Three-dimensional movements of the lumbar spine facet joints and segmental movements: in vivo examinations of normal subjects with a new non-invasive method.

INTRODUCTION: Examination with CT and image registration is a new technique that we have previously used to assess 3D segmental motions in the lumbar spine in a phantom. Current multi-slice computed tomography (CT) offers highly accurate spatial volume resolution without significant distortion and modern CT scanners makes it possible to reduce the radiation dose to the patients. Our aim was to assess segmental movement in the lumbar spine with the aforementioned method in healthy subjects and also to determine rotation accuracy on phantom vertebrae. MATERIAL AND METHOD: The subjects were examined in flexion-extension using low dose CT. Eleven healthy, asymptomatic subjects participated in the current study. The subjects were placed on a custom made jig which could provoke the lumbar spine into flexion or extension. CT examination in flexion and extension was performed. The image analysis was performed using a 3D volume fusion tool, registering one of the vertebrae, and then measuring Euler angles and distances in the registered volumes. RESULTS: The mean 3D facet joint translation at L4-L5 was in the right facet joint 6.1 mm (3.1-8.3), left facet joint 6.9 mm (4.9-9.9), at L5-S1: right facet joint 4.5 mm (1.4-6.9), and for the left facet joint 4.8 mm (2.0-7.7). In subjects the mean angles at the L4-L5 level were: in the sagittal plane 14.3°, coronal plane 0.9° (-0.6 to 2.8), and in the transverse plane 0.6° (-0.4 to 1.5), in the L5-S1 level the rotation was in sagittal plane 10.2° (2.4-16.1), coronal plane 0° (-1.2 to 1.2), and in the transverse plane 0.2° (-0.7 to 0.3). Repeated analysis for 3D facet joint movement was on average 5 mm with a standard error of mean of 0.6 mm and repeatability of 1.8 mm (CI 95%). For segmental rotation in the sagittal plane the mean rotation was 11.5° and standard error of mean 1°. The repeatability for rotation was 2.8° (CI 95%). The accuracy for rotation in the phantom was in the sagittal plane 0.7°, coronal plane 1°, and 0.7 in the transverse plane. CONCLUSION: This method to assess movement in the lumbar spine is a truly 3D method with a high precision giving both visual and numerical output. We believe that this method for measuring spine movement is useful both in research and in clinical settings.

A new technique for measuring wear in total hip arthroplasty using computed tomography.

Accurately estimating polyethylene wear in 3 dimensions, without the need for additional procedures or equipment, is of significant interest. We investigated the use of a high-resolution clinical computed tomographic (CT) scanner to estimate femoral head displacement relative to the cup as an indirect method of estimating polyethylene wear. A hip phantom was used to simulate the 3-dimensional displacement of a femoral head. The phantom was imaged in a high-resolution CT scanner. The mean difference between the true phantom displacement as positioned by micrometers and the calculated displacement based on the CT images was as follows: for the x-axis, 0 mm (SD, 0.213; SE, 0.058); y-axis, 0.039 mm (SD, 0.035; SE, 0.026); and z-axis, 0.039 mm (SD, 0.051; SE, 0.020).

Model studies on segmental movement in lumbar spine using a semi-automated program for volume fusion.

