Computers in Radiology

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MR scanner (General Electric. Medical. Systems. Milwaukee,. WI). The remote teleradiology computer used was a Macintosh. 7100. PowerPC. (Apple Computer,.
Computers WaveletTransform-Based Transmission of MR J. A. Maldjia&,

was

W. C. Liu, 0. Hirschorn,

OBJECTIVE. to develop

teleradiology transfer form

The

an

image-transmission

of MR image

studies

wavelet

for trans-

system

We

for

describe

implementing

an

effi-

teleradiology

capability for transmission of diagnostic MR images. The system uses the wavelet transform to achieve sion, with

greater standard

of less than method using

than 90% image compresmodem transmission times

5 sec per compressed

is inexpensive

The

and can be implemented

commonly

MR scanner

image.

available

and

capabilities.

ily

W. Semanczuk

more

take

compression three

tion

of teleradiology

systems.

of image compression gories: lossless and retain

the fidelity

limited

to two

of the original to three

factors

Although within

ments

by

connected

Transmitting a standard

Received

modem

line (28.8

with

image

Materials System

been

described

Wavelet

with

transform,

fully

operational

functions).

Similar

ever,

unlike

tions

are very

com-

transform

sines

present We cient

of representing

data

this repre-

sines

transform,

cosines,

cosines, in space allows

such

teleradiology

imaging

study

over

transform image compression. can transmit diagnostic-quality

kBps)

would

eas-

in less than

5 sec per

selection,

and

All

basic

compression,

for

was

Supercomputing

Development.

residing

system

data

functions

Applica-

on the remote

designed

IL) and

Champaign,

computer.

specifically

to

work

The with

MR images. eliminating the need for a film digitizer. Figure 1 diagrams the system’s components and overall design. The backbone of the system consists of a SPARC2O workstation (Sun Microsystems, Mountam View, CA) on-site connected via the conventional

1.5-T Signa Horizon MR scanner (General Electric Medical Systems. Milwaukee, WI). The remote

do not

hospital

teleradiology

Ethernet

network

computer

used

(10

was

Mbps)

a

installed

effi-

on wavelet The method MR images

image.

and a 28.8-kBps

modem.

Both

to a

Macintosh

PowerPC (Apple Computer, Cupertino, running System 7.5.3 with Open Transport 7100

typically

highly

these

Software

software

and

data

func-

at characterizing

based

tions

transmission,

at the

has four

How-

the wavelet

as the data

system

and funcwavelet

wavelet

in an image. describe an inexpensive,

21, 1996; accepted after revision January 8, 1997. Department of Radiology (UH-C320), University of Medicine

and cosines

in frequency.

to be very efficient

discontinuous

system

Center

wavelet

This

image

The

(National

and

localized

to infinity.

end).

the remote

the

and

the need for any intervention

(sending

meth-

are more complicated wavelets and mother

localized

to be

(receiving

compression

using

to sines

are

site

decompression and are controlled from site using a standard Telnet connection

to the fast

data

was designed remote

viewing.

transform,

For

the basis functions have been called

site

the

[1-4].

is a method

is performed

host

system from

methods

similar

For a fast Fourier

of image

for lines.

of the original of 20-30: 1 have

these

transform-based

continue

high-speed

features ratios

ods fall into this category. The wavelet transform, data.

Methods

size

components:

functions

methods environ-

and

Design

CA) 1.1

computers

had Interactive Data Language (IDL) version 4.0.1 installed (Research Systems, Boulder, CO). The other software programs used were all shareware including

Fetch

(Dartmouth

College,

Hanover,

NH), Telnet, and Gnuzip (GNU, Free Software Foundation. Cambridge. MA). Gnuzip is a pro-

November

tAll authors: spondence

MR

each

(assuming

The teleradiology

important Compression

but are

institutional

of 30 images

lossless

used

taming image.

image,

lossless contained

if only

were

end) without

tions.

methods

such methods are impractical across conventional phone an entire

in

fall into two broad catelossy. Lossless methods

pression [1, 2]. may be workable direct lines, transmission

These

an hour

Lossy compression methods offer the benefit of higher compression ratios while main-

sentation

mage compression technologies are of paramount importance the development and implementa-

than methods

series

(basis

I

for

Data

Fourier

workstation

Compression

of 137 kB).

compression.

CONCLUSION. cient

system

using

Image

R. Murthy,

of this study inexpensive

purpose

effective,

in Radiology

and Dentistry

of New Jersey-New

Jersey Medical

School, 150 Bergen St., Newark,

NJ 07103. Address

corre-

to J. Maldjian.

AJR 1997:169:23-26

0361-803X/97/1691-23

AJR:169, July 1997

© American

Roentgen

Ray Society

23

Maldjian

et al.

achieved.

