Technical Innovation
Musculoskeletal Imaging
June 2009

Functional Joint Imaging Using 256-MDCT: Technical Feasibility

Abstract

OBJECTIVE. Musculoskeletal functional imaging should encompass the real-time (dynamic) depiction of joints in motion (kinematic). Our goal was to determine the technical feasibility of performing dynamic–kinematic imaging of the knee and wrist joints using a new technique, 256-MDCT.
CONCLUSION. Dynamic–kinematic imaging of the wrist and knee using 256-MDCT is feasible to depict anatomic and functional information, warranting further study of diagnostic efficacy, and could augment the current repertoire of joint dysfunction diagnostic testing.

Introduction

Medical imaging is a critical component in the diagnosis of joint dysfunction, and, in the past, radiology has focused predominantly on the static, morphologic depiction of joint internal derangements. Because motion is an integral function of the musculoskeletal system, evaluating joint dysfunction could be enhanced by a robust method for functional imaging because the basis for some of these disorders has only been inferred. Kinematic imaging, as extended from classical mechanical physics, is concerned with describing the motions of objects. Dynamic imaging refers to the ability to acquire real-time imaging data. Functional imaging from a musculoskeletal perspective encompasses the real-time (dynamic) depiction of joints in motion (kinematic) under physiologic conditions and hence the proposed designation of dynamic–kinematic imaging.
The ideal characteristics for functional musculoskeletal imaging are image acquisition with suitable field of view, spatial resolution, contrast resolution, and temporal resolution under physiologic conditions with 4D rendering and quantitative processing. Several imaging techniques have been applied for functional imaging, and each has limitations with respect to the ideal characteristics (Table 1).
TABLE 1: Comparison of Imaging Techniques for Functional Joint Imaging
TechniqueAdvantagesLimitations
FluoroscopyDynamic image acquisition (sufficient temporal resolution), volumetric imaging, high spatial resolutionProjectional technique with overlapping structures obscuring relationships of interest
SonographyDynamic image acquisition (sufficient temporal resolution), imaging during physiologic activityLimited contrast resolution with respect to osseous structures, limited field of view with respect to entire-joint imaging
MRIVery good contrast resolution for soft-tissue structuresInsufficient temporal resolution to capture joint motion during single acquisition, lesser spatial resolution, bore size prohibiting physiologic motion
MDCT
High spatial resolution; suitable contrast resolution between bone, ligament, tendon, and muscle; volumetric imaging; dynamic image acquisition (sufficient temporal resolution)
Limited field of view with respect to entire-joint imaging (64-MDCT does not allow greater than 32-mm coverage in the z direction during a single acquisition)
With the development of 256-MDCT, many of the limitations of other imaging techniques and of 64-MDCT imaging are overcome (Table 2), facilitating 4D analysis with volumetric acquisition of an entire joint in motion without the need to translate the gantry (no table motion, only joint motion) [1]. Our goal was to determine the technical feasibility of dynamic–kinematic imaging of the knee and wrist joints using 256-MDCT.
TABLE 2: Comparison of Dynamic 64-MDCT Versus 256-MDCT
Parameter64-MDCT256-MDCT
Coverage (mm) in z direction of patient32128
Slice width (mm)0.50.5
Approximate radiation exposure (100-mm scan range)1.7 mSv (170 mrem)0.5 mSv (50 mrem)
Temporal resolution (musculoskeletal protocols)0.5 s per rotation (500 ms)0.5 s per rotation (500 ms)
New imaging capabilitiesCoronary artery imaging (shorter breath-holds), intercerebral aneurysms, clips, and coilsDynamic examinations of large organs such as heart and liver
Other advantagesIncreased patient tolerance of examination; 350-μm isotropic imagingAbility to perform dynamic and perfusion studies; shorter scan time; reduced radiation exposure to patient; higher spatial resolution; fast temporal resolution; superior low-contrast resolution; more time points captured, yielding more natural joint movement
Shortcomings
Detector size not large enough for many whole-organ imaging protocols (e.g., heart) in a single rotation
Requires high-quality reconstruction algorithms due to increased cone angle

