Philips Microdose Mammography -the Technology

AAPM 54th Annual Meeting
Charlotte, North Carolina
August 2, 2012
Philips Microdose Mammography
-the Technology and Physics Behind
the First FDA Approved Photon
Counting X-ray Imaging System
Mats Danielsson
Royal Institute of Technology (KTH)
Stockholm,Sweden
[email protected]
Physics of Medical Imaging at the Royal
Institute of Technology in Stockholm
Disclosure Statement
Founder of Sectra Mamea AB which was
acquired by Philips.
1
Challenges in Mammography Today
•10-40% of cancers missed
•Recall rate 1%-20%
•Cost
•Radiation Dose
•Dense breasts !
What may help us?
-Get rid of superimposed tissue
-Visualize blood vessels associated to
the cancer with contrast agent
-Visualize the cancer with dual energy
(spectral imaging)
-More efficient sensors
Fundamental Problem:
Fundamental problem:
”Convert an x-ray photon into electric
charge which you measure”
2
Who counted photons first?
What was that?
Maybe a photon
To Count Photons – No Electronic Noise
Energy
X-ray photon
Threshold 1
Threshold 2
Threshold 3
Noise
1
2 3
Time
Integrating Current:
Today’s praxis in X-ray Imaging
Energy
X-ray photons
1
Time
3
• Comparison of FFDM Technologies
aSi flat panel
aSe flat panel
Photon Counting
X-ray Photon
X-ray Photon
X-ray Photon
Scintillator
amplification
Light
Analog
Capacitor charge
storage
Analog signal
A/D - Converter
Digital signal
aSe
X-ray into electrons
MicroDose
Detector
Electrons
Analog
Capacitor charge
storage
Analog signal
A/D - Converter
Digital signal
5 (00000000000101)
Digital signal
1
What is difficult with photon
counting?
Measured Effect of Dead Time
R.L. Lucke Rev. Sci. Instrum. 47 (6):766 (1976)
E. Fredenberg et al. SPIE 7258 (2009)
4
Measured Effect of Dead Time
Deadtime per event
189 ns
Deadtime at 20 kHz
0.4%
Deadtime at 200 kHz
3.7%
E. Fredenberg et al. SPIE Physics of Medical Imaging 2009
Philips – Photon Counting
Mammography Today
Crystalline Silicon Detector
5
Crystalline Silicon for Photon Counting
Spatial resolution
Spatial Resolution in Mammography
50 µm MicroDose Image
100 µm Image
1
Calcifications Case
CC Close ups (from study by Cole et al.)
FFDM
Microdose
6
“Diagnostic Scan” is Microdose
alternative to Geometric Magnification
Use high DQE and deploy higher dose on the
spot compression area. No magnification table.
•
Phantom evaluation shows Diagnostic Scan
achieves better image results at a lower dose
compared to Geometric Magnification.
•
“Performs comparably or better than
conventional geometric magnification for the
detection of masses and micro-calcifications,
with the exception of mass lesions in larger
breast, where GE conventional geometric
magnification yields superior results” according
to Egan et al, IWDM Philadelphia, PA (2012)
Photon Counting
CONFIDENTIAL
Virtually Eliminates all Scatter Radiation
Conventional
Scatter
Photon Counting
No Scatter
7
Scattered radiation
DQE at Zero Spatial Frequency
DQE(0)
PHILIPS MicroDose
Photon Counting
Monnin et al. Med. Phys., vol. 34 (3), pp. 906-914, 2007
System DQE
Åslund, M. et al., 2010. Detectors for the future of x-ray imaging. Radiation
Protection Dosimetry, 139(1-3), pp. 327-333
8
Does the clinical performance
match the physics?
