A novel RBF-based predictive tool for facial distraction surgery in growing children with syndromic craniosynostosis.

PURPOSE: Predicting changes in face shape from corrective surgery is challenging in growing children with syndromic craniosynostosis. A prediction tool mimicking composite bone and skin movement during facial distraction would be useful for surgical audit and planning. To model surgery, we used a radial basis function (RBF) that is smooth and continuous throughout space whilst corresponding to measured distraction at landmarks. Our aim is to showcase the pipeline for a novel landmark-based, RBF-driven simulation for facial distraction surgery in children. METHODS: An individual's dataset comprised of manually placed skin and bone landmarks on operated and unoperated regions. Surgical warps were produced for 'older' monobloc, 'older' bipartition and 'younger' bipartition groups by applying a weighted least-squares RBF fitted to the average landmarks and change vectors. A 'normalisation' warp, from fitting an RBF to craniometric landmark differences from the average, was applied to each dataset before the surgical warp. The normalisation was finally reversed to obtain the individual prediction. Predictions were compared to actual post-operative outcomes. RESULTS: The averaged change vectors for all groups showed skin and bone movements characteristic of the operations. Normalisation for shape-size removed individual asymmetry, size and proportion differences but retained typical pre-operative shape features. The surgical warps removed the average syndromic features. Reversing the normalisation reintroduced the individual's variation into the prediction. The mid-facial regions were well predicted for all groups. Forehead and brow regions were less well predicted. CONCLUSIONS: Our novel, landmark-based, weighted RBF can predict the outcome for facial distraction in younger and older children with a variety of head and face shapes. It can replicate the surgical reality of composite bone and skin movement jointly in one model. The potential applications include audit of existing patient outcomes, and predicting outcome for new patients to aid surgical planning.

Three-dimensional MRI of the male urethrae with implanted artificial sphincters: initial results.

The aim of this study was to develop a method for simultaneous 3D visualization of a new type of artificial urethral sphincter (AUS) and adjacent urinary structures. Serial MR tomograms were acquired from seven men after AUS implantation. 3D reconstruction was performed by thresholding original (positive) and inverted (negative) image intensity and by subsequently fusing positive and negative images. Results show that the bladder, cuff and balloons of the AUS of originally high intensity were imaged in 3D by thresholding the positive datasets. The urethrae and corpora cavernosa penis of originally low intensity were displayed in 3D by thresholding the negative datasets. Fusion of the positive and negative datasets allowed simultaneous visualization of the AUS complex and adjacent urinary structures. All the structures of interest were also clearly seen by interactive multiplanar reformatting. Coronal tomographic datasets provided better 3D and reformatted 2D images than sagittal and transverse datasets. This technique offers a simple means for evaluating the complex urethral anatomy and the AUS, and has potential for improved 3D visualization of many other complex morphological and pathological conditions.

Dynamic three-dimensional color Doppler ultrasound of human fetal intracardiac flow.

OBJECTIVES: To develop dynamic three-dimensional ultrasound techniques for prenatal imaging of the intracardiovascular flow as well as the cardiovascular structure to address difficulties in assessing the spatially complex hemodynamics and morphology of the fetal heart. METHODS: Gray-scale and color (velocity) Doppler echocardiography were performed on 12 fetuses to provide serial anatomical and rheological tomograms which were spatially registered in three dimensions. Using a second ultrasound machine simultaneously, spectral Doppler ultrasound was performed to record umbilical arterial waveforms, thus providing the temporal (fourth) dimension in terms of the cardiac cycle and facilitating removal of motion artifacts. RESULTS: Acquisitions were successful in eight of 15 attempts. Imaging of the flow of blood in four dimensions was achieved in six of the eight datasets. In one case with complex cardiac malformations, three-dimensional reconstructions at systole and diastole offered dynamic diagnostic views not appreciated on the cross-sectional images. CONCLUSIONS: Our novel technique has made possible the prenatal visualization of the spatial distribution and true direction of intracardiac flow of blood in four dimensions in the absence of motion artifacts. The technique suggests that diagnosis of cardiac malformations can be made on the basis of morphological and hemodynamic changes throughout the entire cardiac cycle, offering unique and significant information complementary to conventional techniques. Further work to integrate the several non-purpose-built machines into a single system will improve the rate of acquisition of data, and may provide a new means of imaging and modeling structure and hemodynamics, not only for the fetal heart but for many other moving body parts.

Online motion-gated dynamic three-dimensional echocardiography in the fetus--preliminary results.