OBJECTIVE: To validate a new non-invasive CT method for measuring segmental translations in lumbar spine in a phantom using plastic vertebrae with tantalum markers and human vertebrae. MATERIAL AND METHODS: One hundred and four CT volumes were acquired of a phantom incorporating three lumbar vertebrae. Lumbar segmental translation was simulated by altering the position of one vertebra in all three cardinal axes between acquisitions. The CT volumes were combined into 64 case pairs, simulating lumbar segmental movement of up to 3 mm between acquisitions. The relative movement between the vertebrae was evaluated visually and numerically using a volume fusion image post-processing tool. Results were correlated to direct measurements of the phantom. RESULTS: On visual inspection, translation of at least 1 mm or more could be safely detected and correlated with separation between the vertebrae in three dimensions. There were no significant differences between plastic and human vertebrae. Numerically, the accuracy limit for all the CT measurements of the 3D segmental translations was 0.56 mm (median: 0.12; range: -0.76 to +0.49 mm). The accuracy for the sagittal axis was 0.45 mm (median: 0.10; range: -0.46 to +0.62 mm); the accuracy for the coronal axis was 0.46 mm (median: 0.09; range: -0.66 to +0.69 mm); and the accuracy for the axial axis was 0.45 mm (median: 0.05; range: -0.72 to + 0.62 mm). The repeatability, calculated over 10 cases, was 0.35 mm (median: 0.16; range: -0.26 to +0.30 mm). CONCLUSION: The accuracy of this non-invasive method is better than that of current routine methods for detecting segmental movements. The method allows both visual and numerical evaluation of such movements. Further studies are needed to validate this method in patients.

Fusion of radiostereometric analysis data into computed tomography space: application to the elbow joint.

Improvement of joint prostheses is dependent upon information concerning the biomechanical properties of the joint. Radiostereometric analysis (RSA) and electromagnetic techniques have been applied in previous cadaver and in vivo studies on the elbow joint to provide valuable information concerning joint motion axes. However, such information is limited to mathematically calculated positions of the axes according to an orthogonal coordinate system and is difficult to relate to individual skeletal anatomy. The aim of this study was to evaluate the in vivo application of a new fusion method to provide three-dimensional (3D) visualization of flexion axes according to bony landmarks. In vivo RSA data of the elbow joint's flexion axes was combined with data obtained by 3D computed tomography (CT). Results were obtained from five healthy subjects after one was excluded due to an instable RSA marker. The median error between imported and transformed RSA marker coordinates and those obtained in the CT volume was 0.22 mm. Median maximal rotation error after transformation of the rigid RSA body to the CT volume was 0.003 degrees . Points of interception with a plane calculated in the RSA orthogonal coordinate system were imported into the CT volume, facilitating the 3D visualization of the flexion axes. This study demonstrates a successful fusion of RSA and CT data, without significant loss of RSA accuracy. The method could be used for relating individual motion axes to a 3D representation of relevant joint anatomy, thus providing important information for clinical applications such as the development of joint prostheses.

A new computed tomography-based radiographic method to detect early loosening of total wrist implants.

BACKGROUND: Diagnosis of loosening of total wrist implants is usually late using routine radiographs. Switching modality to computed tomography (CT) should aid in early diagnosis. PURPOSE: To propose and evaluate the accuracy of a new CT method for assessing loosening of the carpal component in total wrist arthroplasty. MATERIAL AND METHODS: A protocol encompassing volume registration of paired CT scans of patients with unexplained pain in a prosthetically replaced wrist (used in clinical routine) is presented. Scans are acquired as a dynamic examination under torsional load. Using volume registration, the carpal component of the prosthesis is brought into spatial alignment. After registration, prosthetic loosening is diagnosed by a shift in position of the bones relative to the prosthesis. This study is a preclinical validation of this method using a human cadaverous arm with a cemented total wrist implant and tantalum markers. Seven CT scans of the arm were acquired. The scans were combined into 21 pairs of CT volumes. The carpal component was registered in each scan pair, and the residual mismatch of the surrounding tantalum markers and bone was analyzed both visually and numerically. RESULTS: The detection limit for prosthetic movement was less than 1 mm. CONCLUSION: The results of this study demonstrate that CT volume registration holds promise to improve detection of movement of the carpal component at an earlier stage than is obtainable with plain radiography.

Image formats: five years after the AAPM standard for digital image interchange.