Example 1:
Experience from BreastCheck, The Irish
Breast Screening Program
• 4 static & 16 mobile
screening units
• Equipment:
– 11 CsI scintillator
– 10 a-Se
– 7 Photon counting
Ireland Breast Screening Program
Cancer Detection Rates
Mccullagh et al. The British Institute of Radiology
(2011),
The British Institute of Radiology, doi: 10.1259/bjr/29747759
doi: 10.1259/bjr/29747759
9
Ireland Breast Screening Program
Cancer Detection Rates
Mccullagh et al. The British Institute
of Radiology (2011),
The British Institute of Radiology, doi: 10.1259/bjr/29747759
doi: 10.1259/bjr/29747759
Ireland Breast Screening Program
Radiation Dose
Average Mean Glandular Dose
1.6
1.4
1.2
Philips MicroDose*
mGy
1
GE Essential
0.8
0.6
Hologic Selenia
0.4
0.2
0
P Baldelli et. al., “Comprehensive Dose Survey Of Breast Screening In
Ireland”, Radiation Protection Dosimetry , Vol. 145, No. 1, pp. 52–60, 2010
Example 2:
E Cole, A Toledano, M Lundqvist, E Pisano
"Comparison of Radiologist Performance with
Photon-Counting Full-Field Digital Mammography to
Conventional Full-Field Digital Mammography”
Academic Radiology, Vol 19,(8) p 916-922, August
2012
10
Microdose versus standard FFDM
•
•
Multi-slit Scanning Full-Field Digital Mammography System with
Photon Counting Detector (Philips Mammography L30)
Comparison Study between Philips L30 and GE FFDM conducted in
2010
– Multi-Case, Multi-Reader Study
– Feature Analysis Study
– Assessment of Dose Differences based on Breast Density, Breast
Thickness
Microdose versus standard FFDM
•
•
16 MQSA qualified Radiologist Readers
133 women (≥ age 40) from two European Sites: one in United
Kingdom and one in Switzerland
– 67 women were in the Normal Cohort (underwent Philips Microdose
Mammography as part of their routine screening exam after having had a
GE FFDM screening mammogram 10-30 months prior) [67 normal].
– 66 women were in the Diagnostic Cohort (had a screening Philips MDM
mammogram and underwent diagnostic imaging with GE FFDM) [17
biopsy benign, 49 cancer]
•
Review Workstations at ACR Image Metrix Facility in Philadelphia, PA
Microdose versus standard FFDM
•
•
Each reader reviewed all 133 cases at two separate visits at
least one month apart. Modalities were counterbalanced.
Readers evaluated the images for presence of suspicious
findings providing a BIRADS score(1-5) and a Probability of
Malignancy score 0-100
11
Microdose versus Standard FFDM
Philips L30
GE FFDM
Difference
pvalue
AUC
0.947 (0.920,
0.974)
0.931 (0.898,
0.964)
0.016 (-0.001,
0.034)
<0.001
Sensitivity
0.936 (0.897,
0.976)
0.908 (0.856,
0.960)
0.028 (-0.003,
0.059)
<0.001
Specificity
0.764 (0.688,
0.841)
0.749 (0.668,
0.830)
0.015 (-0.022,
0.052)
<0.001
Feature analysis resulted in Microdose being preferred
to standard FFDM by the readers for >70% of the cases
The average mean glandular dose for Microdose was
0.74 mGy
FFDM average mean glandular dose was 1.23 mGy
Further clinical trials
Evidence from clinical trials:
B. Hedson et al, "Digital vs. Screen-Film
Mammography: A retrospective Comparison in a
Population-Based ScreeningProgram”, European
Journal of Radiology, Volume 64, Issue 3, p 419-425
S Weigel , R Girnus , J Czwoydzinski , T Decker , S
Spital , W Heindel “Digital mammography screening:
average glandular dose and first performance
parameters.Rofo. 2007 Sep ;179 (9): p 892-895
M.G. Wallis, “Evaluation and Clinical assessment of
Digital Mammography Screening using a Sectra
Microdose full field Digital X-ray unit”, NHSBSP
Equipment Report 0601, NHS Cancer Screening
Programmes 2006
E
Silicon is Proven Material
Transport & storage not a problem
temperatures from -10 C to 50 C
3
12
Also…
-You need to be ready for the next
photon, no “recovery time” for detector
between exposure.
