Technical evaluation of Fujifilm AMULET Innovality digital mammography system

39 Pages·2017·1.23 MB·English

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NHS Breast Screening Programme
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Equipment Report 1601 d
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Technical evaluation of Fujifilm (AMULET
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Innovality digital mammography system
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Public Health England leads the NHS Screening Programmes

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Technical evaluation of Fujifilm AMULET Innovality digital mammography system
About Public Health England

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Public Health England exists to protect and improve the nation's health and wellbeing, r
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and reduce health inequalities. It does this through world-class science, knowledge and n
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PHE is an operationally autonomous executive agency of the Department of Health.

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About PHE Screening r N
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Screening identifies apparently healthy people who may obe at increyased risk of a disease
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or condition, enabling earlier treatment or better informed decisions. National population
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screening programmes are implemented in the NHS on the advice of the UK National
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Screening Committee (UK NSC), which makes independent, evidence-based
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www.gov.uk/topic/populationh-screening-Mprogrammes
Twitter: @PHE_Screeningt Blog: phescreening.blog.gov.uk

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Prepared by: CJ Strudley, JM O duko, KC Young
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For queries relatring to this dcocument, please contact: [email protected]
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The image on page 8 is ciourtesy of Fujifilm.
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© Crown copyright 20y17
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fPublished February 2017
PHE publications gateway number: 2016633

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Technical evaluation of Fujifilm AMULET Innovality digital mammography system
About this document

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Acknowledgements r
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The authors are grateful to the staff at the Breast Unit at Barnsley Hospital, for their e
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cooperation in the evaluation of the system at their site.

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Document lnformation t P
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Technical evaluation of Fujifilm
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Title d
AMULET Innovality digital
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mammograpohy system
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Policy/document type Equipment Report 1601
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Electronic publication date aFebruary 20a17
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Version i 1
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Superseded publicatio ns None
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Review date t None

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Author/s CJ Strudley, JM Oduko, KC Young
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Olwner y NHS Breast Screening Programme
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i Docu ment objective To provide an evaluation of this
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v (chlinical/healthcare/social equipment’s suitability for use within
A tquestions covered) the NHSBSP

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Population affected Women eligible for routine and higher-
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risk breast screening
Target audience Physicists, radiographers, radiologists
Date archived Current
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Technical evaluation of Fujifilm AMULET Innovality digital mammography system
Contents

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About Public Health England 2 r
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About PHE Screening 2
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Executive summary C 5

1. Introduction g 6
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1.1 Testing procedures and performance standards for digital mammography 6
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1.2 Objectives a 6
2. Method n C 6
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2.1 System tested d 6
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2.2 Output and HVL o 7
2.3 Detector response - ( 8

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2.4 Dose measurement 9
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2.5 Contrast-to-noise ratio 9
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2.6 AEC performance for local dense areasa l a 11
2.7 Noise analysis n r 12
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2.8 Image quality measurements o 13
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2.9 Physical measurements of the dietector performance 15
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2.10 Optimisation 15
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2.11 Other tests 16

3. Results e a 16
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3.1 Output and HVL 16
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3.2 Detector respon se f 17
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3.3 AEC performance 17

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3.4 Noise measurementss 23
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3.5 Imagef quality measurements 24
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3.6 Comeparison wisth other systems 25
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3.7 bDetector performance 29
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3.8 a OptimisPation 31
i3l.9 Othe r tests 33
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4. Discussion 35
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A 5. Cotnclusion 37

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Reoferences 38
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Technical evaluation of Fujifilm AMULET Innovality digital mammography system
Executive summary

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The purpose of the evaluation was to determine whether the Fujifilm AMULET r
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Innovality meets the main standards in the NHS Breast Screening Programme n
(NHSBSP) and European protocols, and to provide performance data for comparison e
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against other systems.