The publication of AAPM Report No. 10 was the first attempt to standardize image formats in the medical imaging community. Since then, three other groups have formed (CART--the Scandinavian collaboration for Computer Assisted Radiation Therapy treatment planning; ACR-NEMA, a collaboration whose purpose is to formulate a standard digital interface to medical imaging equipment; and COST B2 Nuclear Medicine Project a European collaboration whose purpose is to define a format for digital image exchange in Nuclear Medicine). The AAPM format uses key-value pairs in plain text to keep track of all information associated with a particular image. The radiation oncology community in the U.S. has been defining key-value pairs for use with CT, nuclear medicine and magnetic resonance (MR) images. The COST B2 Nuclear Medicine Project has also adopted this format and together with the Australian/New Zealand Society of Nuclear Medicine Technical Standards Sub-Committee which has also adopted this format, has defined an initial set of key-value pairs for Nuclear Medicine images. Additionally, both ACR-NEMA and CART have been defining fields for use with the same types of images. The CART collaboration has introduced a database which is available electronically, but is maintained by a group of individuals. ACR-NEMA operates through committee meetings. The COST B2 Nuclear Medicine Project operates through electronic (and postal where necessary) mail. To insure a consistent set of field names in such a rapidly developing arena requires the use of a server rather than a committee. Via a server a person would inquire if a particular field had been defined. If so, the defined name would be returned.(ABSTRACT TRUNCATED AT 250 WORDS)

QSH: a minimal but highly portable image display and handling toolkit.

We describe a software system developed to handle images obtained from different sources, namely, computer-assisted tomography, positron emission tomography, single photon emission tomography and magnetic resonance imaging. In developing the system, it was necessary to address the following points. (1) The types of values that were encountered in both the header information and the pixel elements, namely, integers, floating point numbers, complex numbers and strings. (2) The use of domain-dependent sets of keys, that is, how to choose keys and how to stabilize the use of keys among the user population. This is, for example, how information such as the patient name, or the activity in becquerel is kept. It is necessary to keep both the key values and the units. (3) The development of a method for providing a database using flat files, i.e. linear text. (4) The maintenance of a history of values and operations. This is necessary in order to address the problem of determining from an image how that image was produced. The connection between an image and how it was derived is analogous to describing how a secondary standard is derived from a primary one.

Computed tomography analysis of radiostereometric data to determine flexion axes after total joint replacement: application to the elbow joint.

Kinematic analysis for in vivo assessment of elbow endoprostheses requires knowledge of the exact positions of motion axes relative to bony landmarks or the prosthesis. A prosthesis-based reference system is required for comparison between individuals and studies. The primary aim of this study was to further develop an earlier described algorithm for fusion of radiostereometric analysis (RSA) data and data obtained in 3D computed tomography (CT) for application to the elbow after total joint replacement. The secondary aim was to propose a method for marking of prostheses in 3D CT, enabling definition of a prosthesis-based reference system. Six patients with elbow endoprostheses were investigated. The fusion of data made it possible to visualize the motion axes in relation to the prostheses in the 3D CT volume. The differences between two repeated positioning repetitions of the longitudinal prosthesis axis were less than 0.6 degrees in the frontal and sagittal planes. Corresponding values for the transverse axis were less than 0.6 degrees in the frontal and less than 1.4 degrees (in four out of six less than 0.6 degrees ) in the horizontal plane. This study shows that by fusion of CT and RSA data it is possible to determine the accurate position of the flexion axes of the elbow joint after total joint replacement in vivo. The proposed method for implant marking and registration of reference axes enables comparison of prosthesis function between patients and studies.

A potential means of improving the evaluation of deformity corrections with Taylor spatial frames over time by using volumetric imaging: preliminary results.