-Curved surface and warm patient
support = patient comfort
3
Philips MicroDose status summary
-Low dose and high image quality
3
But what will happen in the future?
3
13
Challenges in Mammography Today
•10-40% of cancers missed
•Recall rate 1%-20%
•Cost
•Radiation Dose
•Dense breasts !
What may help us?
-Get rid of superimposed tissue
-Visualize blood vessels associated
to the cancer with contrast agent
-Visualize the cancer with dual
energy (spectral imaging)
-More efficient sensors
HighReX - a European Union Project
42
14
HighReX
Objectives
•Develop novel imaging methods using
– 3D
– dual energy
– contrast mammography
•with improved detection and diagnosis of breast cancer compared
to current technology
Multi-center clinical trial
Finalized 2010
Duration: 3.5 years
HighReX project
Coordinator, (M. Danielsson)
system supplier
• Sectra Mamea AB, Sweden (aquired by Philips Sep. 2011)
Clinical Partners
• Addenbrooke’s Hospital, Cambridge, UK (M. G. Wallis)
• S:t Göran’s Hospital, Stockholm, Sweden (K. Leifland)
• Charité Hospital, Berlin, Germany (F. Diekmann)
• Münster University Hospital, Munster, Germany (W. Heindel)
• Health Unit of Pistoia, Florence, Italy (M. Rosselli del Turco)
• Arcades, Marseille, France (B. Seradour)
Other partners
• Royal Surrey County Hospital NHS Trust
• Stichting Landelijk Referentie Centrum voor Bevolkingsonderzoek
• Radboud University Nijmegen Medical Centre
Photon Counting
Tomosynthesis
4
15
Geometry
Geometry
Projections
Reconstructed volume
Photon Counting Tomosynthesis
•
Scanning multi-slit system
– Virtually no scatter radiation
– Short exposure time (~1 s)
•
Photon counting detector
–
–
–
–
Intrinsically fast image read-out
Lower x-ray dose without compromising image quality
No electronic noise (especially important in tomo)
High resolution 50 micron pixel
16
Technical Data
• X-ray tube and detector move in a synchronized
motion
• Tomosynthesis angle: 11 degrees
• Scan angle of x-ray tube: +/- 17 degrees
• Exposure time for a point << total scan time (~1
second exposure time)
• Projections: 21 – one per detector line
• Dose level from current clinical trial, prototype: 0.8
mGy for average breast,
HighReX Cases
2D
Tomo
17
Spiculated mass
2D
Tomo
Cyst
2D
Tomo
Spiculated mass
2D
Tomo
18
Tomosynthesis Clinical Results
•
•
•
•
•
Photon counting tomo vs FFDM
10+10 readers, 130 cases (40 cancers, 24 benign, 66 normals)
Results published in Radiology 2012 (1): Two-view
tomosynthesis outperforms FFDM for less experienced
radiologists (< 10 yrs) when measured as AUC scores for
diagnostic accuracy, and also when measured by lesion type for
masses and calcifications separately.
No significant differences for one-view tomosynthesis vs FFDM
Photon counting tomo dose was only 0.7-0.82 mGy
(1) Two-View and Single-View Tomosynthesis versus Full-Field Digital
Mammography: High-Resolution X-Ray Imaging Observer Study Radiology March
2012 262:3 788-796; Published online January 24, 2012,
doi:10.1148/radiol.11103514
From: Marian Strassner [mailto:[email protected]]
Sent: 17 May 2012 22:38
To: Wallis, Matthew
Subject: Your article in Top 10 Most Read Dear Dr Wallis, We are pleased to
inform you that your article Matthew G. Wallis, Elin Moa, Federica Zanca,
Karin Leifland, Mats Danielsson
Two-View and Single-View Tomosynthesis versus Full-Field Digital
Mammography: High-Resolution X-Ray Imaging Observer Study
Radiology Mar 01, 2012 262: 788-796. has been listed as one of the ‘Top 10
Most Read Recent Articles’ in Radiology for the last 3 months (FebruaryApril 2012).
