammography Equipment - Beam Quality


Review Question


Review Question


Mammography Equipment - Filtration

X-ray Beam Filtration:Inherent: ~1 mm Be

Added: Mo, Rh eliminates low (and high) energy x-rays








Tungsten (W) characteristic x-rays from L shell





Review Question


Review Question


Mammography Equipment - HVL

• Half-value Layer (HVL)– Reflects beam “hardness”– How much soft radiation is present in beam• Small HVL - too much soft radiation

– Dose without information• Large HVL - more penetrating beam

– Aged or pitted anode– Too much filtration

– Depends on• Inherent filtration• Added filtration• Compression paddle composition






Review Question


Review Question


Mammography Equipment - Tube Output

Must have at least 7.0 mGy/sec at 28 kVp in Mo/Mo mode

to meet MQSA


Mammography Equipment - Collimation

Light - x-ray field congruence to <1% for any edge and <

2% overall

Must extend to chest wall


Mammography Equipment - Collimation


Mammography Equipment - Exposure Control

• Automatic Exposure Control– Uses sensor to monitor exposure– Shuts off at pre-determined amount of radiation– Compensates for breast thickness and density• May use short (< 100 ms) pre-exposure to set technique

– Designed to produce optimum and consistent density

– Adjustments to increase/decrease density– Includes a backup timer


Mammography Equipment - Exposure Control


Mammography Equipment - Technique Chart


Mammography Equipment - Compression

Improves image quality, reduces motion, decreases thickness, decreases blurring, lowers radiation dose





Spreads tissue over localized area


Review Question


Review Question


Mammography Equipment - Scatter - Primary Ratio


Review Question


Review Question


Mammography Equipment - Anti-scatter Grids


Review Question


Review Question

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Radiology Physics Lectures: Mammography - Magnification

• MTF of the focal spot decreases with increasing magnification• MTF of the detector increases with magnification• Optimum magnification depends on both focal spot MTF and

detector MTF• Geometric magnification derives no resolution improvement

from large focal spot - focal spot blur dominates• Geometric magnification shows resolution improvement when

detector has large detector pixels sizes - smaller effective pixel size

The focal spot MTF degraded with magnification while the detector MTF improved with magnification. Representa- tive results shown in Fig. 1 demonstrate that the improvement of the

MTF depended on the tradeoff between focal spot size and pixel size. A large focal spot (0.6 mm) resulted in little or no resolution improvement with the use of geometric magnification. Since the

focal spot blur dominated the system sharpness, reducing the effective pixel size did not compensate for the loss of resolution. A focal spot of 0.3 mm and pixel sizes of 50, 100, and 150

um showed an improvement in resolution for lower frequencies but not for higher frequencies suggesting a task dependent tradeoff for this combination (i.e., depending on the characteristics of the features that need to be imaged, different parameters may be optimal). A 0.3 mm focal

spot with a 200 um pixel size showed an improved MTF for all magnification values although there was an optimum magnification. Magnification with a 0.1 mm focal spot resulted in improved MTF out to very high frequencies regardless of pixel size; specifically for large pixel sizes as the resolution

of systems with large pixel sizes and small focal spots were dominated by the pixel size. Magnification in such systems resulted in a smaller effective pixel size thus increasing the overall

system resolution.

Geometric magnification increased the cut-off frequency of the system. The MTF was seen to improve with magnification for lower frequencies but a crossover point occurred for most

geometries, where the focal spot blurring became more dominant. The improvement in the MTF was particularly noteworthy for systems with larger pixel sizes and smaller focal spot widths since the effective pixel size in the object plane was reduced by magnification, thus reducing the overall

resolution of the system.

Boyce et.al. Imaging properties of digital magnification radiography, Medical Physics, 2006

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M = 1; 0.3 mm Focal Spot; 200 um Pixel SizeM = 2; 0.3 mm Focal Spot; 200 um Pixel SizeM = 3; 0.3 mm Focal Spot; 200 um Pixel Size

M = 1; 0.1 mm Focal Spot; 200 um Pixel SizeM = 2; 0.1 mm Focal Spot; 200 um Pixel SizeM = 3; 0.1 mm Focal Spot; 200 um Pixel Size

Object Plane Resolution

Source - Object

Distance

Object - Image

Detector Distance


Mammography Equipment - Screen-Film Systems





Limiting resolution approximately 20 lp/mm

Requires approximately 12-15 mR exposure for optimal ODRegular film requires approximately 2 mR




Review Question


Review Question



Processing quality control is essential to mammography success







Peak location shows where greatest contrast

occurs. Provides sensitive means to

monitor processor QC over time



Extended processing used to improve performance in standard film processors

• Optimal viewing requires:– High view box / monitor luminance (cd/m2)

• Mammography view box 3000 cd/m2

• Standard view box 1500 cd/m2

– Masking of non-image areas on view box– Low ambient light levels (< 50 lux or lumens/m2)

• Moon ~ 1 lux• Normal room lighting ~ 100 - 1000 lux

– Bright light should be available


Mammography Equipment - Viewing Conditions


Mammography Equipment - FFDMDigital Imaging Detector• Large dynamic range• Reasonable spatial resolution (300 µm)• Digital image -> input to CAD system• Expensive ~ $300k


Mammography Equipment - FFDM

Digital Detector Film-Screen


Mammography Equipment - Stereotatic Biopsy

Small field of view: 25 x 25 mm1k x 1k CCD detector - 25 µm






Mammography Equipment - Tomosynthesis

Tomosynthesis comparable dose to Projetion





Cranial-caudal conventional mammography view (A) of a middle-aged woman presenting with a palpable mass indicated by a metallic BB marker.