OBJECTIVE: In this study we explore the possibility of accurately and cost-effectively monitoring tibial deformation induced by Taylor Spatial Frames (TSFs), using time-separated computed tomography (CT) scans and a volume fusion technique to determine tibial rotation and translation. MATERIALS AND METHODS: Serial CT examinations (designated CT-A and CT-B, separated by a time interval of several months) of two patients were investigated using a previously described and validated volume fusion technique, in which user-defined landmarks drive the 3D registration of the two CT volumes. Both patients had undergone dual osteotomies to correct for tibial length and rotational deformity. For each registration, 10 or more landmarks were selected, and the quality of the fused volume was assessed both quantitatively and via 2D and 3D visualization tools. First, the proximal frame segment and tibia in CT-A and CT-B were brought into alignment (registered) by selecting landmarks on the frame and/or tibia. In the resulting "fused" volume, the proximal frame segment and tibia from CT-A and CT-B were aligned, while the distal frame segment and tibia from CT-A and CT-B were likely not aligned as a result of tibial deformation or frame adjustment having occurred between the CT scans. Using the proximal fused volume, the distal frame segment and tibia were then registered by selecting landmarks on the frame and/or tibia. The difference between the centroids of the final distal landmarks was used to evaluate the lengthening of the tibia, and the Euler angles from the registration were used to evaluate the rotation. RESULTS: Both the frame and bone could be effectively registered (based on visual interpretation). Movement between the proximal frame and proximal bone could be visualized in both cases. The spatial effect on the tibia could be both visually assessed and measured: 34 mm, 10 degrees in one case; 5 mm, 1 degrees in the other. CONCLUSION: This retrospective analysis of spatial correction of the tibia using Taylor Spatial Frames shows that CT offers an interesting potential means of quantitatively monitoring the patient's treatment. Compared with traditional techniques, modern CT scans in conjunction with image processing provide a high-resolution, spatially correct, and three-dimensional measurement system which can be used to quickly and easily assess the patient's treatment at low cost to the patient and hospital.

Assessing wear of the acetabular cup using computed tomography: an ex vivo study.

PURPOSE: To validate a clinically useful method for measuring acetabular cup wear using computed tomography (CT). MATERIAL AND METHODS: Eight uncemented acetabular cups were scanned twice ex vivo using CT. The linear penetration depth of the femoral component head into the cup and the thickness of the remaining polyethylene liner were measured in the CT volumes using dedicated software. Two independent examiners twice assessed each volume. The CT measurements were compared to direct measurements using a coordinate measuring device and micrometer measurements. RESULTS: Accuracy of wear measurements expressed as penetration depth was +/-0.6 and +/- 1.0 mm for the two examiners, respectively, with no significant differences between examiners, trials, and CT scans. Accuracy of measurements of remaining polyethylene was +/- 1.3 and +/- 1.0 mm, respectively, for the two examiners. Systematic differences between examiners were found, but no significant differences between trials and CT scans. These differences were due to different interpretations of metal artifacts in the volumes. CONCLUSION: The proposed CT method for evaluating wear as head penetration depth allows for reliable wear detection at a clinically relevant level. Measurements of remaining polyethylene on CT volumes are not as reliable as wear measurements owing to metal artifacts.

Standard orientation of the pelvis: validation on a model and ten patients.

PURPOSE: To validate an image post-processing method for re-orienting the pelvis in CT volumes to a standardized orientation in a model and in 10 patients. MATERIAL AND METHODS: Twenty-four CT volumes of a pelvic model and 10 pairs of postoperative total hip arthroplasty (THA) patient CT scans were rotated to a defined pelvic standard orientation and the rotation was recorded. For precision, a test-retest procedure was used. For accuracy, three exactly represented coordinate points were used. For clinical application, the standard orientation was used for calculating the direction of acetabular cup migration from a previous model study. RESULTS: Precision of pelvic standard orientation, calculated as maximal directional error, was better than 1 degrees in the model study and better than 1.5 degrees in the patient study. Accuracy, expressed as angle between ideal and measured coordinate axes, was 0.1 degrees for x, y, z axes. No measurable systematic errors were found. When applied to acetabular cup migration in the model, standardization of pelvic orientation had no significant effect on the measurements. CONCLUSION: Reorienting the pelvis during image post-processing was shown to be accurate. It enables measurements relative to the pelvis and minimizes the dependency of patient positioning.

