J

NASA CASE NO. LAR_15_

PRINT FIG.

NOTICE

The invention disclosed in this document resulted from research in aeronautical

and space activities performed under programs of the National Aeronautics and Space

Administration. The invention is owned by NASA and is, therefore, available for

licensing in accordance with the patent licensing regulations applicable to U.S.

Government-owned inventions (37 CFR 404.1 st seq.).

To encourage commercial utilization of NASA-owned inventions, it is NASA

policy to grant licenses to commercial concerns. Although NASA encourages

nonexclusive licensing to promote competition and achieve the widest possible

utilization, NASA will provide the necessary incentive to the licensee to achieve early

practical application of the invention.

Address informational requests for this invention to the Technology

Applications Team, NASA Langley Research Center, Code 200, Hampton, Virginia

23681-0001.

Address applications for license to the Patent Counsel Office, Mail Stop 212,

3 Langley Boulevard, Hampton, Virginia 23681-0001.

Serial No.: 08/601,143

Filed" 01/26/96 LaRC

LAR 15059-1 -1- PATENT APPLICATION

DIGITAL MAMMOGRAPHY WITH A MOSAIC OF CCD-ARRAYS

Origin of the Invention

The invention described herein was made by an employee of the U.S.

Government and may be manufactured and used by or for the Government for

governmental purposes without the payment of any royalties thereon or therefor.

10

Background of the Invention

1. Technical Field of the invention

15

The present invention relates generally to a mammography device and method

and more particularly to a novel digital mammography device and method to detect

microcalcifications of precancerous tissue.

2. Description of the related art

Diagnostic criteria require that mammograms exhibit excellent spatial

20 resolution and contrast sensitivity. X-ray mammography is currently performed by

using a conventional phosphor screen film combination as the image receptor.

Properly exposed film mammograms can reveal dense precancerous tissue. However,

the size of the smallest detectable calcifications, which are indicative of malignancy, is

typically about 0.2 mm.

25 An imaging system which offers wider dynamic range, higher contrast

sensitivity, higher spatial resolution, and the ability to manipulate and archive the image

is desirable. Digital x-ray mammography can provide the solution to this problem by

providing an advanced method and device for diagnosing minimal breast cancers. This

digital system can allow for precise identification of microcalcifications, the tiny

30 hardenings typically 0.1 to 0.2 mm in diameter found in precancerous breast tissue.
LAR 15059-1 -2- PATENT APPLICATION

The large image size (typically 18 x 24 cm for clinical mammography) could, in

principle, be achieved with grazing-incidence-reflection imaging systems in conjunction

with existing small-area imaging array detectors. However their bulk and enormous

cost make them unsuitable for clinical mammography applications.

5 Two approaches are currently under investigation for digital mammography.

One is the secondary digitization technique, in which conventional film mammograms

are digitized. The other approach is the acquisition of primary digital images, the

"electronic imaging technique". There are numerous studies addressing the technical

challenges of digital radiography which may be adapted for mammography, examples

10 are: scanning laser stimulated luminescence system, i.e., computed radiography (J.W.

Oestmann, D. Kopans, and D.A. Hall, "A comparison of digitized storage phosphors

and conventional mammography in the detection of malignant microcalcifications,"

Invest. Radiol., vol. 23, no. 725, 1988); slot scanning digital imaging, including the

TDI technique (Maidment et al., "Scanned-slot mammography," SPIE Proc., vol.

15 1231, Medical Imaging IV: Image Formation, p. 316, 1990); large size flat panel

detectors such as amorphous silicon and selenium detectors (Rowlands, et al., "X-Ray

imaging using amorphous selenium: A photoinduced discharge readout method for

digital mammography," Med. Phys., vol. 18, pp. 421-431, 1991); and optically coupled

electronic imager (e.g., CCD) techniques (H. Liu, A. Karellas, S.C. Moore, and L.J.

20 Harris, "Lesion detectability considerations for an optically coupled CCD x-ray

imaging system," IEEE Trans. Nucl. Sci., vol. 41, no. 4, pp. 1506-1509, August

1994).

In U.S. Pat. No. 5,105,087, issued to Jagielinski, incorporated by reference

herein, multiple detector arrays are used to image over the large area needed in clinical

25 mammography applications. This invention relies on multiple layers of detector

elements, one above the other, to provide a complete image with no gaps. One

disadvantage with this system is that enough photo detectors must be used to cover the

active area which increases the cost of the device. Another disadvantage is the effect

of the edges of the detector arrays in one layer on the x-ray image seen by the

30 detectors below these edges. The present invention is able to use a fewer number of
LAR 15059-1 -3- PATENT APPLICATION

detectors by repositioning the detectors several times in order to cover the entire active

area. Thus, the cost of the system is greatly reduced.

