Gastrointestinal Examinations with Digital Radiography1

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Mutsumasa Takabasbi, MD #{149} Sukeyosbi Ueno, Shunji Yosbimatsu, MD #{149}Yosbibaru Higasbida, Tadatosbi Tsucbigame, MD #{149} Kosbiro Ito, MD Masafumi Hara, MD #{149}Takao Takada, RT Masami Kamiya, PhD #{149} Akira Yoshida, BSc

Basic

imaging

properties

radiography ;

1,024

system

and

2,048

spots

(0.3

and

layer

of the

without VV

VV

V

matrices,

08

mm)

and

usefulness was

reduced

camera.

of an

upgraded

system,

which

has

upgraded

with

The

thickness

Screen-film of the

upper

digital

and

lower

system,

tract,

digital

were

comparable

grade

of the

better

than

2,048

matrix

especially

images

examination

U

INTRODUCTION

for

processed

in quality system.

for

systems

For

the with

the

lower

digital

images,

except

with

unsharp

masking.

of other

parts

(GD

mission

and

tract,

since

instant

these

image

systems

display

produced

resolution,

presence

Abbreviations: Index

GI

terms:

From

1992;

the

faster

poration

(M.K.), Okayama,

0

RSNA,

6;

final

tract

of Radiology, Science

Kashiwa,

1SF

glare,

=

line

and

spread

Radiography,

digital

#{149}

function,

video

data

Radiography,

=

a 2,048

X

system

warranted.

camera, of the

acquisition

and gastno-

and

trans-

screen-film

capabilities limitations,

MiT

up-

were

of the

conventional

smaller

after

radiogra-

imaging

and low radiation including lower spafields (4-6). Although

modulation

transfer

function

technology

#{149}

12:969-978

Department

of Medical

Sciences, March

gastrointestinal,

Gastrointestinal

RadloGraphlcs

College

=

ofveiling

with

examinations

phy equipment, as well as digital image processing dose (1-3). However, digital systems have crucial tial

and images

intensifier,

with

upper

techniques

evaluation seems

provide

compared

the

before

those

of

a 50%

For

masking screen-film

body

transfer

to those frequency.

system.

Further

of the

(GD

despite

tract,

radiography systems consisting of an image image processor have been used in radiologic

intestinal

spatial similar

images

for

and

modulation

unsharp

GI

(with

comparable

lower

to screen-film

photoconductive

images

Overall

were digital

x focal

gastrointestinal

were

at the

of the two exposure

contrasts in incident

digital 1,024

smaller

of the

and

used in the clinical evaluation. of the upgraded digital system

screen-film

Digital digital

V

x 2,048

postprocessing)

Threshold reduction GI

clinical

evaluated.

video

tract were functions the

and were

MD RT

(Y.H.), Japan;

School

of Medicine

Kumamoto

University,

and

the

Department

Japan (A.Y). From the 1991 revision received May 15; accepted

RSNA May

(MT., 1-Chome, of Radiologic

S.U.,

S.Y.,

T. Tsuchigame,

Honjo,

Kumamoto

Technology,

scientific assembly. 18. Address reprint

Received requests

K.I., 860,

Okayama

M.H.,

Japan;

T. Takada), Hitachi

University

February to MT.

3, 1992;

and

Medical

School revision

the Cor-

of Health requested

1992

969

Resolution

6.5 lp/mm

Contrast

35

size

Output

Saticon

Image

pick-up

tube for

Image

2looscanhines

60 mm

r

Recorder

MD

1GB

OD

600MB

I PASS I

I

Figure

1. Block diagram of the digital radiography system. The output surface of the image intensifier (II) 60 mm in diameter. The video camera has an impregnated diode-gun Saticon (Hitachi Medical) capable of scanning 2, 100 lines. The image processing unit includes the analog-to-digital converter and can process images of 2,048 x 2,048 matrix at one image per second and images of 1,024 x 1,024 matrix at four images per is

second.

Various

image

processing

techniques

on a cathode ray tube (CR0 with 2, 132 scan pairs per millimeter, MB = megabytes, MD communication system.

attempts have been lems (1-4), resolution

currently

used

ventional

screen-film

In 1990, digital 2,048

matrix.

with

a new

with

nominal

is still inferior

to that

of con-

This

system

has

camera and

and

described been an

0.8-mm

a

2,048

x

upgraded x-ray

focal

the upper U

performance

and

with

lower

. Equipment The major components consist of a video with three display

clinical

images

GI tract.