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For use in the NHSBSP, it is recommended that the system is operated with the )
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automatic exposure control (AEC) in iAEC mode at dose setting H (High). This allows
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image quality to approach or exceed the achievable level of image qualaity at all breast
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thicknesses. Operation at dose setting N (Normal) gives achievable inmage quality only
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for equivalent breast thicknesses up to 60mm. Operation at dosed setting L (Low) is not
recommended, as the image quality is then below the NHSBSPr and EuropNean
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standards. (
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The dose to the standard breast was 1.48mGy at doseC setting H, hwell below the dose
limit of 2.5mGy. p
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Technical evaluation of Fujifilm AMULET Innovality digital mammography system
1. Introduction

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1.1 Testing procedures and performance standards for digital mammographyr
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This report is one of a series evaluating commercially available direct digital radiography
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(DR) systems for mammography on behalf of the NHS Breast Screening Programme

(NHSBSP). The testing methods and standards applied are mainly derived fromg
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NHSBSP Equipment Report 06041 which is referred to in this document as ‘thne M
NHSBSP protocol’. The standards for image quality and dose are the samie as those
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provided in the European protocol,2,3 but the latter has been followed where it provides
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a more detailed standard, for example, for the automatic exposure control (AEC)
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system.
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Some additional tests were carried out according to the UK recommend(ations for testing
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mammography X-ray equipment, as described in IPEM Roeport 89.4 y
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1.2 Objectives
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The aims of the evaluation were: g
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• to determine whether the Fujifilm AMtULET Innomvality digital mammography system
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meets the main standards in the NNHSBSP amnd European protocols

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• to provide performance datae for comparison against other systems
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2. Method s
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2.1 Sybstem teshted
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Thei tests were conducted at the Breast Unit at Barnsley Hospital, on a Fujifilm AMULET
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vInnovality hsystem as described in Table 1. All tests in this report were carried out using
A the “QCt Test” image format (manufacturer’s parameters: Max 4.0 mammo, S=121, L=4)

The Irnnovality system is shown in Figure 1.
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Technical evaluation of Fujifilm AMULET Innovality digital mammography system
Table 1. System description
Manufacturer Fujifilm
Model AMULET Innovality

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Target material Tungsten
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Added filtration Rhodium t
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Detector type Amorphous selenium
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Detector serial number J125020 C
Image pixel size 50µm
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Detector pixel size Hexagonal pixels with an area equivalent
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to that of a 68µm square pixel i
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Detector size 240mm x 300mm a
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Pixel array 4728 x 5928
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Pixel value relationship to Logarithmic d
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dose
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Source to detector distance 650mm - (

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Source to table distance 633mm
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Automatic exposure control AEC, iAEC
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(AEC) modes al a
Software version FDR-3000AWnS Mainsoft Vr5.1
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Two AEC modes are available for use wtith the Innomvality: AEC and iAEC.
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Both modes can operate at three different dose settings: N (Normal), L (Low) and H

(High). Exposures under both AEC modes aare determined by a pre-exposure, which
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does not contribute to the imhage and is eMxcluded from the mAs shown for the image.
The kV and mAs for the prte-exposur e are recorded separately in the DICOM header for

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the image. o

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iAEC uses all the pixel data from the detector in the pre-exposure to calculate the breast
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area, breast co mposition i(dense, fatty, implant) and dense area position. The
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appropriate exposure factors (kV and mAs) are determined from this information.
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The AEaC mode isP similar to the original AMULET’s AEC. It uses the pixel values from
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regiions at a fix ed distance from the chest wall edge (CWE) to calculate the exposure.
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The AEC mode was intended for use in quality control (QC) tests, in case there was
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A variation in how the PMMA was set up. However, the iAEC mode used with PMMA was
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foundr by the manufacturer to give a stable and consistent result so the AEC mode need
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not be used for QC.
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2.2 Output and HVL
The output and half-value-layer (HVL) were measured as described in the NHSBSP
protocol, at intervals of 3kV.
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Technical evaluation of Fujifilm AMULET Innovality digital mammography system

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Figure 1. Thee Fujifilm AsMULET Innovality
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2.3i Detect or response
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The dettector response was measured as described in the NHSBSP protocol, with a

45mmr block of polymethyl-methacrylate (PMMA) at the tube head. An ion chamber was
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positioned above the table, 40mm from the CWE. The incident air kerma was measured
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at the detector surface for a range of manually set mAs values at 29kV. The readings
were corrected to the surface of the detector using the inverse square law. No
correction was made for attenuation by the table and detector cover. Images acquired at
the same mAs values were saved as unprocessed files. They were transferred to
another computer for analysis. A 10mm square region of interest (ROI) was positioned
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Technical evaluation of Fujifilm AMULET Innovality digital mammography system
on the midline, 40mm from the CWE of each image. The average pixel value and the
standard deviation of pixel values within that region were measured. The relationship
between average pixel values and the detector entrance surface air kerma was