In U.S. Pat. No. 5,043,582 issued to Cox et al., incorporated by reference

herein, the photo sensitive properties of transistors found in dynamic random access

5 memory (DRAM) integrated circuits are used to detect photons emitted from x-ray

sensitive phosphors. The use of DRAM cells as photo sensitive pixels results in less

optical sensitivity, because the entire active area of each pixel is not photo sensitive,

due to the requirements for addressing the DRAM cells. Furthermore, the detection

scheme described by Cox et al. is binary in nature. Therefore, substantial effort would

10 be required to obtain gray scales.

The present invention uses CCD detectors, which are optimized for use as

photo detectors. This results in greater system sensitivity and image quality. Also,

CCDs produce gray scales naturally and with high sensitivity.

Optically coupled CCD techniques are described in two U.S. Patents. In U.S.

15 Pat. Nos. 5,142,557 issued to Toker et al., and 5,216,250 issued to Pellegrino et al.,

incorporated by reference herein, an optical lens is used to image the visible photons

emitted by an x-ray sensitive phosphor screen onto a single CCD detector. Because

the CCD detector is smaller than the phosphor screen, the image from the screen must

be reduced, or demagnified, in order for the detector to record the entire image. This

20 means that each pixel on the CCD detector corresponds to a larger equivalent area on

the phosphor screen. Therefore, the spatial resolution of this system is less than the

spatial resolution of the CCD detector. Also, using an optical lens to couple the image

on the phosphor screen to the CCD detector is inefficient. The optical lens cannot

collect all of the light that is emitted by the phosphor screen. This results in a

25 reduction in signal-to-noise performance.

The present invention is able to achieve an increased spatial resolution because

each region on the phosphor screen corresponds to a pixel area on the CCD. In

addition, the present invention does not use an optical lens. Therefore, the coupling

losses associated with imaging optics are eliminated. This results in higher quality

30 images and less patient dose of x-rays compared to alternate approaches.
LAR 15059-1

Summary of the Invention

-4- PATENT APPLICATION

10

15

20

25

An object of this invention is to provide a digital mammography device with

large field coverage.

Another object of this invention is to provide a digital mammography device

with high spatial resolution.

Another object of this invention is to provide a digital mammography device

with scatter rejection.

Another object of this invention is to provide a digital mammography device

with excellent contrast characteristics and lesion detectability under clinical conditions.

Another object of this invention is to provide a mammography device which

shields the patient from excessive radiation.

Another object of this invention is to provide a mammography device which

can detect extremely small calcifications.

Another object of this invention is to provide a mammography device which

can manipulate and archive the image.

These and other objects of the invention are met by providing an apparatus and

method for large field digital mammography. The invention uses a mosaic of

electronic digital imaging arrays to scan an image. The imaging arrays are mounted on

a carrier platform to form a pattern. The arrays are then exposed to a portion of a

radiated image, and convert this radiation into digital data. The platform is

subsequently repositioned and the arrays are exposed to another portion of the image.

While the arrays are being repositioned, the digital data in the arrays is transferred to a

computer memory. This process is repeated until the entire image has been exposed to

the arrays. The stored multiple image data is combined by a data processor to form

data which corresponds to the original radiated image. This digital x-ray image can

then be viewed on a computer display. To reduce exposure and x-ray scatter, a

metallic aperture plate is interposed between the x-ray source and the patient. The

aperture plate has a mosaic of square holes in alignment with the imaging array pattern.
LAR 15059-I -5- PATENT APPLICATION

The plate is repositioned in synchronism with the carrier platform. The device is

suitable for incorporation into standard mammography units.

I0

Brief Description of the Drawings

Fig. 1 shows a schematic description of the mammographic system;

Fig. 2a shows a CCD mosaic;

Fig. 2b shows a CCD imager with phosphor and fiber bundle;

Fig. 3 shows arrangement of CCD arrays on the platform where i', j' denote

CCD arrays and i", j" denote sub-images acquired by CCD arrays in various positions;

and

Figs. 4 through 7 show the positions of the arrays which are needed to convert

the entire x-ray into digital data.