AND

MATERIALS

camera, modes

an image

processor,

METHODS

1). Image

available

sizes

with

1,024

and

image

intensifier. with

2,048

x 2,048

second image

with the is processed

digital

an image (7, 9, and

system intensifier 12 inch),

system

exposures image

one

matrix

for

digital

processing

algorithms,

sharp

stantly

masking displayed

techniques on 1,024

2,048

monitors.

ing

the

Hard

thickness

camera

increase

video

1,024 mode

four

images

x of

the

the

per

matrix. Each by several including

un-

(10, 1 1), and is inx 1,024 or 2,048 x

copies

of images

can

be

are digitally stored. was upgraded by reduc-

of the

of the video the

each

can be accomsecond with

per

and

matrix are

1,024 x 1,024 automatically

printed before they The digital system of our

a laser

acquisition

this x 2,048

2,048

Radiographic

plished

of

two monitors,

and an image file with a large memory (Hitachi Medical, Kashiwa, Japan)

printer, capacity

tube spots

(8,9). In this article, we describe the system, compare the basic imaging properties before and after the system upgrade, and evaluate observer

=

=

(Fig 1, Table

et a! (4,7) a high-resolution

0.3-

=

=

systems.

with video

=

=

made to solve these probof the digital systems

Takahashi

system

are available, including unsharp masking. Images are displayed lines. DR digital radiography, GB gigabytes, lp/mm line magnetic disk, OD optical disk, PACS picture archiving and

photoconductive

from signal

4 m current.

layer

to 2 pm to Nominal

of the focal spots were also changed from 1.0 mm to 0.3 and 0.8 mm (two foci in one tube) to improve the geometric unsharpsizes

ness

970

U

RadioGraphics

U

Takahashi

et a!

of the

system.

Volume

12

Number

5

Table 1 Specifications

ofthe

Digital

System

Radiography

Item Image

intensifier

Video

camera

Specifications

Input size: 7, 9, and 12 inches (three modes) Camera tube: 1-inch impregnated diode-gun Scanning 1,050

capabilities: 2, 100 lines, lines, 15 fps progressive,

lines, Analog-to-digital Imaging mode Image

Image

converter

conversion x 1,024 x 2,048

file

Image

memory:

display

Magnetic disks (four): 330 Mbytes Optical disk (5 inch): 600 Mbytes Monitors (two): 20-inch screen Scanning capabilities: 1,066 and 2,132 Laser printer

Note.-fps

Window frames

=

per

width

and 1,081

for fluoroscopy

10-bit 1,024 2,048

Hard copy Image processing

Table

30 fps interlace,

Saticon

4 fps progressive, for radiography;

at 20 MHz matrix, four images matrix, one image

per second per second

64 Mbytes

and

level,

filtering,

lines,

60 fps

enlarging

second.

2 Parameters

Radiographic

before

and

after

Upgrade

of Imaging

Systems

kV

mA

Exposure Time (msec)

Digital Screen-film After upgrade Digital

85-95 85-95

300 300

50-70 50-70

115 105

1.0 1.0

1.0* 1.0

85-95

100

Screen-film

85-95

300

50-60 60-75

115 105

0.3 0.8

0.5 1.0

System

Before

source incident =

Measured

to image exposure:

.

S:ThJ,

Konica

Medical,

Tokyo;

Radiographic

parameters

1992

are

shown

of Basic

Imaging

Line spread functions (LSF5) of the old (1.0-mm) and new (0.3- and 0.8-mm) focal spots were measured from images of a 10-i.m slit.

HR-S

in Table

Measurement

Properties

film, Fuji Medical Systems, Tokyo) placed in front of the image intensifier surface. The distance between the focal spot and the tabletop was 100 cm for both techniques. The distance between the screen-film cassette and the tabletop was 5 cm, compared with 1 5 cm between the image intensifier and the tabletop.

September

Relative Dose

receptor distance. 0.29 X 104C/kg.