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determined.
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2.4 Dose measurement
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Doses were measured using the X-ray set’s AEC in the iAEC mode to expose different

thicknesses of PMMA. All three dose settings, N, L and H, were used for these g
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measurements. Each PMMA block had an area of 180mm x 240mm. Spacers were
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used to adjust the paddle height to be equal to the equivalent breast thicktness, as P
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shown in Table 3. The exposure factors were noted and mean glandular doses (MCGDs)
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were calculated for equivalent breast thicknesses. i C
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An aluminium square, 10mm x 10mm and 0.2mm thick, was uosed with the PMMA
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during these exposures, so that the images produced could- be used for the calculation

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of the contrast-to-noise ratio (CNR), described in Section 2.5. The aluminium square
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was placed between two 10mm thick slabs of 180mm x 240mm PMMA, on the midline,
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with its centre 60mm from the CWE. Additional laaylers of PMMaA were placed on top to
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2.5 Contrast-to-noise ratio i
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Unprocessed images acquired during the dose measurement were downloaded and

analysed to obtain the CNRs. Thirty six smaall square ROIs (approximately 2.5mm x
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2.5mm) were used to determhine the averMage signal and the standard deviation in the
signal within the image of tthe alumin ium square (4 ROIs) and the surrounding

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background (32 ROIs), as shown ion Figure 2. Small ROIs are used to minimise
distortions due to thoe heel effec t and other causes of non-uniformity.5 However,
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because a flat-fierld correctiocn is applied, this is less important for DR systems than in
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computed rad iography syistems. After correcting the pixel values to achieve a linear
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relationship between pyixel value and dose, the CNR was calculated for each image, as
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defined in the NHSBSP and European Protocols.
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Figure 2. Location and size of ROI used to determine the CNR
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To apply the standards in the European protocol, it is necessary to relate the image
quality measured using the CDMAM (Section 2.8) for an equivalent breast thickness of
60mm, to that for other breast thicknesses. The European protocol2 gives the

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relationship between threshold contrast and CNR measurements, enabling the
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calculation of a target CNR value for a particular level of image quality. This can be t
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compared to CNR measurements made at other breast thicknesses. Contrast for a
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particular gold thickness is calculated using Equation 1, and target CNR is calculated
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using Equation 2.

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Contrast = 1 − e-µt n (1) M
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where µ is the effective attenuation coefficient for gold, and t is the gold thickness.
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(cid:18)(cid:19)(cid:20) × (cid:30)(cid:18) i C
CNR = (cid:21)(cid:22)(cid:23)(cid:24)(cid:25)(cid:26)(cid:22)(cid:27) (cid:21)(cid:22)(cid:23)(cid:24)(cid:25)(cid:26)(cid:22)(cid:27) d (2)
(cid:13)(cid:14)(cid:15)(cid:16)(cid:17)(cid:13)
(cid:30)(cid:18)(cid:31)(cid:23)(cid:26) (cid:22)(cid:31) r N
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where CNR is the CNR for a 60mm equivalent breast, TC is the threshold
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contrast calculated using the threshold gold thickness fCor a 0.1mmh diameter detail,
(measured using the CDMAM at the same dose as used for CNpR ), and TC
measured target
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is the calculated threshold contrast correspondinag to the threashold gold thickness
required to meet either the minimum acceptabnle or achievrable level of image quality as
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defined in the UK standard. o
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The 0.1mm detail threshold gold thickness is used here because it is generally regarded
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as the most critical of the detail diameters for which performance standards are set.

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The effective attenuation coehfficient for gMold used in Equation 1 depends on the beam
quality used for the exposutre, and was selected from a table of values summarised in

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Table 2. These values wmere calculoated with 3mm PMMA representing the compression
paddle, using spectora from Boo ne et al.6 and attenuation coefficients for materials in the
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test objects (alumrinium, goldc, PMMA) from Berger et al.7
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The European protocol also defines a limiting value for CNR, which is calculated as a
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percentagbe of the thhreshold contrast for minimum acceptable image quality for each
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thickness. This limPiting value varies with thickness, as shown in Table 3.
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Table 2. Effective attenuation coefficients for gold contrast details in the CDMAM
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kV Target/filter Effective
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attenuation
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(µm-1)
28 W/Rh 0.134
31 W/Rh 0.122
34 W/Rh 0.109

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