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PERFORMANCE CHARACTERISTICS OF A LASER SCANNER AND LASER PRINTER SYSTEM FOR RADIOLOGICAL IMAGING SHIH-CHUNG B. Lo,’ RICKY K. TAIRA,’ NICHOLAS J. MANKOVICH,’ H. K. HUANG’* and HIROSHI TAKEUCHI’ ‘Division of Medical Imaging, Department of Radiological Sciences, University of California, Los Angeles, CA 90024, U.S.A. and 2Konishiroku Photo Ind. Co. Ltd, Tokyo, Japan (Received
11 March 1986; received,for publication 4 July 1986)
Abstract-This paper describes the performance characteristics of a laser scanner and laser printer system for radiological imaging. The laser scanner can digitize a 14” x 17”X-ray film to 2000 x 2400 x 10 bit in about 100 s. The laser printer can format 16 images on a 8” x 10”or 14”x 17”film with up to 2300 x 3050 x 8 bit resolution in about 50s. Our experiments show that the laser scanner and the laser printer have a spatial resolution of 3 cycles/mm with excellent spatial linearity and flat field response. This system is a major component of a picture archiving and communication system in a digital-based radiology department. As a stand-alone system, it has certain clinical applications such as a contrast enhancement of radiographs and potential dose reduction to the patient. Digital imaging
An estimated 80% of todays medical imaging procedures employ traditional screen-film technology [l]. In order to realize a computer-based picture archiving and communication system (PACS) for diagnostic radiology, methods must be developed to convert X-ray film images into digital data. The potential advantages of a PACS system include better image data management and protection, rapid access to distributed image databases from different diagnostic modalities, and the availability of an inexhaustable number of copies of each image [2,3]. Current digitization methods include the video camera, the optical drum scanner, the solid-state camera, and the laser scanner. The use of the video camera to digitize film is acceptable only for screening purposes because its spatial and density resolution are insufficient for use in detailed diagnosis. The drum scanner has high spatial and density resolutions but its digitization speed is low and the film aligment procedure is tedious. The solid-state camera, which has the potential to be an excellent X-ray film digitizer, requires further development to increase its spatial and density resolutions. The laser scanner combines very high spatial and density resolution with a reasonable scanning time, it is the best X-ray film scanning technology available today. Film will continue to play an important role in the radiology department even as PACS becomes a reality. Therefore, it remains necessary to evaluate the methods which reproduce digital images on film with high image fidelity. The current method of putting digital images onto film is through video technology. Video cameras have relatively low density and spatial resolution as compared with the laser printer. They also suffer from spatial nonlinearity at the periphery of the image field (as will be later demonstrated) as well as from field density nonuniformity. These distortions will become clinically significant when it is required to reproduce a digitized conventional radiography which contained abnormalities in the periphery of the original X-ray film. The laser printer, although expensive, has proven to be an excellent device in reproducing digital information in the printing industry. The expected cost of the laser scanner and laser printer is about $40,000 and $60,000 respectively. * Please address correspondence Los Angeles, CA 90024, U.S.A.
to: H. K. Huang, DSc., Department of Radiological Sciences, University of California, 227
SHIH-CHUNGB. Lo et d
Laser scanning devices utilize a narrow, intense beam of light that is easily deflected. Many of the limitations inherent in video electron beam scanning (poor MTF, veiling glare, phosphor grain noise, inadequate optical power)  are overcome with laser technology. The high energy incident per unit area of the scanning spot enables these devices to employ low numerical aperture beams which have a large depth of field. They read or write data with a rectilinear raster scaning motion with rapid retrace. Unlike video scanning, the laser light is deflected over a single line of the image instead of over the entire field. The scanned media (film) is then moved to the next line by a mechanical transport system. As in video, the image to be read (or written) is continuously represented in the scanning direction and discretely sampled (written) perpendicular to the beam sweep [5,6]. It is anticipated that laser scanning and laser printing systems will be increasingly commonplace in future radiology