Contrast Agent
5
19
HighReX
•
Clinical trials
o
2010
o
Charité University
Hospital Berlin
o
Dr. Felix Diekmann
o
Iodine Enhancement
•
35 mm invasive lobular
carcinoma
Difficult to detect in 2D
Difficult to detect in
tomosynthesis
Energy subtraction –
clear improvement in
this case
•
•
•
Courtesy Dr. Felix Diekmann
Spectral Imaging
5
Single-shot spectral mammography
Energy
Photons
Threshold 1
Noise
1
2 3
Time
60
20
Single-shot spectral mammography
Energy
Low-energy
Photon
High-energy
Photons
Threshold 2
Threshold 1
Noise
1
1 2
Time
61
6
On the photo you can tell what is what…
Acrylic
Acrylic
Aluminum
Aluminum
Acrylic
CONFIDENTIAL
6
But on the X-ray image, can you tell what
is what?
CONFIDENTIAL
6
21
On photon counting
spectral you can!
Spectral image of
Aluminium
All acrylic removed
Al Al
Spectral image of acrylic
Aluminum removed
Single-shot spectral imaging
Applications for single-shot spectral
mammography in screening
1) Breast density measurements *
Providing the radiologist with objective
data to assess individual risks
2) Lesion evaluation*
Information acquired with the
regular mammogram
- no extra views
- no extra acquisition time
- no extra radiation
- no contrast injection
Providing the radiologist with objective
data to help assess suspicious lesions
And much more to come…
66
6
22
Spectral imaging - breast density measurements
Why?
fatty
dense
Breast cancer risk
Mammography sensitivity
Spectral imaging - breast density
measurements
How does it work?
Glandularity: 16%
BIRADS code: 1
DICOM structured report
DICOM header data
68
Spectral imaging - breast density
measurements
What are the benefits?
•
•
Objective data to assess and
classify breast density
Enables personalized care
- Choice of modality
- Screening interval
- Reader focus and efforts
fatty
dense
23
Spectral imaging - lesion evaluation
Why?
•
Recalls for benign findings are
a major problem in screening
– Increased costs – The cost of
diagnostic workup and
assessment of a recall is
approximately eight times the cost
of the screening
– Unnecessary stress and exam for
women
•
Up to 20% of recalls are due to
circular lesions which are easy to
detect but difficult to characterize
70
Spectral imaging - lesion evaluation
How does it work?
Lesion content:
Lesion diameter:
Lesion thickness:
Breast thickness:
ROI glandularity:
Water
13 mm
6 mm
39 mm
28%
Spectral imaging - lesion evaluation
What are the benefits?
•
For the radiologists
– Objective data to evaluate lesions water content
– Reduced costs generated by unnecessary recalls
•
For the woman
-
Possibility to avoid uneccessary exams and stress
Low dose
24
Publications
•
SPIE 2009
– A photon-counting detector for dual-energy breast tomosynthesis, E. Fredenberg, M.
Lundqvist, M. Aslund, M. Hemmendorff, B. Cederstrom, M. Danielsson
The photon-counting detector enables dual-energy subtraction imaging with electronic spectrum
splitting. This improved the detectability of iodine in phantom measurements, and the detector
was found to be stable over typical clinical acquisition times.
•
SPIE 2010
– Observer model optimization of a spectral mammography system, E. Fredenberg, M.
Lundqvist, M. Aslund, B. Cederstrom, M. Danielsson
•
SPIE 2011
Evaluation of photon-counting spectral breast tomosynthesis, N. Dahlmana, E. Fredenberga,
M. Åslund, M. Lundqvist, F. Diekmann, M. Danielsson
It was shown experimentally that unenhanced spectral imaging may increase detectability of
tumors in the order of a factor two if anatomical noise dominates. The model comparison
revealed that contrast-enhanced spectral imaging and tomosynthesis can be combined to
improve tumor detectability.
