Reproduction of medical image on web-like reproducing material

In reproducing medical images which are supplied in digital form and which vary in size, a web-like reproducing material is used. The reproducing material is cut at variable lengths in correspondence with the sizes of the images.

The application claims the benefit of the U.S. Provisional Application No. 
60/008,590, filed Oct. 9, 1995 
1. FIELD OF THE INVENTION 
The present invention is in the field of digital radiography. The invention 
relates in particular to hard copy recording of medical images provided in 
the form of a digital image representation. 
2. DESCRIPTION OF THE STATE OF THE ART 
In the field of digital radiography a wide variety of image acquisition 
techniques have been developed that render a digital representation of a 
medical image. 
Among such techniques are computerised tomography, nuclear magnetic 
resonance, ultrasound detection, detection of a radiation image by means 
of an image intensifier, CCD sensor or a video camera, radiographic film 
scanning etc. 
In another technique a medical image, for example an X-ray image of an 
object, is stored in a screen comprising a photostimulable phosphor such 
as one of the phosphors described in European patent application 503 702 
published on 16.09.92. 
In a read out station the stored radiation image is read by line-wise 
scanning the screen with stimulating radiation such as laser light of the 
appropriate wavelength, detecting the light emitted upon stimulation and 
converting the emitted light into a digital signal representation that can 
be subjected to different kinds of image processing techniques. 
After read-out the residual image left on the photostimulable phosphor 
screen is erased so that the screen is again available for exposure. 
The original digital signal representation of the image acquired by one of 
the above acquisition techniques or the processed digital signal 
representation of the image can then be applied to a hard copy recorder 
for reproduction of the image on a hard copy material such as photographic 
film. 
Conventionally hard copy recorders record a hard copy image on recording 
material provided in sheet format. 
For example, the photographic film recorders available on the market 
nowadays, are equipped with a number of dispenser magazines comprising 
different sheet formats. Typically these printers feature two film formats 
on-line. 
For example Agfa's MATRIX LR 3300 is a laser recorder that can handle 4 
different film sizes: 20.3 cm.times.25.4 cm (8 inch.times.10 inch), 27.9 
cm.times.36.5 cm (11 inch.times.14 inch), 36.5 cm.times.36.5 cm (14 
inch.times.14 inch) and 35.6 cm.times.43.2 cm (14 inch.times.17 inch). 
This laser recorder allows the simultaneous availability of two film 
formats during operation. 
The size of the recording material can then be selected from the sheet 
formats made available by the recorder. The image formats and image lay 
out used in such recorders are freely programmable. They can be adapted to 
the operator's choice. 
Depending on the original (digital) image size (pixel matrix) selected film 
size and image format as well as the memory capacity in the recording 
unit, the images are rescaled to fit in the selected format. 
Most conveniently, the radiologist's regarding image lay-out are 
pre-programmed and stored. 
From the viewpoint of optimal use of the film area, for each aspect ratio 
of the medical images, a film format should be available that has the same 
aspect ratio. 
However, as described hereinabove, the number of film formats is limited so 
that in some cases the film will not be optimally occupied by the recorded 
image. Consequentially there is a waste of unused recording material. 
For example, when an image that has been stored in a 18 cm.times.43 cm 
format photostimulable phosphor conveying cassette, is to be reproduced by 
means of a hard copy recorder provided with two on-line film formats, for 
example 20.3 cm.times.25.4 cm (8 inch.times.10 inch) and 35.6 
cm.times.43.2 cm (14 inch.times.17 inch), there is no film format with the 
same aspect ratio as that of the image and hence a best choice must be 
made between the available film formats. Consequentially the film will not 
be optimally filled. 
3. OBJECTS OF THE INVENTION 
It is an object of the present invention to provide a system for 
reproducing a medical image provided by a digital signal representation 
wherein the consumption of recording material is decreased. 
It is a further object of the present invention to provide such a system 
wherein the recording material is optimally filled with image information 
in cases where medical images of a wide variety of formats are reproduced. 
Still further objects will become apparent from the description 
hereinbelow. 
4. STATEMENT OF THE INVENTION 
The above objects are achieved by a method of reproducing on a reproducing 
material medical images of various sizes, that are provided in the form of 
a digital signal representation, characterised in that 
(i) said medical images are reproduced on a reproducing material that is 
provided in the form of a web; and 
(ii) said web is cut at variable lengths that correspond with the sizes of 
the reproduced images. 