departments. This paper describes the first such prototype laser scanner and laser printer system which is available for clinical evaluation. The emphasis of the paper is on the methodology of evaluating such a system and some of its clinical implications. MATERIALS The prototype laser scanner and printer, developed by the Konishiroku Photo Ind. Co., Ltd, were interfaced to a VAX- 11/750 by Digital Equipment Corporation in the Image Processing Laboratory via two separate DR-11W direct memory access (DMA) parallel interface boards. The computer coordinates DMA input/output (I/O) functions, chooses laser scanner and printer operating parameters, synchronizes data acquisition and mechanical movements, and monitors the operating status of the machines. Our laboratory has developed a software package that allows for easy and reliable daily clinical operation of the scanner and printer. More than 500 X-ray films have been digitized and 300 digital images have been written onto film with this system. Laser scanner description
The laser scanner digitizes a 14 x 17 in. X-ray film at a resolution of 2000 x 2400 x 10 bit. It scans at a speed of 229 lines/s. A variety of film sizes can be scanned and several optical density range setting can be selected to capture a full 10 bits of information. Radiographs may be read either as positives or negatives and the region of interest to be scanned on the film is controlled by software. The laser scanner has a full width at half maximum spot size of 110 pm in the scanning direction and 130 pm perpendicular to the scan direction. The sampling distance in both directions is 175 pm. Figure I(a) shows a block diagram of the laser scanner system. The scan process can be described as a repetition of the following sequential steps: (a) a 5 mW helium-neon (He-Ne) laser (Uniphase 1105P, U.S.A.) and a rotating 8 facet polygonal mirror system (Copal Electronics PD60D, Japan) is used to quickly scan across a 175 pm wide line of the inserted radiograph; (b) the light transmission of the laser through the radiograph is measured and converted to optical density data using an optical fiber coupling bundle, a photomultiplier tube (Hamamatso, Photonics R550, Japan) and a negative logarithmic amplifier ; (c) the optical density for each 175 x 175 pm2 area along the scan line is quantized to ten bits by an analog to digital converter; (d) a data controller unit sends the optical density scan line data to the computer through a parallel DMA interface; (e) a mechanical transport system moves the film to the next scan line. Synchronization of the film transport and the transmission of line data to the computer is accomplished by closely coupled communication between the DMA interface, the host computer, and the microprocessor located within the scanner. Laser printer description
The laser printer writes a digital image onto 8 x 10 or 14 x 17 in. red sensitive film with a film advance speed of 16 mm/s. An 8 x 10 in. film can be written at up to 2384 x 3050 x 8 bits resolution. Each pixel corresponds to an 80 x 80 s pm2 area. Image magnification and minification are available and a maximum of 16 images can be formatted onto either size film. Figure l(b) shows a block diagram of the laser printer system. Digital image data supplied by the VAX-11/750 host computer is sent to a five megabyte printer image formatter module through a dedicated DMA interface board. This data is sent through a programmable look-up table (LUT) in
Laser scanner and printer for imaging
V-4 Fig. 1. (a) Block diagram of. the laser scanner. (b) Block diagram of the laser printer.
the printer which corrects for nonlinearities in the laser production of film density. This look-up table is calibrated with the optical density to gray level transfer characteristics of the scanner. The output signal from the look-up table is then used to modulate the intensity of a 5 mW He-Ne laser beam (Uniphase 1105p, U.S.A.) using a lead molybdate (PbMo,) acousto-optic modulator (NEC OD88lOA, Japan) such that the input data will be linearly mapped into optical density on film. A conventional X-ray film processor (Kodak RP X-OMAT film processor with 90 s processing time with operating temperature 34C) is used. However, the red sensitive film requires a green safe light in the darkroom. The performance of the laser printer was verified by using two different densitometers, a Sakura PDM-5 scanning microdensitometer with a resolution of 10.0 pm and a Macbeth TD502LD densitometer with an aperture size of I .Omm. METHODS Laser scanner
The mapping of optical density to gray level for the laser scanner was measured by scanning a calibrated Kodak single emulsion photographic step wedge, Kodak catalog number 152 3406
SHIH-CHUNGB. Lo et rd.
