Problems of the Third Dimension

Path. Res. Pract. 185,594-597 (1989)

Problems of the Third Dimension W.F. Whimster Department of Morbid Anatomy, King's College School of Medicine and Dentistry, London, UK

SUMMARY The problems facing a pathologist or anatomist who wishes to embark on computerassisted reconstruction of structures seen in serial light microscope sections are reviewed. They are illustrated by comparing a reconstruction of a bronchial gland made by cutting out polystyrene sheets with models generated by four computer-assisted systems, i.e. the IBAS 2000 system, the SSRCON (MRC) system, the AT- Videoplan system and the CHO (Cookson, Holman, Dykes) system. It is obvious that computer-assistance cannot solve the preparation problems of three-dimensional reconstruction (30R) and that choosing a computer-assisted system is fraught with difficulties. It is recommended that intending purchasers ofcomputer-assisted 30R systems prepare material in advance to tryout on the systems they are considering.

Introduction Pathologists and anatomists dealing with two dimensional histological preparations of organs and tissues often wish that they could have a three dimensional view of the structures seen in their sections. The advent of computers into three dimensional reconstruction (3DR)1 appeared to make this more of a routine possibility than the laborious model making with wax or plywood that preceded it2 . Unfortunately many of the previous problems, such as tissue acquisition, preparation and registration, did not come within the scope of computerisation, and 3D modelling with computer assistance has its own problems. The present author already had serial, formalin fixed, alcian bluelhaematoxylin and eosin stained, light microscope sections of human bronchi, from 104 of which a scale model of a tracheobronchial gland had been reconstructed from polystyrene sheet of appropriate thickness (Fig. 1). This showed the distribution of ciliated epithelium (identical with the bronchial epithelium), collecting duct, mucous and serous cell lined epithelium. As it was intended to purchase a computer-assisted 3DR system, this material was used to assess the systems available and to identify the problems facing a pathologist or anatomist who wished to do likewise but who did not have suitable: test material. 0344-0338/89/0185-0594$3.50/0

Methods The literature for 1983-1986 was searched by Datastar (Radio Suisse Ltd) and for 1986-1988 through Current Contents (Life Sciences) using the descriptors "dimensions(s)" and "reconstruction(s)" . Access was obtained to four systems: IBAS 2000 (in the author's laboratory, supplied by Zeiss Oberkochen, UK, with programs by Kontron), SSRCON (Medical Research Council) (courtesy of Professor Scheuer and Steve Howe, Royal Free Hospital Medical School, London), AT-Videoplan (courtesy of Zeiss Oberkochen, UK), and the CHD system (courtesy of John Cookson, John Holman and Eric Dykes, .London Hospital medical College, London). The details of the hardware and software are not relevant here but can be obtained from those acknowledged. With much help from those mentioned, the bronchial gland data were inputted into and models created by each system. The models created on the VDUs were compared with the polystyrene "gold standard", photographed and videotaped. The general problems encountered with each system were recorded and used to· make a checklist with which to test further systems and for pathologists or anatomists without previous experience in computer assisted 3DR.

© 1989 by Gustav Fischer Verlag, Stuttgart

Problems of the Third Dimension· 595

Fig. 3. Computer model of the gland in Figure 1 generated by the AT-Videoplan system.

Fig. 1. The model created by cutting out, colouring (black ciliated cells; green = collecting duct cells; blue = mucous cells; Red = serous cells) and stacking polystyrene sheets (equivalent to 7 micrometers thickness) to represent the 104 serial sections of a gland in the 9th generation down the inferior Iingular airway.

Fig. 4. Computer model of the gland in Figure 1 generated by the CHD system (solid yellow = lumen; other colours in transparent mode; purple = ciliated duct; dark blue = ciliated cells of bronchus).

Fig. 2. Computer model of the gland in Figure 1 generated by the SSRCON system.