15 Detailed Description of the Invention

Referring now to Fig. 1, the mammography system is shown generally by

number 1. X-ray tube 2 emits x-rays 3 through the aperture plate 4 then through the

patient 5. Aperture plate 4 serves to decrease patient x-ray dose and to reduce

20 scattering of the x-ray beam. A phosphorescent screen 6 converts the x-ray image into

a visible light image. Optical fibers 7, which attach the phosphorescent screen 6 to the

CCD arrays, then transmit the visible light image to a mosaic of CCD arrays 8, which

converts the light image into digital data. The CCD/readout electronics subsystem 10,

some of which are located directly on the platform 16 and some of which are located

25 externally, are used to transfer this data into a personal computer 11 for storage. A

mechanical repositioning stage 9 moves the mosaic of CCD arrays to a new position,

and this process is repeated until the entire image is exposed. The personal computer

11 combines this data to produce data which corresponds to the entire x-ray image.

This x-ray image is displayed on an image display 12. Repositioning stage 9 is driven

30 by the CCD mosaic repositioning stage electronics 13, under the control of the
LAR 15059-1 -6- PATENT APPLICATION

personal computer 1I. The aperture plate repositioning stage electronics 14 moves the

aperture plate 4 in synchronism with the CCD repositioning stage 9, also under control

of the personal computer ] 1.

Sensor means

5 Referring now to Figs. 2a and 2b, CCD mosaic 8 consists of CCD arrays 15

mounted onto a carrier platform 16. Fig. 3 shows that the length 22 between

neighboring arrays is equal to the length 23 of one side of a square array. However,

the arrays can have any shape and length so long as they are separated by a distance

equal to the dimension of the arrays along each axis of motion minus an allowance for

10 overlap of approximately 10 pixels between sub-images generated by each CCD in

both directions. With this detector geometry, a single x-ray exposure will result in an

image with gaps. These gaps in the image are removed by using multiple x-ray

exposures. After each exposure, the platform 16 which carries the mosaic 8 of CCD

arrays 15 is rapidly and accurately repositioned with respect to the patient 5 along two

15 orthogonal axes. The repositioning can be accomplished with commercial mechanical

stages.

The mosaic 8 is repositioned rapidly in order to minimize the effects of patient

movement between exposures. The movement of the mosaic 8 is facilitated by the

presence of an x-ray transparent plastic spacer plate 17 located between the patient 5

20 and the surface of the CCD mosaic 8.

Forty-eight 1024 x 1024 pixel CCD arrays, each measuring 15 mm x 15 mm,

are fixed to a 24 cm wide by 18 cm high carrier platform. Fig. 3 shows that the length

22 between neighboring arrays is equal to the length 23 of one side of a square array.

However, the arrays can have any shape and length, so long as they are separated by a

25 distance equal to the dimension &the arrays along each axis of motion minus an

allowance for overlap of approximately 10 pixels between sub-images generated by

each CCD in both directions.

In order to provide a complete and contiguous image, the mosaic 8 is

repositioned three times, as shown in Figs 4 through 7. Four x-ray exposures are

30 made. Aider the first exposure, the mosaic 8 is moved along the x axis a length 22,
LAR 15059-1 -7- PATENT APPLICATION

then a second exposure is made. The mosaic 8 is then moved along the y axis by a

length 22, followed by a third exposure. The mosaic is then moved along x axis in a

direction opposite the first motion. A final exposure then completes the data

acquisition sequence.

5 In an alternate embodiment, the detector mosaic has 48 individual CCD arrays

are assembled into a 6 x 8 mosaic with less than 5 mm wide gaps (where the gap width

is W) between the individual CCD arrays. The repositioning takes place along a

diagonal direction of the array. After a first x-ray exposure, the entire mosaic of CCD

arrays is mechanically repositioned with respect to the human subject to be imaged.

10 The mosaic is first moved in a diagonal direction by v/2 W mm (simultaneously, W

mm upward and W mm sideways). Then a second exposure is made followed by a

second movement of the detectors along the same diagonal direction. A third

exposure completes the data acquisition sequence. As in the preferred embodiment,

the aperture shield is moved in synchronism with the mosaic of CCD arrays.

15 Shielding means

These multiple x-ray exposures can result in a high dose of radiation to the

patient. In order to reduce the amount of x-ray exposure and scatter, a metal aperture

plate 18 as shown in Fig. 2a is interposed between the x-ray source 2 and the patient 5.

The plate 18 has a mosaic of apertures 19 which are in exact alignment with the mosaic

20 8 of detector arrays 15. This aperture plate 18 is moved by a second repositioning

device in synchronism with the mosaic 8 detector arrays 15.