Both digital and screen-film examinations were performed with the same remote-contro! unit with an x-ray tube over the table. Screen-film radiography was performed by using a medium-speed screen-film system (SRO 250 rare earth screen [phosphor

Gd2O2

Focal Spot (mm)

upgrade

Note.-SID *

SID (mm)

Modulation transfer functions (MTFs) of focal spots were calculated by means of digital Fourier transformation of the LSFs. Overall MTFs, including focal spots and presampling MTFs (6), which include the unsharpness of

2.

Takahashi

et a!

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RadioGraphics

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971

I .0

>-

I.-

Co

z

w

0.8

I-

z >-

4 I LU

0.6

0.4

> I-

4 -J

0.2

LU

I

-1 .0

-0.8

-0.6

-0.4

-0.2

0

0.2

DISTANCE

0.4

0.6

0.8

1.0

(mm)

2.

U-

I-

Figures

2,

3.

(2) Graph

plots

the

LSFs ofthe new (0.3- and 0.8-mm) and old (1 .0-mm) focal spots.

(3) Graph

plots

new (0.3(1.0-mm)

the MTFs

and 0.8-mm) focal spots.

of the

and

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

2.0

1.8

old SPATIAL

FREQUENCY

(cycles/mm)

3.

2,048

the detectors and sampling aperture, were calculated. Presampling MTFs were measured from images of a slightly angulated slit (6). Signal-to-noise ratios of the old and upgraded video camera were determined. Video signal

current

to the

photoconductive

layer

the 2,048 x 2,048 digital system creased two times, from 400 nA Low-contrast square objects, stacking several squares of film Lucite phantom, were radiognaphed Incident exposures to the surface tom were measured with use of chamber (model 500; Victoreen,

.

A total

of 169

studies

were

at both

matrix

upper

and

obtained sizes

26 lower with

(1,024

the x

jects.

in

was into 800 nA. formed by on a 20-cm at 85 kV. of the phanan ionization Cleveland).

Evaluations

Clinical

GI tract digital

1,024

system and

x 2,048)

Informed

U

RadioGraphics

U

Takahashi

et a!

the

screen-film

was

Twenty-six

of

169

system.

obtained

from

all sub-

upper

GI tract

studies

and six of 26 lower GI tract studies were formed with the upgraded video camera the x-ray tube with the smaller (0.3-mm)

perand focal

spot.

For the upper GI mode of the image used, whereas the ployed for imaging tion

to original

tract studies, the 9-inch intensifier was routinely 12-inch mode was emthe lower GI tract. In addi-

images,

processed

images

were obtained with niques (10, 1 1) that

unsharp masking could selectively

a certain

range

frequency

of an

techenhance

image.

The

form of unsharp masking that we used was expressed as D D0 + K (D0 Dus) where D0 and D were the densities of the unprocessed and processed images, respectively. Dus represented the density of the processed image and was calculated by averaging the densities of the unprocessed image. K was a -

=

weighting

972

and

consent

factor.

In this

study,

Volume

,

the

12

unshanp

Number

5

UI-

SPATIAL

FREQUENCY

(cycles/mm)

4.

U-

Figures

I-

MTFs

4, 5. of the

system play and

(5)

with

system

SPATIAL

FREQUENCY

(cycles/mm)

the

modes for old (1.0-mm) Graph plots

upgraded 5.0

(4) Graph

plots the X 2,048 digital 7- and 9-inch disthe new (0.3-mm) focal spots. the MTFs of the

2,048

2,048 with

x 2,048

the

0.3-mm

digital focal

spot

and 7-, 9-, and 12-inch display modes and of the screen-film system with the 0.8-mm focal

(SF) spot.

5-

masking quency

technique enhanced the spatial frerange at 0.25 line pain per millimeter

(lp/mm)

to two

hard by

copy a laser

The

mask

jectively

times

of each

digital

printer

size

after

and

selected

the

digital

weighting

image the

factor.

was

image

weighting by each

observer performance To compare the with

the

factor observer

screen-film

produced

processing.

experiment. image quality

and

A

were

sub-

before

the

achievable systems,

ra-

diographic exposures of all 195 patients in the same position were obtained within severa! seconds with both matrix sizes of the digital system and the screen-film system. Three senior radiologists subjectively evaluated

the

basis

of overall

digital

images image

and

scored

quality

each

compared

that

of the screen-film images (1 2 slightly inferior, 3 equal, superior, and 5 superior) The averaged for comparison. =

=

=

September

1992

.