Another aspect of this invention relates to a system for reproducing on a 
reproducing material medical images of various sizes, provided in the form 
of a digital signal representation, characterised in that 
means are provided to accommodate said reproducing material in the form of 
a web, and 
means are provided for cutting said reproducing material at variable 
lengths that corresponds with the sizes of the reproduced images. 
The present invention is applicable to the reproduction of all kinds of 
medical images acquired by various kinds of image acquisition apparatus. 
The system is however especially designed for application in the field of 
digital radiography based on photostimulable phosphor technology such as 
that which has been described hereinabove. 
In such a system a great variety of formats of photostimulable phosphor 
screens are used. The selected format depends on the type of examination 
that is performed. 
After read out, images of different formats are sent to a recorder that, as 
described hereinabove, commonly features only two or three different 
formats of recording material. So, non-optimal filling of the reproducing 
material is frequently encountered when conventional hard-copy recorders 
are used in this specific field of application. 
The specific procedure followed in a system wherein radiographic images are 
recorded on photostimulable phosphor screens is described hereinbelow with 
reference to the drawings. 
Basically, the length of the web-like recording material that will be cut 
is determined for each format of cassette conveying a photostimulable 
phosphor screen. This length is stored in advance in a data base or in a 
look up table. It is retrieved at the moment of read out of the image. 
The data regarding the length of the recording material then accompany the 
read out image data to the recorder. There they are interpreted by the 
recorder and used to control the operation of cutting means. 
Alternatively the data regarding the length of recording material to be cut 
is stored for each cassette type in the recorder itself and data 
concerning the cassette type accompany the read out image data sent to the 
recorder. 
The inventors ran an experiment wherein different radiologists had to 
evaluate a number of reproduction formats for different types of 
examinations. They were asked to indicate the minimal acceptable 
dimensions of each image. 
It was concluded that the width of the images had to be situated within the 
range of 17 cm to 30 cm. 
An optimal width of the reproducing material was found to be 22.9 cm (9 
inch). 
However, a photographic material having a width of 22.9 cm (9 inch) is not 
among commercially available photographic materials at the present time. 
The closest width commercially available being 25.4 cm (10 inch) is thus 
selected.

6. DETAILED DESCRIPTION OF THE DRAWINGS 
The present invention will be explained hereinbelow with reference to the 
reproduction of a radiographic image that has been stored in an 
intermediate storage medium, more specifically in a photostimulable 
phosphor screen. 
A system wherein the method of the present invention can be applied 
basically comprises an apparatus (1) for acquiring a digital signal 
representation of an image, in this described case through the 
intermediary of a photostimulable phosphor screen; and a reproducing 
station (10) for reproducing the medical image. 
An identification station (4) is provided for identifying an image and, 
since in most applications the digital signal representation of the 
medical image is subjected to signal processing, a signal processing 
station (7) is also shown. 
An X-ray image of a patient was recorded on a photostimulable phosphor 
screen by exposing said screen to X-rays emitted by an X-ray source (2) 
and transmitted through the patient (not shown). 
The stimulable phosphor screen was conveyed in a cassette (3) provided with 
an electrically erasable programmable read only memory (EEPROM) (5). 
After exposure the cassette/screen combination was identified in an 
identification station (4). Here, patient demographics and examination 
type data were written onto the memory chip (5) provided on the cassette 
(3). Patient demographics are the patient's name, date of birth, sex etc. 
The examination type data are particularities on the performed type of 
examination. 
The EEPROM further stores a number of invariable data among which is the 
cassette format. 
Next, the cassette (3) was fed into a radiation image readout apparatus (1) 
where the information stored in the EEPROM and the image stored in the 
photostimulable phosphor screen were read-out. 
The read out apparatus comprises storage means that are loaded in advance 
with a look up table comprising for each possible type of examination and 
related cassette format, parameters relating to the reading process such 
as adjustment parameters for the detector for detecting the image, 
parameters to be used during image processing, as well as parameters that 
relate to the hard copy output and archival functions. The parameters have 
been selected in advance, and are tailored to the needs and preferences of 
the radiologists. 
The read-out procedure itself is illustrated in FIG. 2. The cassette 
conveying the screen was opened and the screen was taken out of the 
cassette and conveyed to a read out section. 
