An optimised radial basis function algorithm for fast non-rigid registration of medical images.

The registration of multi-modal medical image data is important in the fields of image guided surgery and computer aided medical diagnosis. Registration accuracy is of utmost importance in both fields, however in the former, the speed of registration is equally important. In this paper, we present a point-based 'fast' non-rigid registration algorithm which exhibits significant speedups as compared to the non-optimised equivalent algorithm. Additionally, we make use of the parallel nature of the graphics processing unit (GPU) of the video adapter card of a standard PC to gain further speedups. The algorithm achieved sub-second performance when tested on the registration of MR with CT image data of size 256(3).

Real-time rendering of radially distorted virtual scenes for endoscopic image augmentation.

This paper presents a method for rendering radially distorted virtual scenes in real-time using the programmable fragment shader commonly found in many main stream graphics hardware. We show that by using the pixel buffer and the fragment shader, it is possible to augment the endoscopic display with distorted virtual images.

Recording forces exerted on the bowel wall during colonoscopy: in vitro evaluation.

A novel system for distributed force measurement between the bowel wall and the shaft of a colonoscope is presented. The system, based on the piezoresistive method, involves the integration of soft miniature transducers to a colonoscope to enable a wide range of forces to be sensed. The attached sensing sheath does not restrict the propulsion of the colonoscope nor notably alter its flexibility. The addition of the sensor sheath increases the colonoscope diameter by 15-20% depending on the type of the colonoscope (adult or paediatric). The transducer's accuracy is +/-20 grammes if it is not subjected to extensive static forces. Under large static force conditions the errors may increase to +/-50 grammes. The tactile force measuring sensors have provided preliminary results from experiments on a model of the large bowel. The force measurements confirm the predictions on the location and magnitude of the forces and that most of the forces are exerted whilst the instrument is looping.

Colonoscopy aided by magnetic 3D imaging: assessing the routine use of a stiffening sigmoid overtube to speed up the procedure.

There are not enough trained colonoscopists to cope with the present recommended number of examinations required for diagnostic and surveillance purposes. If colorectal cancer screening is to be introduced, endoscopic examination of the large bowel needs to be easier to learn and significantly quicker to carry out. The 'Bladen system', first described in 1993, is a non-radiological method of visualising the path of the endoscope, using magnetic drive coils under the patient and a chain of sensors along the biopsy channel of the instrument. In 1998, results were published using a novel computer graphics system (the RMR system), in which a much more realistic image of the endoscope could be produced using the stored positional data from the Bladen system. The RMR system has been further refined to allow, for the first time ever, accurate measurement of the effect of the passage of a colonoscope along the bowel on the lengths of different segments of the large intestine. The results obtained in 232 patients undergoing colonoscopy are analysed. In 77 of the patients, a stiffening overtube is used to splint the sigmoid colon once the endoscope is at or beyond the splenic flexure. The mean time taken to pass the colonoscope across the transverse colon is significantly shorter (p < 0.001) when an overtube is used, despite it resulting in significant lengthening of the transverse colon. The routine use of a stiffening overtube can be expected to reduce the total procedure time by between 10 and 20%.

Colonoscopy aided by magnetic 3D imaging: is the technique sufficiently sensitive to detect differences between men and women?

Colonoscopy tends to be more difficult to perform in women. Women also experience more pain during flexible sigmoidoscopy, and the mean insertion distance of the instrument is less than in men. The 'Bladen system', first described in 1993, is a non-radiological method of continuously visualising the path of the endoscope using magnetic drive coils under the patient and a chain of sensors up the biopsy channel of the instrument. In 1998, results were published that used a novel computer graphics system (the 'RMR system'), in which a much more realistic endoscope could be produced using the stored positional data from the Bladen system. The RMR computer graphics system has been further refined to enable measurement of the anatomical lengths of different parts of the large intestine to an accuracy of greater than 5 mm. The system is used to analyse the results obtained in 232 patients undergoing a total colonoscopy. In women, the colonoscope tends to form loops in the sigmoid colon more readily than in men (p < 0.05). When the first 50 cm of the endoscope are inserted for the first time, the tip passes either up to or beyond the splenic flexure in 40/116, or 34.5%, of males, compared with 24/117, or 20.5%, of females (p = 0.0137). It is demonstrated that women have longer transverse colons than men, and the differences are especially apparent when a stiffening tube is used to splint the left side of the colon (p < 0.0001). The possible relevance of these observations to biomedical engineers and those manufacturing and assessing prototype endoscopes is discussed.

Non-radiological technique for 3D imaging of intestinal endoscopes: computerised graphical 3D representation of endoscope and skeleton.

Colorectal cancer is a common malignancy but as yet there is no agreement regarding the optimal method for screening. Colonoscopy is theoretically the investigation of choice. The examination can, however, be difficult to perform and the average trainee requires at least 200 supervised examinations to become proficient. Colonoscopy takes on average about half an hour per patient and sedation is normally required because of painful instrument looping. The authors previously developed a non-radiological method of visualising the path of the endoscope using magnetic drive coils under the patient and a chain of sensors in the biopsy channel of the instrument. The computer-generated grey-scale images produced in real time were deemed unsatisfactory and the anatomical markers confusing. A new computer graphics system is described in which a much more realistic endoscope and, if necessary, skeleton can be produced. The wire-frame octagonal representation should help in the detailed analysis of colonoscopy using existing endoscopes and aid in future computer design and testing of novel instruments incorporating worm or snake-like properties.

IsoStar: a library of information about nonbonded interactions.

Crystallographic and theoretical (ab initio) data on intermolecular nonbonded interactions have been gathered together in a computerised library ('IsoStar'). The library contains information about the nonbonded contacts formed by some 250 chemical groupings. The data can be displayed visually and used to aid protein-ligand docking or the identification of bioisosteric replacements. Data from the library show that there is great variability in the geometrical preferences of different types of hydrogen bonds, although in general there is a tendency for H-bonds to form along lone-pair directions. The H-bond acceptor abilities of oxygen and sulphur atoms are highly dependent on intramolecular environments. The nonbonded contacts formed by many hydrophobic groups show surprisingly strong directional preferences. Many unusual nonbonded interactions are to be found in the library and are of potential value for designing novel biologically active molecules.