=

4

U

RESULTS

.

Basic

Imaging

Properties

Respective LSFs of the new focal spots (0.3 and 0.8 mm) were considerably smaller than that of the old focal spot (1.0 mm) (Fig 2). Respective

MTFs

of the

new

focal

spots

(0.3

and 0.8 mm), especially that ofthe 0.3-mm focal spot, were substantially higher than that of the old focal spot (1 .0 mm) (Fig 3). Overall, MTFs of the new digital system for 7- and 9-inch

display

modes

with

a 0.3-mm

focal

spot

on the

were slightly better than those of the old digital system with a 1.0-mm focal spot (Fig 4) and those of the screen-film system with a 0.8-mm focal spot at lower spatial frequen-

with

cies.

inferior, = slightly scores were

better

However,

MTFs

the

screen-film

at higher

Takahashi

system

frequencies

et a!

showed

(Fig

U

5).

RadioGraphics

U

973

Table 3 Comparison

video

of Signal-to-Noise Size of Image Intensifier (inches)

Matrix

Figure 6. low-contrast tection

Simulated

test.

The

are equivalent, ative

was

dose

used

of the

times

x 2,048

12

66.9

31.6

2,048 2,048

x 2,048 x 2,048

9 7

63.7 79.3

42.3

contrasts

the rel-

system

(b)

of the screen-film

signal-to-noise was increased due

to the

ratio of the new by approximately

reduced

thickness

layer

current

(Table

and

the

b

video two

of the

increase

in the

3).

Detectabi!ities of low-contrast objects with the two systems were similar, even though the incident exposure of the digital system was reduced to one-half of that of the screen-film system

Simulated images of low-contrast square objects were obtained with the 0.8-mm focal spot screen-film system and the 0.3-mm focal spot, 2,048 x 2,048 digital system (Fig 6).

.

(Fig 7).

Clinical

1,024

U

RadioGrapbic.s

U

Takahashi

et a!

Evaluations

GI TraaFamination.-The of images from the 2,048 x 2,048 tem was superior to that of images Upper

x 1,024

and those (P < .01)

974

34.4

(a).

photoconductive signal

Old Video Camera

2,048

a-

The camera

New Video Camera

of

though

digital

New

in the de-

threshold

even

50% of that

system

images

objects

for the Old and

Ratio

Cameras

system

processed (Table

4).

for both

quality

digital from

original

systhe

images

with unsharp masking Processed 1,024 x 1,024

Volume

12

Number

5

5-

E E Cl) Cl)

2

Ui

z

C-)

1’

I-I

0.5

U-

-I

0

0 :

I Cl) Ui

0.2

I

0_i

I-

(2048)

Figure

-I-

2

I

5

10

OBJECT

Table

DIGITAL

#{149} :SCREEN-FILM

50

20

diagram

for the 2,048

threshold

contrasts

for both

X

focal spot and focal spot. The

systems

were

after

Upgrade

the

similar.

4

Comparison

oflmage

Quality

of Digital

System Technique

before

and

Lower

Upgrade

GI Tract

Examination Upgrade After

Before

Upgrade

system 2.37

Processed

3.09

2,048 x 2,048 Original

(n (n

429) 429)

2.81 3.09

(,z

=

=

(n

=

=

411)

2.97

=

41 1)

3.32

(n (n

=

78) 78)

2.42 2.63

(n (n

78) 78)

2.61 2.93

(n (n

= =

(n (n

60) 60)

2.33 2.50

69) 69)

2.72 (n 3. 1 1 (n

=

18)

=

18)

system 2.65

Processed Note-Numbers superior, 5

Systems

GI Tract

Examination Upgrade After

Before

1,024 x 1,024 Original

Screen-Film

and

Upper

3.39 represent =

average

(n (n

scores.

1

=

inferior,

= =

2

=

slightly

inferior,

= =

3

=

equal,

4

=

= =

18) 18)

slightly

superior.

and processed 2,048 x 2,048 digital images were equal or slightly superior to the screenfilm images in image quality. After upgrade of the system, all of the oniginal digital images improved in image quality (P < .01). However, there was no improvement in image quality for any of the processed digital images (Figs 8, 9). Lower original images

GI Tract Fcamination.-For both and processed images, 2,048 x 2,048 were significantly superior in image

quality (Table

4).