The aim of this study was to visualise the fetal heart in dynamic three dimensions (4-D) during an ultrasound (US) scan (online), rather than after (offline). With special pairing and sequential setting to minimise interference between two scanners, umbilical arterial Doppler waveforms (UADWs) from one scanner were used as an online motion gating source to trigger simultaneous 3-D cardiac structural data acquisition by another. Of 25 data sets from 10 fetuses, 18 were acquired in 15 to 30 s per set with > or = 50% Doppler waveforms efficiently converted to triggering signals. Of 15 valid 4-D data sets, 10 were reconstructed in 2 to 20 min, compared to over 2 h previously reported (mainly for offline gating). Fine structures (including chordae tendinae and trabecular muscles) were depicted in six sets. The main problems in degrading 4-D images were extensive shadowing (6) from bony structures during rigid mechanical scanning, and random motion artefacts (6) from prolonged setting-up time with a complex combination of several systems. Integration of these systems is, therefore, recommended.

Conversion of umbilical arterial Doppler waveforms to cardiac cycle triggering signals: a preparatory study for online motion-gated three-dimensional fetal echocardiography.

To remove motion artefacts, a device was built to convert "noisy" umbilical arterial Doppler waveforms (UADWs) from an ultrasound (US) system into sharp ECG R-wave-like cardiac cycle triggering signals (CCTSs). These CCTSs were then used to gate a simultaneous (online) 3-D acquisition of sectional fetal echocardiograms from another US system. To test the conversion performance, a study was carried out in sheep fetal twins. Pulmonary arterial flow waveforms (PAFWs) from implanted probes were traced, in the meantime, to determine the reference cardiac cycle. Interference caused by running the two nonsynchronised US systems was controlled to three degrees (not-noticeable, moderate, and severe), together with high (> or = 40 cm/s) and low (< 40) flow velocities on UADWs. The conversion efficiency, assessed by the percentage of UADWs converted into CCTSs, was in the range of 83% to 100% for not-noticeable and moderate interference, and 0% to 71% for severe interference. The triggering accuracy, assessed by [(time lag mean between the onsets of PAFWs and corresponding CCTSs) -- (its 99% confidence level)] / the mean, was 90% to 96% for the not-noticeable interference high- and low-flow groups and for the moderate interference high-flow group; 19% to 93% for the moderate interference low-flow group; and from not obtainable up to 90% for the severe interference groups. The results show that UADWs can be used as a satisfactory online motion-gating source even in the presence of moderate interference. The major problems are from severe interference or moderate interference with low-flow velocity, which can be minimised/eliminated by the integration of the individual systems involved.

Simultaneous use of two ultrasound scanners for motion-gated three-dimensional fetal echocardiography.

The aim of this study was to determine whether or not simultaneous use of an additional Doppler transducer could provide sufficient cardiovascular motion information without significantly interfering with three-dimensional (3-D) cardiac structural data acquisition by a primary two-dimensional (2-D) transducer. To determine sources of interference, paired transducers were activated alternatively and simultaneously in and out of a water bath, with and without electrical insulating and electromagnetic shielding. To determine factors affecting interference, pairs were tested on a phantom with different separating distances and angles between paired ultrasound (US) beams and under different 2-D depths and Doppler scales. Results show that the dominant source of interference is acoustic cross talk. The severity was mainly affected by transducer pairing and by separating distances and angles, and the pattern by display settings. With optimised settings, sufficient structural and motion data were obtained simultaneously in 9 of 12 fetal hearts, and detailed 3-D views could be reconstructed free of motion artefacts, confirming the feasibility of using the method for motion-gated 3-D fetal cardiac imaging. New scanner design strategy was then proposed.

Novel technique for three-dimensional visualisation and quantification of deformable, moving soft-tissue body parts.

BACKGROUND: Three-dimensional (3D) imaging of delicate, moving soft-tissue body parts is very difficult. Our understanding of the muscles that control lip movements is based largely on histological and cadaveric studies, which provide scant information about dynamic morphology. Our aim was to develop an innovative scanning technique for the imaging and reconstruction of dynamic orofacial morphology by use of 3D and four-dimensional (4D, ie, 3D plus time) ultrasonography. METHODS: Four volunteers (including one patient) underwent ultrasonography with 3D/4D imaging systems. To avoid deformation of the delicate orofacial structures, a water bath with an acoustic window was devised. The orofacial part was immersed in the bath throughout scanning, and a timer was used to synchronize lip movements with the 4D scan. FINDINGS: 4D views showed the functional differences in superficial and deep muscle groups of the lips, and clearly showed the changes occurring with movement of the lips and mouth. In the patient, a pathological layer and its extension corresponding to surface malformation were clearly identified. INTERPRETATION: We have developed a prototype device that has made possible 3D and 4D examination of orofacial anatomy and function. With further refinement of the device and improvement in 4D acquisition timing, this technique may offer a new way of dynamically imaging and quantifying many soft-tissue parts in 3D without deforming structure or disturbing function.