596 . W. F. Whimster

Results The literature contained over 170 relevant citations since 1972, of which the most useful was that ofHuijsmans et al.3 who reviewed 58 software packages, using an assessment system that included 173 items. Use of the systems revealed one fundamental difference between the CHD system and the others. The data for the CHD system had to be entered for the whole of each individual structure separately, i.e., the outline within each section of the individual structure had to be identified by the operator through the series of serial sections, giving rise to what we have called "vertical" data entry. With the other systems all the data on a serial section, i.e., for all the outlines digitised on that section, were entered before proceeding to the next section. We called this "horizontal" data entry. With the latter the operator could use the model to decide the connections between individual tubules. Figures 2-4 show examples of the models created by each system. Each system was found to have its own problems and advantages. IBAS 2000. This system used IBAS 2000 hardware but the 3D program had been written for the Videoplan. Its main limitation was lack of memory (24K) so that even with a simple tubular structure (the main duct) only about 50 serial sections could be entered, after which the system crashed without warning. An advantage was that the data could be converted into grey levels and an artificially coloured model created.. SSRCON. The disadvantage was that the models were rather "flat" and lacking in perspective (see discussion). This system was, however, versatile and had the advantage of facilities to produce stereopairs, yellow-green images for viewing through red-green spectacles, and a variety of colours and modes of presentation. Measurements were available but were not tested in the presen,t context. A T- Videoplan. The main disadvantages were: a) although five different components on a serial section (e.g. the lumen, ciliated, collecting, mucous and serous duct outlines) could be entered separately there were only three colours available to show these components. b) Reconstruction of the whole structure (104 sections) took about four minutes and could not be aborted. On the other hand the model had good perspective and by using "slabs" (of thickness prescribed by the operator) gave a good idea of how the drawings and the data entry themselves were out of alignment. A measurement facility was available which appeared to work but could not be checked out with the present material. This system is being upgraded at present. CHD. The main disadvantages with this system was that data entry took much longer. Conversion of the data for each structure into the model was laborious, taking several programs. The advantage was that many facilities were available. Model building could be aborted. Models could be stored and quickly retrieved without recreation. Individual tubules (entered vertically) could be studied separately. Tiling, surfacing, highlighting and perspective alteration were all available. This system produced the most beautiful models, but it remains to be checked out

whether they were more realistic than the AT-Videoplan ones in which the input defects were clearly visible. Discussion Literature

The literature search produced a large number of publications in which computer-assisted 3DR had been used or computer-assisted 3DR problems, such as registration, had been addressed. Two problems stood out. Firstly, the computer hardware and software were rarely described in such a way that the reader could have obtained them and repeated the work himself. Secondly, although computers produce their models in a 2D format on a VDU screen, in few papers were the models reproduced in such a way that the reader could adequately consider the interpretations of the authors, even if colour illustrations were used. The problem of presentation of 3DR results has yet to be adequately addressed. Entry into Three-Dimensional Reconstruction

The pathologist or anatomist who knows little about computers may think that the way to get into computerassisted 3DR is to talk to the manufacturers. Unfortunately, although manufacturers are very willing to discuss, demonstrate and sell their systems, it is difficult to decide whether a system will fulfil one's needs without having some material of one's own to tryout on the system. Preparing such material may be very laborious and lead one into the series of problems associated with tissue acquisition, serial sectioning and registration. It is also

Table 1. Data entry checklist Scale entry Registration points Horizontal or vertical entry Digitising tablet: drawing, dotting Automatic contouring Channels for components Correction: at time of entry, later RAM available Data processing

Table 2. Model viewing checklist Reconstruction menus Reconstruction time Abort facility Colours for components Magnification Screen position and rotation (x, y, z) Perspective Lighting Report Image storage

Problems of the Third Dimension . 597 Table 3. Presentation checklist Printer Plotter Stereo pajrs Red green Photography Videotape

Table 4. Huijsmans list for international cooperation. (Abstract for International Conference on 3-D Image Processing in Microscopy, Gief~en, West German. March 9-11 1988) -

Parallel serial section sources Input routes Realignment and deformation correction policies Functions demanded by different disciplines Computer representations and their formal descriptions agreed upon Representation conversion routines developed Numerical calculations and interfaces to statistical packages Needs for special hardware architectures for clinical applications

essential to collaborate with a computer scientist to assess the technical aspects of ,the equipment and whether the price is reasonable, not only in the light of the immediate project but for future projects. The checklists of Huijsmans et aJ.3 are too long and heterogeneous for a pathologist or anatomist, but short lists of questions in the areas of data entry, model

construction, and presentation may be helpful (Tables 1-3). Future Development Huijsmans has listed eight areas for international coperation towards standardisation (Table 4). However, what the pathologist or anatomist requires for the future is fast and powerful hardware and comprehensive userfriendly software, both with adequate instruction manuals. The hardware may be approaching uniformity with the fast IBM-compatible machines and hard discs with hundreds of megabytes of storage, but it seems likely that it will take much longer for the software packages to be easy to select. Much development is still needed and the pathologist and anatomist will continue to need professional computer advice. Nevertheless the best safeguard against unsuitable equipment is real material with which to test what it can do. References 1 Ware RW, Lo Presti V (1975) Three-dimensional reconstruction from serial sections. In: Bourne GH, Danielli JF, Jeon KW (Eds.) International Review of Cytology, 40, 325-440 2 Gaunt WA (1971) Microreconstruction. Pitman Medical, London 3 Toward computerized morphometric facilities: a review of 58 software packages for computer-aided three-dimensional reconstruction quantification and picture generation from parallel serial sections. Anat Rec (1986) 216: 449-470 The references produced by the literature searches are available from the author on receipt of a photocopying and postage charge of £5 sterling.)

Received March 31, 1989 . Accepted in revised form July 19, 1989

Key words: Third dimension - 3-D reconstruction W. F. Whimster, Dept. of Morbid Anatomy, King's College School of Medicine and Dentistry, Denmark Hill, London SE5 8RX,

U.K.