For

threshold

is selected

example,

for a 90% such

that

compression,

90%

a

of the wavelet

fall below this cutoff and are set to 0. In sparse storage mode, these zero values are eliminated, resulting in a compact array containing only 90% of the original wavelet-transformed data. coefficients

GINX

MR Scanner Data

Base

(compress

Ethernet

& zip)

This

Fetch modem

PowerMac

concept

accurate

Home

7100

is deceptive

in terms

image

The

file.

pression

is desired,

of elements

& decompress)

by hospital Ethernet lines to scanner

system disk. Remote computer can connectto SPARC2Oworkstation bystandard lnternetTCP/IP connection. MR images are transferred to SPARC2O using GINX. MR images are then waveletand Gzip-compressed. Compressed images are transferred by modem using Fetch to PowerMac, where compression is reversed.

are

cient),

which

Electric

Medical

files

nations

currently

can

be decompressed

across

different

com-

prompts

puter platforms. The

user

to the

a remote

performs

SPARC2O

workstation

percentage logs

into

the MR

IDL

fers

the

appropriate

and invokes gram logs plays the prompted percentage

the teleradiology program. The proonto the scanner system disk and discurrent examinations. The user is for examination number and desired of compression. The appropriate exam-

ncr

is then system

disk

connected,

the user

transferred

directly

to the

SPARC2O.

initiates

from

the

The

compression

for

extracted system

files

disk,

The

transfer

Within

IDL,

the user

(down

to

selected

images.

Thus.

then

uses

Fetch

to transfer

connection

and

the compressed

already allows

some

images

the compression

of the

specifically

lion

Image

starts

the

IDL

compression

(Gzip).

on the Macintosh

the MRUNCOMPRESS widget-driven pression Image [‘he

viewing

PowerPC

program.

graphical and

The

user

user and

This

interface

invokes a

for decom-

of the images.

Selection imaging

network

at our

institution

is con-

nected via a 10-Mbps Ethernet line to an on-site SPARC2O workstation used exclusively for image processing. Images to be compressed must first be transferred to this workstation. This transfer is initiated

remotely

by

a Telnet

connection

to the

SPARC2O. In order to keep user functions to a minimum, all on-site transfer and image compression is handled through a single command, MRCOMPRESS, invoked in IDL. This program invokes an

24

a new

the

program trans-

examination

SPARC2O,

data),

doubles

routine

more

no

is relative

on images

that

and

as

coefficients

integer

arrays

greater

SPRSIN

function

one

20

on the basis of the desired percentage This thresholding is accomplished

retaining

containing

only

the

than returns the

elements

the specified a structure

surviving

wavelet

scale.

and

mode.

10-1000,

This

depending

mapping

is facilitated

is to map This

converts

sparse with

absolute

threshold. of two

the

storage The arrays,

available

or less,

on

within

by storing

the position

integer

=

into

16-bit

images

a unique

of

value

size

must

be

There are 16-bit integer

in the array.

values

in the

-32,767

to +32,767.

indexed

x 256

for

to full

we have

vector

only

position

from

the arrays

modification

because

for every

(256

in restoring

is possible

216 possible

from

65,536).

Array

ele-

0 to the size

of the

the position

val-

Thus,

can be mapped to the integer 16-bit scale by subtracting 32,767 from each position. With these modifications, the 137-kB ues for a 256 x 256 element

image

is now

wavelet

reduced written

A final lossless the

array

to

compression

files are then

coefficients

and the other containing an index to the position of the coefficients in the original transformed matrix. It is within this step that the wavelet compression is

x 256

array

used

The second

are usually

magnitude

of

sparse

ments

mode,

during

in

can

coefficients

which

a nearest-integer

be

on

are

function,

use

these

with

array into row-indexed

during

mapping

is desired

ranging

the IDL SPRSIN

is achieved scale

this

the 16-bit

scale,

using

not

by a factor

filter

transformed

reversing do

this

an integer

been

using

wavelet

to

[5]. Rather,

format.

resulting

data

reduced

used in other wavelet-coding we attempt to maintain one to points of accuracy by multiplying the

has

256

The

data,

into

We

The images are compressed using the built-in wavelet transform function (WTN) within IDL. This function performs a discreet wavelet transform coefficients. thresholded compression.

is only

This com-

Compression

filter

file size

coefficient data

decompression.

storage

wavelet

wavelet-transformed

the largest factor that will maintain

selected.

a Daubechies

an

compression

the size of the original

have

used

images.

16

or CT

the largest 10 coefficients in 32-bit form. thereby decreasing the dynamic range of the data to be mapped. The mapping factor is stored with the

compression)

pertinent

imaging

the 90%

of the

image,

the

compression

schemes

of run-

was

are 32 bit, introducing

times

wavelet

by mapping

rule

has the option

space

image

50-60 kB with 90% compression, achieving actual file compression in the range of 40%. We achieve higher compression ratios by conveiling the 32-bit storage mode of the sparse matrix arrays to 16 bit, removing this factor-of-four increase in size from the original data. For the floating point

and

two coeffi-

of storage

for MR

Thus,

size

is four

in each

wavelet

if the original the case

to the

which

approximately

if more detail

are

However,

and

the amount

in size by two.

three decimal

also

of the

SPRSIN

image.