The patient 5 receives a small amount of additional exposure from x-rays in a

narrow borderline area that surrounds each array. However, appropriate configuring

of the instrument allows this area to be kept to less than 7.5 percent. Thus, patient

25 dosage is increased by this percentage.

Scatter Reduction

The aperture plate provides a significant reduction in x-ray scattering, which

results in improved image contrast. Table 1 shows scatter as a function of

compression and Bucky grid use based on 15 - 20 keV x-ray properties. The
LAR 15059-1 -8- PATENT APPLICATION

instrument configuration for the CCD mosaic technique allows easy adaptation of a

screen film type Bucky grid subsystem for scatter control.

Table 1

S/P values

5 With Bucky Grid

3.0cm Compression

Screen Film: 0.14

This device: 0.05

4.5cm Compression

Screen Film: 0.26

This device: 0.09

10

W/O Bucky Grid Screen Film: 0.40

This device: 0.14

Screen Film: 0.75

This device: 0.27

Scatter reduction yields better contrast ratios and thus enhanced lesion

detectability. For a performance comparison consider Bucky grid equipped film

systems. With 3 cm breast compression they typically are capable of a Scatter to

15 Primary (S/P) ratio in the range from 0.10 to 0.15. For the present invention, the

Table shows a comparable S/P ratio of 0.14 for 3 cm compression without a grid.

However, this system has a dose penalty of just under 7.5 percent, as a result of

border line area considerations discussed above, compared with an approximately 100

percent dose increase required for the Bucky grid which is generally used by film

20 systems. A trade off analysis which considers contrast shows that the present

invention can achieve identical lesion detectability with 45 to 50 percent less radiation

dosage, depending on compression. This result clearly shows the advantage of the

present invention, which can operate without a Bucky grid because of the inherent

scatter rejection of the aperture plate.

25 Repositioning means

The synchronous repositioning of the mosaic 8 of detectors 15 and aperture

plate 18 is accomplished with two separate 2 axis mechanical repositioning devices

with electronic coupling, such as the 800000 series precision positioning stage from

Parker Hannifin. Stage movement of the repositioning devices is controlled by a

30 Computermotor Plus closed loop brushless servo-motor system from Parker Hannifin.
LAR 15059-1 -9- PATENT APPLICATION

A step-motor system may also be used. Direct access programming allows the user to

adjust all parameters via the RS232 interface.

Appropriate phasing of the independent motions of the detector mosaic 8 and

the aperture plate ]8 ameliorates mechanical vibrations to the instrument. One method

5 &reducing vibrations is to move the aperture plate 18 in the direction opposite to the

motion of"the detector mosaic 8.

Exposure means

Each CCD array 15 in the mosaic 8 is coupled to the x-ray image 3 by using a

phosphor screen 20 which converts the x-ray image into visible light. As shown in Fig.

10 2b, the screen 20 is separated from the CCD array ]5 by a fiber optic bundle 2] with

unity magnification. The main purpose of the fiber optic bundle 21 is to absorb a

majority of the x-rays that are not stopped by the scintillating screen 20. This will

prevent noise problems which result from x-rays contacting the CCD arrays. This

unity magnification of the bundle 21 will avoid contrast degradation that is usually

15 associated with an optical fiber taper.

Data Transfer means and Data storage means

In the time period between the radiation exposures, while the mosaic of

detectors is being repositioned, the data is transferred from the CCD arrays 15 into the

personal computer l 1. When a data clocking speed of 1.5 million pixels per second is

20 used, approximately 280 milliseconds will be required to transfer the data from the

pixels into computer memory.

The transfer of the image data from the CCD arrays 15 to a data storage means

such as a standard personal computer (PC) l l can be accomplished through a process

called binning. The scintillator screen resolution of 16-18 iine-pairs/mm will be the

25 limit of the overall system spatial resolution. The available CCD pixel size of 15 by 15

microns is much larger than needed to match the screen resolution. Therefore, the

output of four adjacent pixels (2 by 2 pixels) can be simultaneously clocked and

electronically combined without any degradation of the system resolution.
LAR 15059-1 -I0- PATENT APPLICATION

This binning of data offers several important advantages. First, if one of the

four adjacent CCD array pixels is defective, binning can still deliver an image without

drop out. Thus, lower grade and less expensive CCD arrays can be used.

Second, binning reduces the required total computer memory. This is a major

5 point, because even with binning, recording a complete 18 cm by 24 cm image

presently requires 75 Mbytes. An additional 25 Mbytes of memory will be needed for

data processing, image manipulation, and system management. Much of this data can

be swapped from hard disk or other permanent storage medium.