Validation of computer-assisted manufacture of titanium plates for cranioplasty.

We have constructed 300 titanium cranioplasty plates, over 150 cases using a computerised technique, the remainder by external impression. The clinical follow-up of these cases over 8 years has shown consistently good results that justify our simple low-cost method of manufacturing these plates. Both techniques require the provision of a model on which to construct the plate. In the traditional technique, an approximate model is derived from the resected bone or a direct impression of the defect over the patient's scalp. Using the computerised technique, a more accurate model of the defect and the surrounding bone is milled in polyurethane foam from cross-sectional computerised tomographic (CT) scans. Sheet titanium is pressed to shape from a design outlined on a counterdie. The subsequent stages of the plate construction are then the same for both methods. This study describes the stages of the model manufacture, the validation of its accuracy and the plate construction that follows. Use of the computerised method has resulted in a reduction of errors, enabling the manufacture of a smaller plate than was possible previously. It has also enabled design changes through the achievement of greater accuracy in fit.

Three-dimensional morphometry in ultrasound.

The clinical use of three-dimensional (3D) ultrasound has rapidly spread to many specialities over the last ten years. The reason is easy to see, namely that single two-dimensional (2D) scans are often difficult to interpret and the mental correlation of multiple 2D scans to form a 3D image of anatomical morphology is taxing and uncertain. The rapid development of techniques for the realtime tracking of the spatial position and orientation of ultrasound probes and the development of computer graphics techniques for the presentation of anatomical images have made 3D ultrasound a realistic diagnostic tool. The authors describe the range of methods of data acquisition and display and provide illustrations of some current clinical applications.

Three-dimensional analysis techniques--Part 1: Three-dimensional soft-tissue analysis of 24 adult cleft palate patients following Le Fort I maxillary advancement: a preliminary report.

The three-dimensional, facial soft-tissue changes of 24 patients with various cleft types following transpalatal Le Fort I osteotomy were measured using laser scanning techniques, radial measurements, and a color millimetric scale. There was a varying degree of midface retrusion in the different cleft groups, and a very similar pattern of retrusion over the nasal complex. Each group of patients showed a varying degree of relapse postsurgically, but there was a failure in all the cleft groups to correct the lack of nasal projection.

Three-dimensional analysis techniques--Part 2: Laser scanning: a quantitative three-dimensional soft-tissue analysis using a color-coding system.

New methods for measuring and averaging three-dimensional soft-tissue morphology and change from laser scans using a color millimetric scale are described. The techniques were employed to measure facial differences between a group of Class I skeletal males and females. The surgical change in one patient following bimaxillary surgery is also illustrated. The combination of the laser scanning technique and the new color coding system probed to be a simple, noninvasive, effective, and easily interpreted method for measuring three-dimensional soft-tissue differences and change across the facial complex.

Three-dimensional analysis techniques--Part 3: Color-coded system for three-dimensional measurement of bone and ratio of soft tissue to bone: the analysis.

A new color-coded method of illustrating three-dimensional changes in the bone and the ratio of soft tissue to bone movement is described. The technique is illustrated by superimposing preoperative and 1-year postoperative CT scans of three patients following bimaxillary surgery. The method has proved to be a very simple, effective, and readily interpreted method of quantifying both bone and the ratio of movement of the overlying soft tissues across the face following surgery.

Three-dimensional analysis techniques--Part 4: Three-dimensional analysis of bone and soft tissue to bone ratio of movements in 24 cleft palate patients following Le Fort I osteotomy: a preliminary report.

The three-dimensional changes in the bone and the ratio of soft tissue to bone movement were investigated in a group of 24 cleft palate patients following Le Fort I osteotomy. CT scans were taken for each patient preoperatively and 1 year postoperatively. The scans were superimposed, radial measurements calculated, and the changes illustrated by two separate color scales. In all of the groups, there was a fairly consistent pattern of movement over the mandible. The soft tissues moved in a 1.25:1 ratio over the chin and canine regions, and reduced to 1:1 over the body. In the maxilla, there was a 1:1 movement in the midline increasing to 1.25:1 bilaterally over the alar bases for both the bilateral clefts and clefts of the secondary palate groups. In the unilateral cleft group, however, there was a greater degree of movement over the cleft than over the noncleft side.