calibration number 310-ST-252 (composed of silver halide particles suspended in a gelatin) and recording the optical density of the each step and the resulting digital output value. The quoted accuracy of the step tablet is kO.02 optical density. The tablet consists of 21 optical density steps which range from optical density 0.063.09. A 2000 pixel average for the digital output value was computed for each step. Precise measurement of the accuracy of digitization is difficult due to the inavailability of constant optical density film that is perfectly uniform and free of noise. It is impossible to distinguish whether the source of the nonuniformity or noise is due to the scanner or inherent on the film. Field uniformity was measured by scanning the calibrated step wedge at five different locations along the scan direction. The measurements of nonuniformity (overall constancy) and noise (local constancy) were performed on 10 x 10 pixel area blocks (1.75 x 1.75 mm) of the Kodak step wedge. These locations corresponded to various degrees of offset from the center of the scanning field. The scanning line covered a distance of 14 in. The 500 data points from each step (100 points from each location) were then used to calculate the root mean square (r.m.s.) fluctuation from a constant input to the system. We assumed that the 10 x 10 area was large enought for statistical accuarcy and small enough to avoid any nonuniformities present on the step wedge. The laser scanner’s frequency response was tested by scanning a high precision microlithographed United States Air Force (USAF) 1951 line pair pattern which consists of alternate and equally spaced dark and light stripes at different spatial frequencies oriented both parallel and perpendicular to the scanning beam direction. The dark and light areas correspond to optical densities 0.05 and 3.40 respectively. The average gray level for the dark and light stripes were extracted from the digitized image and the contrast frequency response (CFR) calculated for each frequency. The CRF parallel to the scan direction was determined from line pair patterns oriented perpendicular to the beam traversal direction and the perpendicular CRF from line pair patterns oriented parallel to the scanning laser beam. These values indicate the degree to which contrast depends on spatial frequency and is given by . CFR~)
= otn~~cf) -
where D,,..cf) D,Jf)
= Digital value of dark stripe = Digital value of light stripe
f = Spatial frequency of the stripes.
The gray level to optical density transfer characteristics for the printer were investigated by writing a computer generated gray level step wedge with 256 levels and measuring the corresponding optical densities using the Macbeth densitometer. Analyses were performed over the entire writing field (flat field response) as well as over local regions of interest (noise). We used two methods to determine the resolution of the laser printer. In the first method, the modulation transfer function (MTF) parallel to the scan direction (Fig. 8) was determined by obtaining the optical density profile distribution through the center of the imaging spot in the direction parallel to the scanning beam. The profile data was then corrected for the nonlinear transfer characteristics of the film by knowledge of the H-D characteristics of the film used. The MTF was obtained by computing the modulus of its Fourier transform. As a second method of assessing the spatial resolution, the contrast frequency response was determined by printing a computer generated line pair image on film and measuring the densities across the line pair pattern on the printed film using the high resolution scanning microdensitometer. The spaces and lines corresponded to optical densities of 0.16 and 2.3 respectively. The spatial linearity parallel to the scan direction of the laser printer was investigated by printing out an ideal computer generated image consisting of parallel and equal spaced lines (see Fig. IO) and observing the deviation of the lines on the resultant film from the ideal both in nonlinearity and in angular orientation. This was accomplished by performing a digital subtraction of the resulting film with a 180” rotation about the normal axis of the same film. The resultant subtracted image provides visualization of vertical distortions of the lines parallel to the scan direction. Similarly, a subtraction
Laser 1024 896
for imaging /
Fig. 2. Relationship
gray level value for the laser scanner.
of a film with vertical lines from a 180” rotation about the axis parallel to the scan direction of the same film results in visualization of distortions parallel to the scan direction. The subtractions were performed using a vidicon camera connected to a Gould IP8500 image processor which digitizes to 5 12 x 5 12 x 8 bits. The effects of the distortion correction mapping of the vidicon camera used in this experiment were tested by digitizing a test image known to be highly linear and performing the above subtractions. The subtraction of the image from its 180” rotated image was seen to produce a highly uniform result thus validating the technique as a good indicator of image linearity. Clinical applications
The laser scanner and printer system has the potential of reducing the dose needed for a given X-ray procedure while still being able to produce a clinically acceptable radiograph. Figure 1l(a) shows radiographs of a rabbit taken with successively reduced amounts of X-ray exposure. These radiographs, taken using conventional screen-film techniques (DuPont Cronex 4 Film and Dupon Cronex Hi Plus Screen) were digitized using the laser scanner and the resultant digital image routed through the look-up table of the laser printer. The printer was loaded with a linear look-up table using window and level values obtained by measuring the maximum and minimum optical density seen on the film. RESULTS
Figure 2 is the optical density to gray level transfer curve for the scanner and shows that the digitization of optical density is highly linear over the entire step wedge range (from optical density 0.06 to 3.09). Linearity in this range (from optical density 0.06 to 3.09) covers essentially all films
Fig. 3. Flat field response. Plot showing the change in the standard deviation of optical density over the density range of both the laser scanner and printer. Data were accumulated over the entire imaging field (global variations).
SHIH-CHUNGB. Lo el 01.