The stored image was read-out by scanning the phosphor screen with 
stimulating rays emitted by a laser (14). The stimulating rays were 
deflected into the main scanning direction by galvanometric deflection 
means (15). The sub-scanning was performed by transporting the phosphor 
screen in the sub-scanning direction indicated by arrow (16). The 
stimulated emission was directed by means of a light collector (17) onto a 
photomultiplier (18) for conversion into an electrical signal 
representation. 
The sensitivity of the photomultiplier was adjusted in accordance with the 
adjustment parameters that were stored in advance in the above look up 
table. The correct adjustment parameters were identified on the basis of 
the identification data of the image that was read out of the EEPROM on 
the cassette. 
Next, the signal was amplified by square root amplifier (19), sampled by a 
sample and hold circuit (20), and converted into a 12 bit signal by means 
of an analog to digital convertor (21). 
The digital raw image signal (22) was sent to the image processing module 
of the read-out apparatus (FIG. 1, numeral 7) where it was stored in an 
internal buffer. 
The read-out signal was also applied to a preview monitor (8) for display 
immediately after read-out, thereby providing the operator with an early 
feed back in case anything went wrong. 
In processing unit (7), image processing parameters were selected from the 
look-up table described hereinabove in accordance with the information 
read out of the EEPROM. 
The digital image signal was subjected to a decomposition into detail 
images at multiple resolution levels and a residual image. These detail 
images and residual image were then transmitted from the image processor 
to an image workstation (not shown) via a digital communication channel 
where they were stored on hard disk. 
On-line processing generally comprises a modification of the detail images 
which may serve various purposes followed by a reconstruction of a 
processed image by applying an inverse transform to the modified detail 
images and the residual image, the reconstruction process being such that 
when it would have been applied to the unmodified detail images and the 
residual image this would have resulted in the original unprocessed image 
or a close approximation thereof. 
The read-out apparatus (1) including processing module (7) were further 
connected to a workstation (11) and associated review console (12) where 
off-line processing was performed. For the purpose of setting image 
processing parameters for the off-line processing and for determining the 
reproduction format, the data read from the EEPROM are transmitted 
together with the image to the workstation. 
The look up table comprising processing parameters and data regarding the 
reproduction was also stored in advance in the workstation. 
The image processing parameters and the data regarding the output format 
corresponding to the data read out from the EEPROM were retrieved from the 
look up table and applied for image processing and reproduction. 
The read-out apparatus as well as the workstation were connected via a 
buffer (9) to an reproducing device (10). 
FIG. 3 schematically shows a printer that is suitable for use in the 
context of the present invention. 
The device comprises a supply cassette containing a roll (34) of 
reproducing material in web form. In this embodiment the reproducing 
material is photographic film. It further comprises cutting means (30) and 
means (37) for activating said cutting means in response of two control 
signals (31) and (32). Signal (31) indicates the length to be cut from the 
reproducing material and signal (32) is indicative of the length that is 
unwound from the supply roller (34). The reproducing device further 
comprises a recording section (33), that is of the internal drum type in 
the illustrated embodiment, and a processing section (35) where the 
photographic film material is developed. The operation of this recording 
device is as follows. Film is unwound from supply roller (34) and fed past 
un-activated cutting means (30). The cutting means are in a retracted 
position so that they do not have contact with the film. Cutting means 
(30) are activated by control means (37) once a length of reproducing 
material has been unwound that corresponds with the length represented by 
control signal (31), the length being measured by a measuring means (not 
shown) that generate a control signal (32) indicative of the unwound 
length. 
Measuring means for measuring the length of recording material are 
sufficiently known in the art, for example a photodiode can be used to 
produce a signal during the period of time the reproducing material is 
transported past the diode. Knowing the velocity of the movement of the 
recording material past the diode, one can deduce from the known velocity 
and the measured time period the length that has been unwound and the 
cutting means can be activated once the unwound length corresponds with 
the predefined length to be cut. 
Then, the film is transported to a recording section (33) where it is held 
in tight engagement with the inner surface of a drum, e.g. by means of 
clamps or vacuum attraction. 
The film is scanned with a laser beam which is modulated in accordance with 
the signal representation of the image that is to be recorded. 
Upon termination of the recording, the film is transported to a processing 
section (35) to be developed. The reproduced image then leaves the 
apparatus at output (36). 
The described embodiment is a laser imager of the internal drum type that 
includes a developing station. 
It will be clear that the type of reproducing device is irrelevant in the 
context of the present invention and that other types such as thermal 
printers, electrophotographic printers etc. as well as reproducing devices 
that do not incorporate a processing section fall within the scope of the 
present invention.