Mammography. Background and Perspective. Mammography Evolution. Background and Perspective. T.R. Nelson, Ph.D. x41433

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1 Background and Perspective 2005 (in US) Women Men Mammography Invasive Breast Cancer Diagnosed 211,240 1,690 Noninvasive Breast Cancer Diagnosed 58,940 Deaths from Breast Cancer 40, T.R. Nelson, Ph.D. x41433 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%. 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

2 Mammography Evolution Complementary Imaging Technology Ultrasound Cyst / solid differentiation Biopsy guidance Operator dependent MRI High contrast sensitivity Visualize silicone implants Breast cancer staging Generally requires contrast Thermography Infrared imaging 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

3 Soft Tissue Contrast - Breast Mammography Equipment Contrast = (Gland - Cancer) x100 Gland C D B A

4 Mammography Equipment - X-ray Tube Design Anode Molybdenum Rhodium Tungsten Characteristic radiation Molybdenum , 19.6 kev Rhodium , 22.7 kev Anode Angle determines field-of-view Cathode over chest wall Anode over nipple Grounded to reduce space charge Mammography Equipment - X-ray Tube Design

5 Mammography Equipment - Anode - Cathode Axis Mammography Equipment - Focal Spots Small focal spots Reduce blurring High magnification Size depends on use mm for contact imaging 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.)

6 Mammography Equipment - Beam Quality

7 Mammography Equipment - Filtration X-ray Beam Filtration: Inherent: ~1 mm Be Added: Mo, Rh eliminates low (and high) energy x-rays Mammography Equipment - Filtration Mammography Equipment - Filtration

8 Mammography Equipment - Filtration Mammography Equipment - Filtration Tungsten (W) characteristic x-rays from L shell Mammography Equipment - Filtration

9 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 Mammography Equipment - HVL Mammography Equipment - HVL

10 Mammography Equipment - Tube Output Mammography Equipment - Collimation Must have at least 7.0 mgy/sec at 28 kvp in Mo/Mo mode to meet MQSA Light - x-ray field congruence to <1% for any edge and < 2% overall Must extend to chest wall

11 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

12 Mammography Equipment - Compression Mammography Equipment - Compression Improves image quality, reduces motion, decreases thickness, decreases blurring, lowers radiation dose Mammography Equipment - Compression Spreads tissue over localized area

13 Mammography Equipment - Scatter - Primary Ratio

14 Mammography Equipment - Anti-scatter Grids - Magnification Source - Object Distance $"!#,"!#+" M = 1; 0.3 mm Focal Spot; 200 um Pixel Size M = 2; 0.3 mm Focal Spot; 200 um Pixel Size M = 3; 0.3 mm Focal Spot; 200 um Pixel Size M = 1; 0.1 mm Focal Spot; 200 um Pixel Size M = 2; 0.1 mm Focal Spot; 200 um Pixel Size M = 3; 0.1 mm Focal Spot; 200 um Pixel Size!#*" Object - Image Detector Distance MTF of the focal spot decreases with increasing magnification MTF of the detector increases with magnification Optimum magnification depends on both focal spot MTF and detector MTF Geometric magnification derives no resolution improvement from large focal spot - focal spot blur dominates Geometric magnification shows resolution improvement when detector has large detector pixels sizes - smaller effective pixel size!"#$!#)"!#("!#'"!#&"!#%"!#$" 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, Object where the Plane focal spot blurring Resolution became more dominant. The improvement in the MTF!"!" (" $" $!" %" resolution of $(" the &" system. %!" '" %(" &!" )" %&'(')$#*+,-+./0$1)&2334$ 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 Boyce et.al. Imaging properties of digital magnification radiography, Medical Physics, 2006

15 Mammography Equipment - Screen-Film Systems Mammography Equipment - Screen-Film Systems Mammography Equipment - Screen-Film Systems Mammography Equipment - Screen-Film Systems Limiting resolution approximately 20 lp/mm Requires approximately mr exposure for optimal OD Regular film requires approximately 2 mr

16 Mammography Equipment - Screen-Film Systems Mammography Equipment - Screen-Film Systems Processing quality control is essential to mammography success

17 Mammography Equipment - Screen-Film Systems Mammography Equipment - Screen-Film Systems Peak location shows where greatest contrast occurs. Provides sensitive means to monitor processor QC over time Mammography Equipment - Screen-Film Systems Extended processing used to improve performance in standard film processors Mammography Equipment - Viewing Conditions Optimal viewing requires: High view box / monitor luminance (cd/m 2 ) Mammography view box 3000 cd/m 2 Standard view box 1500 cd/m 2 Masking of non-image areas on view box Low ambient light levels (< 50 lux or lumens/m 2 ) Moon ~ 1 lux Normal room lighting ~ lux Bright light should be available

18 Mammography Equipment - FFDM Mammography Equipment - FFDM Digital Imaging Detector Large dynamic range Reasonable spatial resolution (300 µm) Digital image -> input to CAD system Expensive ~ $300k Digital Detector Film-Screen Mammography Equipment - Stereotatic Biopsy Mammography Equipment - Stereotatic Biopsy Small field of view: 25 x 25 mm 1k x 1k CCD detector - 25 µm

19 Mammography Equipment - Stereotatic Biopsy Mammography Equipment - Tomosynthesis Tomosynthesis comparable dose to Projetion Mammography Equipment - Tomosynthesis Mammography Equipment - Tomosynthesis 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):

20 Mammography Equipment - Tomosynthesis Vertical Section Projection 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 Mammography Equipment - Dose Mammography Equipment - Dose

21 Mammography Equipment - Dose Glandular Dose (in mrad) for 1 Roentgen Entrance Exposure 4.2-cm Breast Thickness 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 Assumptions: 50% Adipose/50% Glandular Breast Tissue using a Mo/Rh Target-Filter kvp HVL Entrance Dose (mgy - Console) Entrance Dose (mgy - Measured) Glandular Dose (mgy - Console) Glandular Dose (mgy) mgy (meter/ese) HVL kvp 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

22 Mammography Equipment - MQSA QA Mammography Equipment - MQSA QA Mammography Equipment - MQSA QA Mammography Equipment - MQSA QA

23 Mammography Equipment - MQSA QA Mammography Equipment - MQSA QA Mammography Equipment - MQSA QA Mammography T.R. Nelson, Ph.D. x41433 tnelson@ucsd.edu ACR Phantom ACR insert (no scatter)