0.006 t 0.005 0.004 0.003 1 A
Fig. 4. Noise values. Plot showing the change in the standard deviation of opitcal density over the density range of both the laser scanner and printer. Data were accumulated over small regions of interest (local variations).
produced in todays radiology departments. Figure 3 summarizes the overall conversion repeatability of the scanner determined by computing the r.m.s. fluctuation from 500 digitized points for each step. Field nonuniformities parallel to the scan direction arise mainly from fluctuations in the laser output intensity , nonuniformities in the fiber optic light coupling, and quantum noise in the light detection system. Nonuniformities perpendicular to the scan direction arise from longer term drift of the laser intensity and from lower frequency noise and drift in the detection electronics. The overall flat field response of the system is the combined responses in the parallel and perpendicular directions. Noise values were determined by scanning 10 x 10 square pixel area blocks and calculating the standard deviation of the resultant gray level values. The standard deviation from the five different locations along the scan direction were averaged and the results shown in Fig. 4. Figure 5 shows the contrast frequency response curves for the laser scanner in directions parallel and perpendicular to the scan direction. The response drops to 0.5 at a frequency of 2.9 c/mm in the direction parallel to scan direction and 3.5 c/mm in the direction perpendicular to the scan. As noted by Geiger and Doi [lo], it would appear (due to the relative sizes of the sampling distance and the sampling aperture) that aliasing artifacts would be produced by this system when digitizing a radiograph that contained substantial high frequency content (e.g. bone fractures, mammograms, X-ray images obtained with grids). However, in the direction parallel to the scanning direction the frequency response also depends upon the temporal response of the light detection system and associated electronics. Aliasing artifacts that would originate because of the sampling parameters (sampling distance, spot size, and spot shape) are filtered by the limited bandwidth of the detection system. Thus aliases were not observed when scanning images with substantial high frequencies in the direction parallel to the scan line. In the direction perpendicular to the scan however, the response characteristics of the detector system are not important because of the relatively long time delay between sampling adjacent pixels in the perpendicular direction as compared to the parallel direction.
Fig. 5. Plot showing
TO THE SCAN
spatial frequency the laser scanner.
TO THE SCAN
Laser scanner and printer for imaging 4.0 3.6
Fig. 6. Relationship between the input digital gray level and output film optical density for the laser printer.
Thus when scanning radiographs with perpendicular frequency components greater than the Nyquist frequency of the scanner (2.8 c/mm) aliasing artifacts are observed. Note that although the spot size parallel to the scan direction is smaller than in the perpendicular direction, its high frequency response is lower. This is because the scanning system tested in this paper was limited in response by the detector system bandwidth which behaves as a low pass filter. This is an example of the trade-off between good high frequency response and the avoidance of aliasing artifacts in digitizing systems. Laser printer
Figure 6 shows a plot of optical density vs gray level using the calibrated look-up table [see Fig. l(b)]. The relationship between input gray level and output optical density is quite linear for gray levels between 4 and 235 corresponding to optical densities 0.16-3.06. Beyond a gray level of 235 the film density saturates at optical density 3.06 due to the H-D curve characteristics of the film. The slope of the film density vs gray level curve can be changed via the software loaded look-up table and thus it is possible to directly manipulate the contrast of the original digital data at the time of printing (see Clinical Applications). An important consideration in any imaging device that utilizes an optical beam is the imaging spot characteristics. A knowledge of its properties can give a basic understanding of the flat field response and resolution capabilities of the system. A spot as defined here is the two-dimensional analog optical density distribution on film resulting from a digital impulse input to the laser printer. The spot will vary slightly with the amplitude of the input impulse and with the position of the spot on the film. At the periphery of the scanning field, the spot will be larger than at the center due to the oblique angle of the beam and the film. A spot taken from the center of a laser printer film was analyzed using a high resolution light microscope connected to a vidicon camera. Figure 7 shows a magnified view of the imaging spot along with the optical density profiles taken parallel and perpendicular to the beam traversal direction. It reveals that the spot is not circularly symetric but is elliptical with an approximate Gaussian distribution. The optimum spot shape in laser writing systems is often not circular due to the differences in motion of the spot in directions parallel and perpendicular to the scan direction. In the parallel direction, the spot motion is continuous and resolution is determined from spot size, spot shape, and response time of the acousto-optic modulator. In the perpendicular direction, the spot motion is discrete and resolution is determined by line spacing distance and aperture size and shape. The display aperture in the perpendicular direction must be large enough for proper raster blend, i.e. proper overlapping of adjacent spots. Banding artifacts can be created by improper blending of adjacent spots or when the beam is mispositioned from one line to the next adjacent line . The laser printer we tested utilizes a spot with full width at half maximum (FWHM) dimensions of 80.1 and 126.2 pm parallel and perpendicular to the scan direction respectively. The sampling distance in both directions is 80 pm. A spot analyzed at the periphery of an 8 x 10 in. film was seen to be only slightly different with a FWHM of 83.6pm (vs 80.1 pm) and 126.3 pm (vs 126.2 pm) parallel and perpendicular to the scan direction respectively. The flat field response of the laser printer was determined by measuring 100 random samples along the entire 8 x 10 in. film and computing the standard deviation of the measured optical densities. The deviation over the entire film did not exceed optical density 0.04. The results are given in Fig. 3. Noise
Fig. 7. Magnified view of imaging spot of laser printer with profiles taken parallel (1) and perpendicular (2) to the scan direction. The upper right figure shows the scale (distance from 1.0 to 1.1 is IOOpm).