Third, binning reduces the information transfer time. Binning is partly

I0 accomplished in analog fashion by performing two parallel transfers prior to each

readout of the serial register of the CCD. This allows the required CCD readout time

to be reduced by one half.

Short read out times are crucial in order to minimize the image blurring effects

of patient motion. The CCD contents from each of the first three exposures is read

15 into computer memory coincident in time with each of the corresponding three

detector repositioning times that follow exposure.

A readout rate is chosen for parallel and serial binned pixe]s. The upper and

lower serial registers and read out amplifiers available with the Loral Inc., CCD are

used. The rate is set at less than the maximum rate available for this CCD in order to

20 improve the CCD charge transfer efficiency and the CCD amplifier read noise. The

requirements on the CCD parallel register drivers, which are adversely affected by

capacitive loading at high clock rates are also relaxed. This approach requires an

additional analog to digital converter and its electronics for each CCD.

Data Combining means (Image Reconstruction)

25 The software manipulations needed to reconstruct a seamless image require

two steps. First, a simple coordinate repositioning of the stored data is done in order

to translate the stored data which was generated after each exposure by the distance

the CCD arrays had been moved prior to each exposure.

Second, a linear scale factor correction method for pixel to pixel response and

30 radiation source intensity variations is performed. A linear scale factor data array is
LAR 15059-1

10

15

-11- PATENT APPLICATION

derived using reference image information. A reference image is generated and

recorded by the same image producing method described above. A correction data

array is then created by dividing the output of each individual pixe] by the output

average of the entire array. For all subsequent testing, the raw images are normalized

using this linear scale factor data array.

Image reconstruction

Image acquisition/Processing Procedure

]. Obtain Offset/Dark Current Subtraction Values

a. Simultaneously and independently integrate all CCD arrays

under dark conditions for time 17i. Store results for array at

position i', j' in array variables DAi," j, k, I, where k, I are indices

of pixels on each array.

b. Obtain new dark exposure for each array and store results as

DS_,, j,, _

c. Update running total of dark exposure data:

DAi,,j,, k, i = DAi, j,, k, 1+ DSi,,j,, k, 1

d. Repeat steps b and c N d more times - N d typically ranges from 5

-10

e. Compute average dark level for each array:

_ DA,_,/, k, t

DAt_,/, k, t (Na+2)

20

25

. Obtain

a.

b.

Non-Uniformity Correction Values

Simultaneously and independently integrate all CCD arrays

under exposure from clinical x-ray source with no subject

present for time "I_i at a dose that produces a spatially uniform (<_

2% variation) signal level of 80% - 90% of pixel full well

capacity. Store results in array variables RAq, j, _ l

Obtain new exposure under same conditions and store results as
LAR 15059-1

C.

d.

e.

-12- PATENT APPLICATION

RSi', j', k, l

Update running total of non-uniformity correction data:

RAi',j',k,I=RAi',j'k,I+RSi',j' k,l

Repeat steps b and c N r more times - N r typically ranges from

15 - 30

Compute average non-uniformity response of each array:

RAi(]/, k, l

RAi/,jl, k, l

(N+2)

10

f

g.

Compute difference frame between dark and exposed response

for each array:

RAi, j, k,i = DAi, j, k, 1- RAi,,j, k, 1

Compute average response of all arrays:

/ZI D

M N Np_-i Np,x-i

 ZZZ Z

i/=l j/=l k=0 /=0

2

(N;,x)(MN)

where Npi x = the number of array pixels in each dimension

h. Compute correction factor arrays:

2

= )

CORRj/,/, k. t (RAi,. j,, k, l

15

,

i. Clear variables RSi,,j,, k, t; Rmi,,j,, k, i; and DSi, j,, k,l.

Acquire Clinical Image

a. Position subject between mosaic and x-ray source

b. Simultaneously and independently integrate all CCD arrays for

time "t"i with appropriate clinical x-ray dose. Store results for

each sub-image in array variables PVli,,j," k, 1" (See figure 4)
LAR 15059-1

10

15

4

2O

C.

d.

e.

£

g.

h.

-13- PATENT APPLICATION

During readout in step b, translate mosaic and aperture shield

such that an exposure can be acquired at position indicated by

figure 5. Maintain approximately 10 pixels at overlap between

exposures from sub-image to sub-image in each direction

Acquire second exposure and store results in array variables

PV2_,, j, k, 1

Translate a mosaic and aperture plate to allow acquisition of

sub-image in position indicated by figure 6.

