Accurate Measurement of Cartilage Morphology Using a 3D Laser Scanner. In: Beichel RR, Sonka M, editors. Computer Vision Approaches to Medical Image Analysis. Berlin: Springer Berlin Heidelberg; 2006. pp. 37-48. [DOI: 10.1007/11889762_4]

Evaluation of the geometric accuracy of computed tomography and microcomputed tomography of the articular surface of the distal portion of the radius of cats

OBJECTIVE

To evaluate accuracy of articular surfaces determined by use of 2 perpendicular CT orientations, micro-CT, and laser scanning.

SAMPLE

23 cat cadavers.

PROCEDURES

Images of antebrachia were obtained by use of CT (voxel size, 0.6 mm) in longitudinal orientation (CT_LO images) and transverse orientation (CT_TO images) and by use of micro-CT (voxel size, 0.024 mm) in a longitudinal orientation. Images were reconstructed. Craniocaudal and mediolateral length, radius of curvature, and deviation of the articular surface of the distal portion of the radius of 3-D renderings for CT_LO, CT_TO, and micro-CT images were compared with results of 3-D renderings acquired with a laser scanner (resolution, 0.025 mm).

RESULTS

Measurement of CT_LO and CT_TO images overestimated craniocaudal and mediolateral length of the articular surface by 4% to 10%. Measurement of micro-CT images underestimated craniocaudal and mediolateral length by 1%. Measurement of CT_LO and CT_TO images underestimated mediolateral radius of curvature by 15% and overestimated craniocaudal radius of curvature by > 100%; use of micro-CT images underestimated them by 3% and 5%, respectively. Mean ± SD surface deviation was 0.26 ± 0.09 mm for CT_LO images, 0.30 ± 0.28 mm for CT_TO images, and 0.04 ± 0.02 mm for micro-CT images.

CONCLUSIONS AND CLINICAL RELEVANCE

Articular surface models derived from CT images had dimensional errors that approximately matched the voxel size. Thus, CT cannot be used to plan conforming arthroplasties in small joints and could lack precision when used to plan the correction of a limb deformity or repair of a fracture.

Suitability of Using the Hamate for Reconstruction of the Finger Middle Phalanx Base: An Assessment of Cartilage Thickness

Background

Osteochondral grafts are indicated for reconstructing the finger middle phalanx base when there is greater than 50% involvement of the articular surface and significant comminution. This study aims to compare the cartilage thickness of the distal surface of the hamate to the finger middle phalanx base to assess its suitability as an osteochondral graft.

Methods

A 3-dimensional laser scanner and computer modelling techniques were utilized to determine the cartilage thickness of the distal surface of the hamate, and finger middle phalanx base using cadaver specimens. The mean, maximum, and coefficient of variation (CV%; a measure of uniformity of cartilage distribution), as well as cartilage distribution maps were determined.

Results

The mean cartilage thickness of the hamate was 0.73 ± 0.08 mm compared to the average mean thickness of the finger middle phalanx base of 0.40 ± 0.12 mm. The maximum cartilage thickness of the hamate was 1.27 ± 0.14 mm compared to the average maximum of the finger middle phalanx base of 0.67 ± 0.14 mm. The CV% of the hamate was 27.8 ± 4.2 compared to the average CV% for the finger middle phalanx base of 26.6 ± 8.1. The hamate and finger middle phalanx base have maximum areas that were most frequently at or spanning the median ridge; however, this was more consistently observed with the hamate.

Conclusion

The distal surface of the hamate is a suitable osteochondral graft with respect to cartilage thickness and distribution providing sufficient cartilage for reconstruction of the finger middle phalanx base.

A novel approach for intra-operative shape acquisition of the tibio-femoral joints using 3D laser scanning in computer assisted orthopaedic surgery

BACKGROUND

Image registration (IR) is an important process of developing a spatial relationship between pre-operative data and the physical patient in the operation theatre. Current IR techniques for Computer Assisted Orthopaedic Surgery (CAOS) are time consuming and costly. There is a need to automate and accelerate this process.

METHODS

Bespoke quick, cost effective, contactless and automated 3D laser scanning techniques based on the DAVID Laserscanner method were designed. 10 cadaveric knee joints were intra-operatively laser scanned and were registered with the pre-operative MRI scans. The results are supported with a concurrent validity study.

RESULTS

The average absolute errors between scan models were systematically less than 1 mm. Errors on femoral surfaces were higher than tibial surfaces (P<0.05). Additionally, scans acquired through the large exposure produced higher errors than the smaller exposure (P<0.05).

CONCLUSION

This study has provided proof of concept for a novel automated shape acquisition and registration technique for CAOS.