(position

the new arrays

increase

and series fold-

takes

by

of elements

original

Furthermore,

introduced

then

opens

The

been transferred to the SPARC2O. the user to change the percentage

over the modem connection. Fetch has been configured to automatically reverse the lossless porof

input.

and

and a

1 sec per 256 x 256 image.

scan-

pression

Telnet

to sorting

sion).

the

disk

number

examination

and

ning

closes

to

transferred

the images into the appropriate series and performs a wavelet transform-based compression. The wavelet-compressed data is then compressed further using a lossless technique (Gzip compresuser

the exami-

system

and automatically

scanner

sorted into appropriate

program

sorts

The

(General

on the SPARC2O. The image files are from the image database on the scanner

directory

ers.

displays

scanner

the user for an examination

host

Once

from GINX This

on the

login using Telnet at the

adapted

Systems).

on-site

institution.

ination

C program

compression

will be equal to the number

generated

set. For a 137-kB

external

coefficients,

the number

bit (as is frequently

data,

gram for performing lossless image compression (Gzip) using Lempel-Ziv coding. The compressed

although

wavelet

returned

arrays

in the

arrays required.

is networked

compression,

of actual

arrays

of the resulting

shows that SPARC2O workstation

90%

floating point (32 bit) for wavelet coefficients and long integer (32 bit) for matrix position. If no corn-

(unzip

Fig. 1.-Diagram

of

in terms of surviving

18-25

is applied.

kB

to the appropriate

image compression

wavelet-compressed

files

using

program

Gzip, which uses Lempel-Ziv

achieves

another

twofold

when

These

to threefold

90%

compressed directories.

is appliedlo the

shareware

coding. decrease

This in the

AJR:169, July 1997

Image size of the files, reducing range

(94%

of information

for

Transmission

of MR Data

them to the 9- to 12-kB

compressed

files).

This

compression

performed on the SPARC2O workstation. ing can be reversed on different platforms loss

Compression

using

is

The codwithout

the appropriate

shareware

program for that platform (i.e., MacGzip for the Macintosh). The process of wavelet compression. conversion to sparse mode. and lossless Gzip compression takes approximately 4 sec per 256 x 256 image

on the SPARC2O

Image

Transmission

The

wavelet-compressed

transmitted

Fetch.

This

to automatically

rates

via

Internet

is easily

Theoretically,

files

as they

high

and

rates

vented

by establishing

modem through

can

modest

volumes

the transmission

to the SPARC2O

a 28.8-kBps range

speeds,

transmitted

reduce

Image

be configured

connection

At the more

file

can Gzipped

using

a TCP/IP

are 2-3 kBps,

as 6 kBps.

are

the shareware

program the

files

using

using MacGzip (GNU, Software Foundation. Champaign, IL). Typi-

transmission

connected

site

unzip

are transferred Development

pressed

Gzipped

to the remote

program

cal

workstation.

the

as high

each

com-

in less than

5 sec.

of Internet

traffic

Fig. 2-67-year-old no compression, 94% compression,

man with hemorrhagic infarct of right basal ganglia. T2-weighted MR images displayed with 90% compression, and 94% compression show that details of image are retained at 90% and including hemorrhage with hemosiderin ring (arrowon 90% compressed image).

can

rate. This can be circuma direct

modem

connection

workstation.

Decompression

All image decompression and viewing is performed in IDL on the Macintosh PowerPC. A program was written with a graphical user interface for performing these functions. The decompression process

simply

restores

the

sparse

storage

form

of

the compressed images to full storage mode. remapping the wavelet coefficients to floating point (truncated at .01-.000l) and the matrix position vector to the appropriate matrix elements. The inverse

wavelet

transform

array to obtain ing

program

and

is then

the decompressed incorporates

magnification

simple

controls

images.

Reconstruction

image

on the Macintosh

applied image.

time

view-

window,

for

level,

displaying

for a single

7100

to this The

256

is less than

the x 256

4 sec.

Results The image

quality

the compression Figure

that can be achieved

scheme

2. These

outlined

images

with

is shown

are displayed

in

at origi-

nal resolution and at 90% and 94% compression. The original image file size was 137 kB. After wavelet and Gzip compression, file sizes were

reduced

The

90%

to 15 kB and 8 kB, respectively. compressed

image

loss of image

detail.

image

the key diagnostic

retains

original

image.

Even

Some

shows

the 94%

image

minimal

compressed

features blurring

of the

however,

particularly

at sulcal

boundaries

and

at gray

matter-white

matter

interfaces.