values for the printer were obtained by taking 100 samples within a 2.0 x 2.0 cm2 area of the printed film and computing the mean and standard deviation of these measurements. The results of the noise measurement for the laser printer are shown in Fig. 4. Variations parallel to the scan direction arise mainly from fluctuations in the laser output intensity, as well as from instabilities in the acouto-optic modulator. Variations perpendicular to the scan direction are mainly due to positional errors when moving to the next adjacent line which result in improper overlap of adjacent spot distributions. The resulting MTF curve, shown in Fig. 8, obtained from the Fourier transform of the point spread function indicates that the MFT drops to 0.5 at a frequency of 4.6 c/mm. The results of the contrast frequency response parallel and perpendicular to the scan of the laser printer are shown in Fig. 9. The response at 3.0 c/mm is 0.75 in the parallel direction and 0.89 for the perpendicular direction. Note that in the perpendicular direction, the writing is discrete while in the parallel direction it is ,
0.4 0.3 0.2 0.1 0
Fig. 8. The modulation transfer function (MFT) for the laser printer in the direction parallel to the scan.
TO THE SCAN
TO THE SCAN ‘\ \
Fig. 9. Plot showing the relationship between the spatial frequency and the contrast frequency parallel and perpendicular to the scan direction for the laser printer.
Three line pairs per millimeter are easily resolvable on the processed film both parallel and perpendicular to the scan direction. Results of the spatial linearity tests indicate that there are slight distortions in the perpendicular direction (maximum deviation of 370 pm for a 20.3 x 20.3 cm film) and no detectable distortions in the direction parallel to the scan. This same test performed on line patterns from a multiformat video camera (MULTI-IMAGER 7 by Matrix Instruments) revealed a maximum deviation of 1490 pm for the same size film. Vertical distortions correspond to deviation in line scanning speed while horizontal distortions corresponds to nonlinearities in the optics. Special lenses (flat field f-theta lens) [4,7, 1I] used in the laser printer and scanner correct for nonlinearities normally present in conventional lenses. Figure IO shows linearity test results of the laser printer compared with the results obtained using the multiformat camera. The laser printer is clearly superior in terms of its spatial linearity to the video based printer.
The laser scanner and laser printer system are definitely major components in a digital-based radiology department. In addition, as a stand-alone system, it has clinical applications associated with contrast enhancement and patient dose reduction [12, 131. There are certain inherent advantages to having an X-ray image in digital form rather than analog than relate to the eye’s sensitivity to certain optical densities and optical density changes. Digital data obtained from the laser scanner can be subject to contrast enhancement and other digital image processing manipulations which exploit the
Fig. 10. Linearity test results for the Bottom: subtraction images of original printer shows minimum perpendicular right). The multiformat video printer
laser printer and a multiformat camera. Top: original line images. from original rotated 180” about the normal axis of the film. The laser distortion (no line residues) as the subtraction image shows (bottom subtraction (bottom left) shows significant perpendicular distortions.
SHIH-CHUNG B. Lo et al
:ig. 11, Dose reduction experiment. Radiographs of a rabbit skull taken with successively lower X-ray exposure techniques. (a) 50 kVp, 12 mAs, (b) 50 kVp, 6 mAs, (c) 50 kVp, 4 mAs, (d) 50 kVp, 2.75 mAs.