Multinuclear MR and multilevel data processing: an insight into morphologic assessment of in vivo knee articular cartilage

RATIONALE AND OBJECTIVES

Quantitative assessment of knee articular cartilage (AC) morphology using magnetic resonance (MR) imaging requires an accurate segmentation and 3D reconstruction. However, automatic AC segmentation and 3D reconstruction from hydrogen-based MR images alone is challenging because of inhomogeneous intensities, shape irregularity, and low contrast existing in the cartilage region. Thus, the objective of this research was to provide an insight into morphologic assessment of AC using multilevel data processing of multinuclear ((23)Na and (1)H) MR knee images.

MATERIALS AND METHODS

A dual-tuned ((23)Na and (1)H) radio-frequency coil with 1.5-T MR scanner is used to scan four human subjects using two separate MR pulse sequences for the respective sodium and proton imaging of the knee. Postprocessing is performed using customized routines written in MATLAB. MR data were fused to improve contrast of the cartilage region that is further used for automatic segmentation. Marching cubes algorithm is applied on the segmented AC slices for 3D volume rendering and volume is then calculated using the divergence theorem.

RESULTS

Fusion of multinuclear MR images results in an improved contrast (factor >3) in the cartilage region. Sensitivity (80.21%) and specificity (99.64%) analysis performed by comparing manually segmented AC shows a good performance of the automated AC segmentation. The average cartilage volume (23.19 ± 1.38 cm(3); coefficient of variation [COV] -0.059) measured from 3D AC models of four data sets shows a marked improvement over average cartilage volume (23.24 cm(3); COV -0.19) reported earlier.

CONCLUSIONS

This study confirms the use of multinuclear MR data for cartilage morphology (volume) assessment that can be used in clinical settings.

Acquisition and interactive 3D exploration of the internal structure of a dissected specimen

We present a system to keep track of a destructive process such as a medical specimen dissection, from data acquisition to interactive and immersive visualization, in order to build ground truth models. Acquisition is a two-step process, first involving a 3D laser scanner to get a 3D surface, and then a high resolution camera for capturing the texture. This acquisition process is repeated at each step of the dissection, depending on the expected accuracy and the specific objects to be studied. Thanks to fiducial markers, surfaces are registered on each others. Experts can then explore data using interaction hardware in an immersive 3D visualization. An interactive labeling tool is provided to the anatomist, in order to identify regions of interest on each acquired surface. 3D objects can then be reconstructed according to the selected surfaces. We aim to produce ground truths which for instance can be used to validate data acquired with MRI. The system is applied to the specific case of white fibers reconstruction in the human brain.

Laser surface estimation for microwave breast imaging systems

Microwave breast imaging techniques involve collecting measurements from a breast that is positioned in a scanner. While the patient interface typically includes a hole through which the breast is placed when the patient lies in the prone position, the exact location and shape of breast are not known. In this paper, we explore the addition of a laser sensor and associated algorithms in order to provide a rapid and accurate estimate of the breast surface location. We demonstrate that the laser is capable of estimating surfaces with improved accuracy compared to microwave measurements. The impact of accurate surface estimation on images is shown, and results obtained from human scans are presented.

Automatic morphometric cartilage quantification in the medial tibial plateau from MRI for osteoarthritis grading

OBJECTIVE

To evaluate whether a novel, fully automatic, morphometric cartilage quantification framework is suitable for assessing level of knee osteoarthritis (OA) in clinical trials.

METHOD

The population was designed with a normal population and groups with varying degree of OA of both sexes and at ages from 21 to 78. Posterior-anterior X-rays were acquired in semi-flexed, load-bearing position. The radiographic signs of OA were evaluated based on the Kellgren and Lawrence score (KL) and the joint space width (JSW) was measured. Turbo 3D T1 magnetic resonance imaging (MRI) scans were acquired with resolution 0.7x0.7x0.8mm(3) from a 0.18T scanner. The morphometric cartilage quantification from MRI resulted in volume, surface area, thickness and surface curvature for the medial tibial cartilage compartment. These quantifications were evaluated against JSW with respect to precision and ability to separate healthy subjects from OA subjects.

RESULTS

The automatic, morphometric cartilage quantifications allowed fairly precise measurements with scan-rescan coefficient of variations (CVs) in the range from 3.4% to 6.3%. All quantifications, including JSW, allowed separation of the groups of healthy and OA subjects. However, for separation of the healthy from the borderline cases (KL 0 vs KL 1), only the Cartilage Curvature quantification allowed statistically significant separation (P<0.01).

CONCLUSION

The novel morphometric framework shows promise for use in clinical trials. The ability of the Cartilage Curvature quantification to detect the early stages of OA and the effectiveness of the focal thickness Q10 measure are particularly noteworthy. Furthermore, these results may indirectly support that low-field MRI may be a low-cost option for clinical trials.