Standardizing the raster display for medical images using a fixed set of frame buffer primitives.

Two major difficulties associated with medical image processing are the diverse image formats that must be dealt with because of the differences in image sources and the number of incompatible display systems available for viewing images both before and after processing. We describe a very small set of primitives that need to be defined to utilize any raster display. When these primitives have been implemented for a particular device, then a standard set of image display programs can be compiled and images and the results of image processing can be displayed. The main purpose of this paper is to describe what a raster display looks like from the point of view of the programmer and to define the specific hardware and software data about the raster display that must be known in order to implement the small set of primitives.

Multimodality image display: desirable frame buffer characteristics.

The intent of this paper is to understand the characteristics of those frame buffers currently used to display images, versus more ideal frame buffers for medical image display purposes. This study is based on current needs and what characteristics might be desirable. Two case examples are presented: (1) a system developed for high quality computer graphics and (2) a system developed for nuclear medicine and radiation therapy treatment planning. Our study considers: (1) defining a pixel depth sufficient to hold data, (2) the desirability of multiple color look-up tables, (3) how cine loops are managed, and (4) display memory size.

A modular computer system for the nuclear medicine/ultrasound laboratory.

Computer-controlled graphic displays are a necessity in many nuclear medicine studies. The authors propose using a set-up consisting of three modules: (a) a display system based on television technology; (b) an instrument interface employing list mode and having a low information loss rate; and (c) flexible modular software which can easily be tailored to the needs of both radiologists and technicians. The authors consider a mini-computer system with broad, flexible applications to be a valuable tool, particularly for those function studies which can only be done by means of nuclear medicine techniques.

A modular computer system for the nuclear medicine/ultrasound laboratory: a multidisciplinary proposal.

In many nuclear Medicine studies computer-controlled graphic displays are an absolute necessity for obtaining meaningful results. Design criteria developed by an interdisciplinary scientific panel are presented to achieve a display system based on television technology; an instrument interface employing list mode using bubble-memory storage technology, thus having a low information-loss rate; and flexible modular software easily tailored to the specific needs of both clinicians and technicians. The panel considers a minicomputer system with broad, flexible applications to be a valuable tool, particularly in doing those function studies that only can be done via nuclear medicine techniques. The final specifications ultimately allow the selection of a vendor and hospital installation, even though all criteria are not currently achievable.

Local area networks in an imaging environment.

There is great interest at present in incorporating image-management systems popularly referred to as picture archiving and communication systems (PACS) into imaging departments. This paper will describe various aspects of local area networks (LANs) for medical images and will give a definition of terms and classification of devices by describing a possible system which links various digital image sources through a high-speed data link and a common image format, allows for viewing and processing of all images produced within the complex, and eliminates the transport of films. The status of standards governing LAN and particularly PACS systems along with a proposed image exchange format will be given. Prototype systems, particularly a system for nuclear medicine images, will be presented, as well as the prospects for the immediate future in terms of installations started and commercial products available. A survey of the many questions that arise in the development of a PACS for medical images and also a survey of the presently suggested/adopted answers will be given.

Use of graphical techniques for error evaluation.

Anatomic localization in functional (such as PET) imaging often requires a structural (such as CT or NMRI) study of the brain in the same plane. Some neuropsychiatric conditions make it difficult for a patient to hold his/her head immobile even when a rigid head holder is used. We studied the effect of tilt of the anatomic reference image, in this instance CT, relative to the functional image, here PET, on the quantification of receptor ligand concentration in anatomically defined regions of the brain.

Graphical 3D medical image registration and quantification.

We present a graphical three-dimensional method that facilitates image registration and fusion, and provides quantitative geometric and volume information. In particular it enhances the use of functional (radiopharmaceutical) imaging (SPECT, PET) which, though a powerful clinical tool, has the disadvantage of low spatial resolution and ill-defined boundaries. Registration between functional images and structural images (MRI, CT) can augment the anatomical context of these functional images.