Fig. 12. Same radiographs
in Fig. 11 but digitized by the laser scanner then written a linear look-up table of the laser printer.
back onto film using
characteristics of the human visual system. Contrast enhancement is available on the laser printer system using software optical density transformation look-up tables. Figures 11 and 12 show a dose reduction experiment. Figure 11 shows radiographs of a rabbit skull taken with successively lower x-ray exposure techniques. The films were digitized and passed through the linear look-up table of the printer. Results are shown in Fig. 12. Preliminary observations of enhanced reduced dosage radiographs of a rabbit skull show that diagnostically acceptable images could be obtained using dose reduction factors of two to three in studies where quantum statistics were not limiting the resolution of the structures of interest. This system will also allow a certain percentage of overexposed radiographs to be diagnostically salvaged and hence decrease the number of retakes and thus reduce patient dose. Acknowledgements-We wish to thank Mr John Robert for assisting in the rabbit exposure experiments. We are grateful to the engineers and scientists at the Konishiroku Photo Ind. Co. Ltd Japan for providing hardware and software assistance and support.
REFERENCES I. 2. 3. 4. 5. 6. 7. 8. 9. IO. Il. 12. 13.
J. L. Johnson and D. L. Abernathy, Radiology 146, 851 (1983). C. Marceau, PACS for Medical Applications Part I, Proc. SPIE 318, 24 (1982). A. J. Duerinckx and E. J. Pisa. PACS for Medical Applications Part I, Proc SPIE 318, 9 (1982). J. N. Sanders, C. L. Cattell Jr, N. E. Bender and M. M. Tesic, Application qf Optical Inslrumentation in Medicine XII, Proc SPIE 454, 348 (1984). J. S. Urbach, T. S. Fish and G. K. Starkweather, Proc. IEEE 70, 597 (1982). P. M. Emmel, SPIE 222, 2 (1980). Digital Image Processing, pp. 22-23, 4&49. Prentice-Hall, New Jersey. K R. Castleman, H E. Johns and J. R. Cunningham, The Physics of Radiology, 3rd edn, p. 622. Thomas Springfield, Ill. (1978) A. D. Berg and J. P. Wheeler, Opt. Engng 15, 84 (1976). M L. Giger and K. Doi, Med. Phys. 11, 287 (1984). N Gramenopoulos and E. D. Hartfield, Appl. Opt. II, 2778 (1972). M Sonoda, M. Takano, J. Miyahara and H. Kato, Radiology 148, 833 (1983). M Ishida, K. Doi, L. N. Loo, C. E. Mets and J. L. Lehr, Radiology 150, 569 (1984). the Author-SHIH-CHUNG B. LO received his Ph.D. in Biomedical Physics Radiological Sciences, University of California, Los Angeles in 1986. Dr Lo has been imaging area for the past four years. His other contribution in this area is medical is currently employed in Philips Medical Systems Inc.. Shelton, Connecticut designing imaging.
in the Department of working in the medical image compression. He display console for MR
K. TAIRA received his B.S. degree from the University of California, Los Angeles m 1982 in Electrical Engineering. He is currently a Ph.D. candidate in the Biomedical Physics Division. Department of Radiological Sciences, University of California, Los Angeles working on the development of a computerized digital Pediatric Radiology Section.
About the Author-Rma’
J. MANKOVICH received his Ph.D. from the University of Illinois in 1982, and postdoctoral training in Biomedical Imaging at the University of Iowa and the University of California, Los Angeles. He is currently an Assistant Professor in the Department of Radiological Sciences at UCLA and has authored many publications on medical imaging and instrumentation.
About the Author-N~cHoL.ks
K. HUANG, D.Sc., is Professor and Chief of the Medical Imaging Division, Department of Radiological Sciences, University of California, Los Angeles. Dr Huang has been working in medical imaging for the past I7 years. His latest interest is the Picture Archiving and Communication System (PACS). He is currently in the process of implementing a totally digital pediatric radiology section at UCLA.
About the Author-H.
TAKEUCHI Ph.D. has been a postdoctoral fellow in the Division of Medical Imaging, Department of Radiological Sciences, University of California, Los Angeles for the past two years. He is currently on leave of absence from Konishiroku Photo Ind. Co. Ltd. Tokyo, Japan. His research interest is in laser scanner and printer on radiological films. His other interest is in dual energy digital radiography.
About the Author-HrRosw1