Tomosynthesis 1 mm thick image (B) depicts a circumscribed mass (arrow)Mark A. Helvie, , Digital Mammography Imaging: Breast Tomosynthesis and Advanced Applications, Radiol Clin North Am. Sep 2010; 48(5): 917–929



Vertical SectionProjection Tomo


Mammography Equipment - Dose

• Factors affecting dose– Speed (efficiency) of imaging system– Preferred image density– Breast thickness– Breast composition

• Fat less dense than gland– kVp selected

• High kVp better penetration• High kVp lower contrast• High kVp lower dose

• Filtration used• Mo or Rh

– Presence and type of grid• Typical Bucky factor ~2x






Glandular Dose (in mrad) for 1 Roentgen Entrance Exposure 4.2-cm Breast Thickness

Assumptions: 50% Adipose/50% Glandular Breast Tissue using a Mo/Rh Target-Filter

25 26 27 28 29 30 31 32 33 34 350.28 149 151 1540.29 154 156 158 1590.30 158 160 162 162 1630.31 163 164 166 166 167 1670.32 167 169 171 171 171 172 1720.33 171 173 175 176 176 176 176 1770.34 176 178 179 179 180 180 180 181 1810.35 180 181 183 183 184 185 185 186 1870.36 185 186 187 187 188 188 189 190 191 1910.37 189 190 191 191 192 193 193 194 195 1950.38 193 194 196 196 197 197 197 198 199 199 2000.40 202 203 204 204 205 205 206 207 208 208 2080.41 206 207 208 208 209 209 210 211 212 212 2120.42 211 211 212 212 213 213 214 215 216 216 2170.43 215 216 217 217 218 218 219 219 220 220 2210.44 220 220 221 221 222 222 223 223 224 224 2250.45 224 224 225 225 226 226 227 227 228 228 2290.46 228 229 229 230 231 231 232 233 233 2340.47 233 233 234 235 235 236 237 237 2380.48 238 238 239 240 240 241 241 242 2420.49 242 243 243 244 244 245 245 2460.50 247 247 248 248 249 250 2510.51 251 252 253 254 254 2550.52 257 257 258 258 2590.53 261 261 262 263 2640.54 265 266 267 2680.55 269 270 271 2720.56 275 276 2760.57 279 280 2810.58 284 2850.59 288 2890.60 293

kVp

HVL

Glandular Dose (in mrad) for 1 Roentgen Entrance Exposure 4.2-cm Breast Thickness

Assumptions: 50% Adipose/50% Glandular Breast Tissue using a Mo/Mo Target-Filter

22 23 24 25 26 27 28 29 30 31 32 330.23 119 1160.24 124 121 1240.25 128 126 129 1310.26 133 130 133 135 1380.27 138 135 138 140 142 1430.28 142 140 142 144 146 147 1490.29 147 144 146 148 150 151 153 1540.30 152 149 151 153 155 156 157 158 1590.31 156 154 156 157 159 160 161 162 163 1640.32 161 158 160 162 163 164 166 167 168 168 170 1710.33 166 163 165 166 168 169 170 171 173 173 174 1750.34 168 170 171 172 173 174 175 176 177 178 1790.35 174 175 176 177 178 179 180 181 182 183

HVL 0.36 179 181 182 183 184 185 185 186 1870.37 185 186 187 188 189 190 191 1910.38 190 191 192 193 194 195 1950.39 196 197 198 198 199 2000.40 201 202 203 204 2040.41 206 207 208 2080.42 211 212 2120.43 215 2160.44 2200.45

kVp

7.64 7.28

1.34 1.27

0.953

4.73 4.70

1.07 1.06

0.992

Entrance Dose (mGy - Console)Entrance Dose (mGy - Measured)Glandular Dose (mGy - Console)

Glandular Dose (mGy)mGy (meter/ESE)



Review Question


Review Question


Mammography Equipment - MQSA QA

• Mammography facilities must be:• Accredited by ACR (or agreement states)

– Meet standards• Initial qualifications of team

– Physicians, physicists, technologists• Continuing education of team• Continuing experience of team• Equipment• Quality control program• Image quality

• Certified by FDA– Granted when facility is accredited







ACR Phantom ACR insert(no scatter)

MammographyT.R. Nelson, Ph.D.

[email protected]


ch 8 mammography 2015 - ucsd radiology...

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