The use of three-dimensional techniques in facial esthetics.

The three-dimensional nature of beautiful faces is analyzed and beauty is investigated by means of optical-surface scanning. This noninvasive technique is described and illustrated and its value in the assessment of beauty noted. Forty men and 40 women with a normal Class I skeletal pattern and a Class I occlusion were scanned and an average face was obtained for each group. The averages were compared with those derived from a group of 9 men and 15 women employed as professional models and the differences were noted. A group of normal Asian teenagers were scanned to investigate ethnic differences. The groups of professional models were further analyzed to see whether they measured up to the "golden proportions" described by the ancient Greeks. The groups did not fit the "golden proportions" and they represented instead a range of malocclusion and a wide range of cephalometric values.

A three-dimensional soft tissue analysis of fifteen patients with Class II, Division 1 malocclusions after bimaxillary surgery.

A three-dimensional soft tissue study of the results of surgery in a group of 15 women with Class II, Division I malocclusions after orthognathic surgery was performed with laser scans. A group of 30 women with Class I malocclusions ages between 19 and 25 years were used as controls. Laser scans were taken before surgery, 3 months after surgery, and at least 1 year after retention. The skeletal 2 patients were shown to have a narrowing of the face over the maxillary complex, checks, the nose, as well as around the alar bases, the so called "adenoid facies." There was also the expected mandibular deficiency. The effects of the bimaxillary surgery were not simply confined to the maxilla and the mandible, with soft tissue changes extending as far as the outer canthi of the eyes. There was very little relapse in the group as a whole from the third month to 1 year after surgery. This technique has proved to be a simple noninvasive method of measuring three dimensionally. It has proven to be a very useful tool in auditing surgical outcome and measuring surgical relapse.

A three-dimensional analysis of bone and soft tissue to bone ratio of movements in 17 Skeletal II patients following orthognathic surgery.

The three-dimensional changes in the bone and the ratio of soft tissue to bone movement were investigated in a group of 17 Skeletal II patients following orthognathic surgery. CT scans were taken for each patient pre-operatively and 1 year post-operatively. The scans were superimposed, radial measurements calculated, and the changes illustrated by two separate colour scales. There was a constant ratio of movement over the maxillae with the central part of the upper lip being moved in a 1:1 ratio, increasing to a 1.25:1 ratio over the canine regions and 1.5:1 ratio over the paranasal areas. In the mandible there was a constant ratio of 1.25:1 over the chin, mentalis, and canine regions bilaterally. The ratio reduced to 1:1 over the body of the mandible.

Registration of 3-D head surfaces using multiple landmarks.

A mathematical procedure based on Newton's method is described that enables surface measurements to be registered, or normalized, with respect to spatial position, orientation, and, optionally, scale in three dimensions. An operator is required to identify homologous landmarks on the computer graphics images of surfaces to be registered. In this application, where the method is used to measure changes in facial shape, these landmarks are restricted to parts of the surface that have remained unchanged between the surfaces to be registered. Error in the registration of landmarks is minimized in a least-squares sense; hence multiple landmarks are favored to minimize the effect of individual errors produced by the measuring system and the operator. Examples are presented using measurements of the head taken with an optical surface scanner and a conventional X-ray computed tomography scanner.

Three-dimensional visualization of data on human anatomy: diagnosis and surgical planning.

A system is described which produces displays of anatomical surfaces from sets of X-ray computed tomography (CT), magnetic resonance imaging (MRI) and ultrasonographic scans (US). The displays are created to show the three-dimensional character of the internal and external anatomy. The images may be manipulated on the screen to simulate dissection of the three-dimensional object they represent. Thus it is possible to increase the diagnostic value of the original data and to plan surgery by simulation. To allow long-term studies on the human face for surgical planning and assessment a non-hazardous optical scanning system has been devised. The display system also produces data to drive a numerically controlled milling machine for the production of models, prostheses and implants.

The analysis of profiles using curvature analysis.

The difficulties of localizing landmarks using standardized lateral skull radiographs has been acknowledged. A method is described for producing an objective way of identifying landmarks on the facial profile leading to a useful segmentation and quantitative description of the contours and features of the face. The method uses scale space filtering techniques and curvature analysis, first employed in pattern recognition. The method has been used on two groups: a random sample of twelve-year-old females and a sample of 10 patients with a normal facial morphology who had cephalometric X-rays taken at 5, 9, 13, 16, and 20 years. It demonstrated that the shape of each of the curves is similar in the first group except in the mouth region. The growth study produced meaningful data on the growth of the face.