Acquire third exposure and store results in array variables PV3i."

j', k, I

Translate mosaic and aperture plate to allow acquisition at subimage in position indicated by figure 7.

Acquire fourth exposure and store results in array variables

PV4i', j', k, I

Process Data and Reconstruct Image

a. Correct sub-image data for dark response and non-uniformity:

PVli', j', k, 1 = CORRi', j', k, I (DAi', j', L 1 - PVli', j', k, 1)

PV2i', j', k, I = CORRi', j', k,I (DAi', j', L I- PV2i', j', k, l)

PV3i',j', k, l = CORR,, j,, k, I (DA4',j', k, 1- PV3i',j', k, l)

PV4i', j', k, 1= CORRi', j', k, I (DAg, j', k, I - PV4i', j', k, 1)

b. Initialize sub-image counters:

i'= 1;j'=l

c. Compute reconstructed image pixel values and store in array PV

2i/-2 2j'/-2

PV(k/+ _ N%., l:+ _ Ny.,) : PVI,,j,._,.,,

i:/-O j//=O _'

25
LAR 15059-1 -14- PATENT APPLICATION

2i/-1

PV(k/+ _ Nx.,

i//=0

2J/-2

t'+Z _,) =vv2,,_,,,,,

j//:O

2i/-1 2j/-I

vv(k'+Z N,,,,t'+Z N) =VV4,,j,,,,,

i//:0 j//:0

2t / 2 2j/-I

w_,ereNo- O,NogV6_'+Z N, t'+Z N) : VV3,,_,,,,,

i//:O j// 0

d.

e.

f.

For purposes of the preceding steps,

N

k / : k - ovx

2

for _ <_ k -< pN-ix -

2

Increment i' by 1 until i' = M

Increment j' by 1 until j' = N

Display image array PV using appropriate gray scales

N

OVX

2

N

l / = ! - ow

2

N Now

for w° <_ l <_ Npix - -- 2 2
LAR 15059-1 -15- PATENT APPLICATION

Now- the approximate number ofpixels overlap in sub-images in the X direction

between exposures

Now- the approximate number ofpixels overlap in sub-images in the y direction

between exposures

N - the size of the pixel offset along the X direction between sub-images at

positions i" and i" + 1, for the CCD sub-region defined by:

N N

o,,x <_ k <_ N - o_x

2 ovx 2

N"y Now _ i._ N _

2 ow 2

10

between positions described in figures 4 and 5 for sub-image at index i"

NvM- the size of the pixel offset along the Y direction between sub-images at

-j

positions j" and j" + 1, for the CCD sub-region defined by:

Now N

<_ k <_N - ovx

2 o_ 2

N N

ow _ l -< N _ ow

2 ow 2

15

between positions described in figures 5 and 6 for sub-image at index j"

Offsets Nx/' and %, are obtained by taking the test image incorporating

grid lines crossing boundaries between all sub-images along directions orthogonal to

boundary and adjusting values until r.m.s, difference between cross sections on both

sides of the boundaries are minimized.

Aperture sizes on aperture shield shall be set to produce 5 - 10% overlap in

illuminated regions along each linear dimension between sub-images. This process

assumes that all CCD's have the same rotational orientation to within A0_<

N.

where AO is the angle of rotation, p,x
LAR 15059-1 -16- PATENT APPLICATION

While preferred embodiments have been described in detail, numerous

modifications and changes may be made within the principles of the invention which is

to be limited only by the appended claims.

What is claimed is:
"Page missing from available version"
LAR 15059-1 -23- PATENT APPLICATION

DIGITAL MAMMOGRAPHY WITH A MOSAIC OF CCD-ARRAYS

Abstract of the Disclosure

5 A digital mammography device uses a mosaic of electronic digital imaging

arrays to scan an x-ray image. The mosaic of arrays is repositioned several times to

expose different portions of the image, until the entire image is scanned. The data

generated by the arrays during each exposure is stored in a computer. After the final

exposure, the computer combines data of the several partial images to produce a

10 composite of the original x-ray image. An aperture plate is used to reduce scatter and

the overall exposure of the patient to x-rays.
Ol-()'.i '_JJ_., (,_,: !4 _J04 _,,64 -?509 PATENT COUNSEL

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j"=2N j'=N

j"=5 j'=3

ll_4

j"=3 j'=2

j IJ.._ 2

23 22

j"=l j'=l

il=l

il=2

i'=3 ....... i'=M

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Fig. 3