– Optimization of mammography with respect to anatomical noise, E. Fredenberg, B. Svensson,
M. Danielsson, B. Lazzari, B. Cederstrom
Publications
•
•
SPIE 2012
– Lesion characterization using spectral mammography, E. Fredneberg PhD, K. Leifland MD, B.
Norell PhD, B. Cederström PhD, M. Lundqvist PhD
– Photon-Counting Spectral Phase-Contrast Mammography, E. Fredenberg, E. Roessl, T.
Koehler, U. van Stevendaal, I. Schulze-Wenck, N. Wieberneit, M. Stampanoni, Z. Wang, R. A.
Kubik-Huch, N. Hauser, M. Lundqvist, M. Danielsson, M. Åslund
– Prof. Dr. Walter Heindel, Referenzzentrum Mammographie, Am Universitätsklinikum Münster,
Münster, Germany
Other
– Contrast-enhanced spectral mammography with a photon-counting detector, E. Fredenberg,
M. Aslund, M. Hemmendorff, B. Cederstrom, M. Danielsson, Med. Phys. (2010) Vol. 37, No. 5,
May
– Energy resolution of a photon-counting silicon strip detector, E. Fredenberg, M. Aslund, M.
Lundqvist, B. Cederstrom, M. Danielsson, Nucl. Instr. and Meth. (2010) Vol. 613, No. 1, pp.
156-162
– Detectors for the future of X-ray imaging, E. Fredenberg, M. Aslund, M. Telman, M.
Danielsson, Radiation Protection Dosimetry (2010), Vol. 139, No. 1–3, pp. 327–333
Does it help?
• Contrast agent
-Yes (but not in screening)
• Spectral Imaging
-Maybe
• Tomosynthesis
-No
25
Quality Control and Physics
Measurements
Philips Micodose QC philosophy
• Based primarily on
– IEC standards (e.g. IEC 61223-2-10, IEC 61223-32)
– European guidelines for quality assurance in breast
cancer screening and diagnosis, 4th Ed. (European
Comission)
– MQSA
– Our own experience and knowledge about critical
system parameters
Overview of Some Medical
Physicist QC Tests
For detailed step-by-step procedures for all tests please see the
QC manual or contact David Nelson [email protected]
26
Structure of QC procedures
Frequency
Performed by
Daily
Weekly
Monthly
QC technologist
Quarterly
Annual
Medical physicist
Medical Physicist QC procedures –
Annual
Annual
1
X-ray tube output
2
Air kerma reproducibility
3
Half value layer (HVL)
4
AEC: Breast thickness tracking
5
AEC: Density compensation
6
Image quality evaluation
7
CNR reference level
8
Tube voltage
9
Image field and x-ray field agreement
10
Missed tissue at chest wall
11
Viewing conditions
12
Guidance system control
MicroDose Differences
-Good to know for the physicist
27
Spatial resolution?
Different blurring mechanisms in the two directions
Spatial resolution, cont.
•
Slit-direction:
– Similar to other systems:
resolution best on patient support in the MicroDose
•
Scan-direction:
– Opposite to other systems:
resolution best farthest up in the MicroDose
MTF at two heights
On breast support
5 cm above
MTF 6 cm from chest wall and on pat. supp.
1
Slit dir.
Scan dir.
Slit dir.
Scan dir.
0.9
0.8
0.8
0.7
0.7
0.6
0.6
MTF [r.u.]
MTF [r.u.]
0.9
0.5
0.5
0.4
0.4
0.3
0.3
0.2
0.2
0.1
0
MTF 6 cm from chest wall and 5 cm above pat. supp.
1
0.1
0
2
4
6
8
10
12
Spat. freq. [lp/mm]
14
16
18
20
0
0
2
4
6
8
10
12
Spat. freq. [lp/mm]
14
16
18
20
28
Spatial resolution, cont.