This

can be noted

AJR:169, July 1997

in cortex. (arrow) with 90% and 94% compression.

is evi-

dent,

in Figure

Fig. 3.-62-year-old man with small infarct in left motor cortex. A, T2-weighted MR images show subtle area of high signal intensity B, Balanced MR images also show subtly increased signal intensity

2, with progressive

decrease tion

in sulcal

of the internal

tralateral

to the

defmition

and loss of resolu-

and external area

capsules

of hemorrhage.

conDespite

this blurring,

subtle

at 94%

compression

pressed

image

can

detail (Fig.

can be retained 3). The

be transferred

90% over

even coma con-

25

Maldjian

ventional

modem

decompression compressed formed

line

within

see,

5

with

eral

in less than 4 sec. For the 94% image,

within

both

processes

Electric

easily

can be per-

More image

We

describe

an

networking

gram,

IDL, license.

data.

The

infrastructure

costs remote

7100,

obtained

for less than

software

used

about

is widely

imaging

require

are not capable data.

windows,

soft-tissue

within

the

dural

windows.

These

for

a

a Macinpow-

networking and can

be

via the Internet at no cost. The component of the system is the

the

transfer

as a separate

($20,000-$30,000), a similar

most workstation

to the MR scanner.

tions usually perform volume reconstructions Windows

These

pur-

university

diagnostic

the

associated

lower

substantially transfer

larger

Workstation;

times.

commercial

size

methods

(one

of

the would for use

images. involve require We

More more

easily

is

resulting for

these

is being

Tl -weighted,

complicated than

200

axial more cases

images,

which

120 easily would

transmission times of more than 1 hr. describe a teleradiology system that

can effectively compress, compress a 256 x 256 MR

and

approximate

original

raw

need

for

desired

data.

separate

images.

flexibility

trans-

The

system

to allow

compression

the user

ratio.

Fur-

the remote

login,

specific

key images

to compress

ratio

if better

method

can

resolution

be easily

institutions

components

the user at

is needed.

implemented

that already

have

at

the essen-

in place.

transfer, and image within

References 1. Aberle DR. Gleeson F, Sayre JW, et al. The effect of irreversible image compression on diagnostic accuracy in thoracic imaging. invest Radio! 1993:28:

398-403 2. Goldberg

MA,

Pivovarov

de10-

M. Mayo-Smith

WW,

et al. Application of wavelet compression tized radiographs. AiR 1994:163:463-468 3. Angelidis PA. MR image compression

wavelet transform

enhanced than can

This

quality

through

tial networking

are on the order of 30 this may be barely

T2-weighted, with

a lower

the

images

for

ratios

(sagittal

the

can select

many

adequate for a CT examination of 30 images, this would be unacceptable for an MR study sequences

to enter

with

with

resulting

of the

windowed

thermore,

sub-

which

the

was designed

and

times

of

compression The

range

eliminates

mission

images

and

Transmission

used by our department) sec per image. Although

already

Gem-

this

compression file

This

grab-

frequently

stage,

the dynamic

remote

the penalty

worksta-

CPU-intensive image and manipulations

methods

at the compression

dual-echo

26

maintain

of

window,

90-94%

transpar-

frame

separate

using

transform.

of transmitting

of

15 sec wavelet

faster

axial

investment

Advantage

be

compression. may perform

Tl-weighted)

(e.g.,

can

On most

some form of lossless image Although lossless methods

a substantial have

run

For a CF scan,

bone

computer,

available

which

raw

three

networked

can

methods

the

$1500

The

bers,

with

hospitals

but

rely on image

sys-

is not a particularly

$2000.

conventional transmission

SPARC2O workstation networked to the hospital MR scanner. Although this can represent chase

process

The

or expensive platform. More powerful, generation PowerPC computers can be

downloaded essential

this

using

setting. It requires the use available software pro-

which

tosh PowerPC

capa-

cost-effective,

university hospital of a commercially

erful later

of MR

is extremely

existing

easy-to-use

teleradiology

for transmission

tern

user

efficient,

for implementing

bility

Systems),

to run IDL as well.

ently in the background via remote login without affecting the normal daily activity.

Discussion

method

Medical

configured

workstations,

8 sec.

et al.

Imaging 4. Goldberg Making

coding algorithm.

sion

using

Magn

a

Reson

1994:12:1111-1120 MA, global

Sharif

HS,

telemedicine

Rosenthal

DI,

practical

architecture

in a PACS

for medical

environment.

Med

et al.

and afford-

able:demonstrations from the Middle 1994:163:1495-1500 5. Azpiroz Leehan J. Lerallut iF, Magana processor

to digi-

image

East. AiR I. A multicompres-

Prog

Technol

1994:20:101-110

AJR:169, July 1997