2,048

images

September

detail

2,048 digital system with a 0.3-mm screen-film system with a 0.8-mm

( mm)

SIZE

Contrast

7.

to 1,024 x 1,024 images The quality ofprocessed was

1992

almost

equal

(P < .01) 2,048 to that

screen-film and 2,048 1,024

images. x 2,048

x 1,024

Original images

images

were

film images. Although processed 2,048 were equivalent to screen-film

1,024 x 1,024 and processed inferior

to screen-

x 2,048 images

images in im-

age quality before and after the digital system was upgraded, no significant improvement was noted for any original images or for processed 1,024 x 1,024 images after upgrade of the system (P > .05).

X

of

Takahashi

et a!

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RadioGraphics

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975

b

VVV.;r’

I +,

V

#{149}!

f

.A,’’-l

IT

V

d.

C.

Figure

8.

Screen-film

(b),

processed 2,048 (d), and of a 68-year-old

before

(a), original

1,024 x 1,024 (C), original processed 2,048 x 2,048 man with gastric adenoma

upgrade

of the system.

seen

in the

near

posterior

the greater

wall

curvature

A gastric

of the

(arrows

images are inferior to processed ofmatnix, whereas 2,048 x 2,048 with unsharp masking show better cessed 1 ,024 x 1 ,024 images and

quality

1,024

of the screen-film

x 1,024 (e)

2,048 x images obtained

adenoma

is

body

of the stomach in a) . Original images, regardless images processed detail than procome close to the

images.

C.

976

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Takahashieta!

Volume

12

Number

5

One of the crucial limitations of the digital system has been its lower spatial resolution because of the limited number of pixels. However, when a larger matrix size or smaller mode of the image intensifier was used with unsharp masking postprocessing techniques, the image quality and spatial resolution were almost equivalent to those of a screen-film system (1-4). This study has demonstrated that the basic imaging properties and the image quality of the 2,048 x 2,048 digital system are equivalent to those of a screen-film system and that the digital system has great potential for use in various radio!ogic examinations. Improvement in the MTFs of the system and in the image quality of GI tract examinations has been accomplished by upgrading the system, that is, by using a smaller (0.3-mm) focal spot and reducing the thickness of the photoconductive layer of the video camera. One may wonder whether radiography performed with a 0.3-mm focal spot really produces images of better quality, since the exposure time should be increased to allow an adequate dose for the examination of the abdomen, especially the lower abdomen. As has been shown in this study, the exposure dose can be reduced by 50% with the digital system. In addition, our newly developed x-ray tube with 0.3- and 0.8-mm focal spots has al-

!owed

us to use the required

exposure

techniques

are

needed

to

demonstrate

finer structures. Because of the advantages of the digital radiography system with a 2,048 X 2,048 trix,

graphic seems

further evaluation studies of other warranted.

of the parts

system of the

REFERENCES 1.

Feczko PJ, Ackerman LV, Kastan Di, Halpert RD. Digital radiography of the gastrointestinal tract. Gastrointest Radio! 1988; 13:191-

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Steiner E, Mueller rucci JT. Digital

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dose

for radiography of the abdomen without prolonging the exposure time. With use of a smaller (0.3-mm) focal spot, we have found that the signal-to-noise ratio is reduced and that the spatial resolution can be increased. Because fine-network patterns of the colon are so minute, more advanced, high-resolution

U

8.

30, 1990. Takahashi

M, Ueno

S, Tsuchigame

T, et al.

Improvement of physical imaging property a 2,048 x 2,048 matrix image intensifier-television

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radiography

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at the 77th Scientific Assembly and Annual Meeting of the Radiological Society of North America, Chicago, December 1-6, 1991. Takahashi M, Ueno 5, Tsuchigame T, Ito K, Hara M, Kamiya M. A 2,048 X 2,048 matrix image

ma-

digital

of

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digital

radiography

sys-

tem for gastrointestinal examinations. Presented at the 77th Scientific Assembly and Annual Meeting of the Radiological Society North America, Chicago, December 1-6,

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1991. 10.

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Volume

12

Number

5