•
Slit-direction: MTF factors
– Focal spot length
– Pixel size
•
Scan-direction: MTF factors
– Focal spot width
– Collimator slit width
Recommended test
•
Monthly QC test using line pair phantom placed on top of BR12 or
acrylic plate (~45 mm)
Both parallel and perpendicular to scan direction
Only technologist needs to perform this test
Pass criteria is visibility >= 6 lp/mm
We would like the physicist to be aware of the test
•
•
•
•
MicroDose – mAs
By mAs we mean effective mAs
•
•
•
•
•
Conv. mAs = tube current × exposure
time
Eff. mAs = tube current ×
(eff. exposure time for one point in image)
Eff. mAs = conv. mAs ×
open width in collimator
/ total scan length
Eff. mAs ≈ conv. mAs × 1%
If not explicitly stated otherwise we
always mean eff. mAs
Multi-slit collimator
Scan
direction
Detector lines
29
MicroDose – mAs
By mAs we mean effective mAs
•
•
Conv. mAs = tube current × exp. time
Eff. mAs
= tube current ×(eff. exposure time for one point in image)
= conv. mAs × open width in collimator / total scan length
≈ conv. mAs × 1%
Pulse duration = 10- 50 msec
Pulse freq = 5-30 per sec
Required Tools for Medical
Phycisist QC
Medical Physicist Required Tools
30
Medical Physicist Required Tools (contd.)
Tube Output Measurements Considerations
• Radiation to detector is pulsed (ensure your dose meter can handle it)
• W/Al anode/filter combination (meter calibrated for e.g. Mo/Mo can
give very wrong results)
• Scale dose using inverse square law to 45 mm above patient
support. Source-to-patient support = 640 mm
• Measured values should be within
+/-20% of system calculated
• Air Kerma reproducability
Unfors jig for dose measurements
must be within 5% rel. stdev
HVL
•
•
•
•
•
Use ion chamber or other dose meter calibrated* for the radiation
quality of the MicroDose system (W anode and 0.5mm Al filtration).
Place compression paddle 9 cm above patient support to minimize
scatter effects.
Place a lead sheet with hole on paddle.
Verify collimator is lined up with dose
meter.
Place Al filters on lead sheet as required.
* Ion chambers work fine
Solid state detectors
- Unfors is calibrated
- In discussions with RadCal and Keithly
31
Exposure and CNR Test
•
•
•
•
•
•
•
•
•
•
Verifies AEC ensuring optimal exposure
Acrylic is not equivalent to breast tissue
Flat acrylic on curved surface introduces bias
System corrects for thickness measurement
Test uses acrylic plates 20-70 mm
and 0.1/0.2 mm Al filter
Use ROI tool to calculate CNR
Use HVL and air kerma to calculate AGD
- use breast thickness not acrylic thickness
AGD = ESAK x g x c x s (QC manual)
Measured AGD shall be within 15% of system value
CNR should exceed CNR threshold (QC manual)
±
~13 mm
gap
Phantom Image Quality
•
•
•
•
Acquire ACR phantom image (no disk)
Score the phantom on AWS or RWS
At least 4 fibers, 3 groups of micro-calcifications, and 3 masses
must be seen (total score must be at least 10)
Calculate dose and should not exceed 1 mGy
CNR Reference Level
•
•
•
•
•
Establish operating level of CNR
Phantom available from Philips
Use Daily Quality Control (DQC) tool
Measure CNR and establish reference value
QC Tech to ensure daily CNR is within +/-10% of reference
32
SNR Test
• To check if constant SNR is maintained regardless of breast transmission
• Acrylic slabs 30-50 mm in 5 mm steps
• Use ROI tool
• SNR calculated for each slab thickness
• Measured SNRs to be within +/- 15% of average SNR value
Summary
-Important to know some tricks of the trade
for QC
-No scattered radiation and photon counting
result in high image quality at half the
radiation dose
-Future possibilities with spectral imaging
Thank’s!
33