Materials and Methods

This HIPAA-compliant study was approved by our institutional review board and funded by Toshiba Medical Systems with an unrestricted grant. Because this was a feasibility study, the sample size was small to show technical capacity. After informed consent was obtained, six adult nonpregnant volunteer subjects were enrolled for 256-MDCT of the knee and wrist, with three subjects allocated to bilateral knee imaging for patellofemoral evaluation (n = 6 knees) and three subjects allocated to bilateral wrist imaging for supination–pronation (n = 6 wrists) and radioulnar deviation (n = 6 wrists). The six participants were screened and had no history of joint pathology or surgery in the examined joints. The average age of the group was 43.5 years (age range, 34–61 years).
All examinations were performed using a prototype FDA-approved 256-MDCT scanner (Aquilon 256, Toshiba Medical Systems). The x-ray detector is composed of 256 × 0.5 mm detectors delivering 12.8 cm of coverage in the z-axis. A single rotation of the detector takes 0.5 second. A detailed description of this device is available elsewhere [2]. The primary investigator coached and then observed the participants performing the joint motion of interest before imaging. Participants also practiced and showed the proper joint motion in the CT gantry without imaging to verify comprehension and compliance and to avoid unnecessary repeat imaging. Gonadal shielding was applied to all subjects.
Unenhanced CT images were acquired by a trained technologist during a complete cycle of joint motion without any apparatus. Three subjects performed knee extension from a 90° flexed starting position, with each knee examined separately. Three subjects were placed in the prone position, with wrists above the head, and performed wrist abduction from a fully-adducted position for radioulnar deviation evaluation, and the same three subjects performed full wrist pronation from a supinated position. Image acquisition time was 10 seconds for each volume. Two-dimensional multiplanar reformations, 3D surface-shaded (bone) and volume-rendered (bone and soft tissue), and 4D cine loop images were reconstructed from the source data. Image processing was performed using Vitrea software (Vital Images).
Fig. 1A 38-year-old man with healthy knee. Volume CT images obtained during knee flexion using 256-MDCT scanner show good image quality of 2D axial section with soft-tissue window through mid patellofemoral articulation (A), 2D midline sagittal section with bone window (B), and 3D volume-rendered image accentuating patellar tendon (C). Minimal artifact is present at cephalad and caudal aspects of B due to incomplete rotation and missing data for reconstruction (truncation artifact), which is amplified on volume-rendered image (C). See also Figures S1D and S1E, cine loops, viewed from information box in upper right corner of this article.
Fig. 1B 38-year-old man with healthy knee. Volume CT images obtained during knee flexion using 256-MDCT scanner show good image quality of 2D axial section with soft-tissue window through mid patellofemoral articulation (A), 2D midline sagittal section with bone window (B), and 3D volume-rendered image accentuating patellar tendon (C). Minimal artifact is present at cephalad and caudal aspects of B due to incomplete rotation and missing data for reconstruction (truncation artifact), which is amplified on volume-rendered image (C). See also Figures S1D and S1E, cine loops, viewed from information box in upper right corner of this article.
Fig. 1C 38-year-old man with healthy knee. Volume CT images obtained during knee flexion using 256-MDCT scanner show good image quality of 2D axial section with soft-tissue window through mid patellofemoral articulation (A), 2D midline sagittal section with bone window (B), and 3D volume-rendered image accentuating patellar tendon (C). Minimal artifact is present at cephalad and caudal aspects of B due to incomplete rotation and missing data for reconstruction (truncation artifact), which is amplified on volume-rendered image (C). See also Figures S1D and S1E, cine loops, viewed from information box in upper right corner of this article.
Two musculoskeletal radiologists experienced in CT performed the subjective analysis of image quality in consensus using the Vitrea viewer on a diagnostic-quality workstation. Each joint was evaluated separately for a total of 18 evaluations (six knees, flexion–extension; six wrists, supination–pronation; and six wrists, radioulnar deviation). The observers evaluated the 2D and 3D images for diagnostic quality (poor, fair, good, or excellent). Quality definitions were as follows: poor was defined as noninterpretable and nondiagnostic; fair was defined as limited by artifact, signal to noise, or spatial or contrast resolution yet possibly interpretable; good was defined as diagnostic with minimal artifact; and excellent was defined as diagnostic without artifact and similar or superior to current 64-MDCT images. The observers evaluated the ability to depict joint motion (well depicted, adequately depicted, or poorly depicted) on the 4D dynamic–kinematic images. Definitions were as follows: poorly depicted was defined as nondiagnostic, unable to view smooth joint motion or determine the bone relationships; adequately depicted was defined as able to view joint motion and determine bone relationships but limited by artifact or nonsmooth movement; and well depicted was defined as able to view smooth continuous joint motion and identify the bone relationships without artifact.

Results

Knee and wrist image quality for 2D and 3D images was rated as good for all 18 evaluations, with some artifacts noted at the extreme edges secondary to incomplete data for reconstruction (truncation artifact). The ability to depict normal joint relationships for wrist and knee motion was rated as well depicted for all 18 evaluations. No device malfunctions or complications occurred. Knee images of one subject are shown in Figure 1A, 1B, 1C. Cine images (Fig. S1D; viewed from the information box in the upper right corner of this article) showed normal translation of the patella from multiple angles and the extensor mechanism tendons throughout knee flexion (Fig. S1E; viewed from the information box in the upper right corner of this article). Wrist images of one subject performing radioulnar deviation are shown in Figure 2A, 2B, 2C, 2D. Cine images showed normal fluidlike movement of the carpus at multiple angles (Fig. S2E; viewed from the information box in the upper right corner of this article) and positions of associated soft tissues throughout the range of motion (Fig. S2F; viewed from the information box in the upper right corner of this article). Wrist images of one subject performing supination and pronation are shown in Figure 3A, 3B, 3C, 3D. Cine images showed normal rotation of the radius with respect to the ulna (Fig. S3E; viewed from the information box in the upper right corner of this article) and positions of associated soft tissues throughout the range of motion (Fig. S3F; viewed from the information box in the upper right corner of this article). The alignment of the carpus and the distal radioulnar joint was well depicted and qualitatively showed normal motion without an instability pattern in these healthy subjects.

Discussion

In this pilot investigation, we found that 256-MDCT dynamic–kinematic imaging adequately depicted, by subjective visualization, real-time unconstrained joint motion of the knee and wrist bilaterally from a single acquisition. We chose the knee joint because patellofemoral maltracking is a common disorder. We chose the wrist because it is a complex joint with multiple small articulations and degrees of freedom with subtle ranges of motion. Compared with 64-MDCT, 256-MDCT offers numerous advantages (Table 2).
Our use of 256-MDCT eliminated the image quality degradation experienced by one study seen in the mid motion phase of wrist radioulnar deviation using retrospectively gated 64-MDCT [3]. The ability to render any axis of joint motion from different perspectives may allow a more comprehensive evaluation of pathomechanics. Patellofemoral maltracking relates to many disorders and, although some cases are readily defined, the pathomechanics may be difficult to observe. Accurate measurement of patellofemoral tracking (normal and abnormal) has not been achieved yet in experimental or clinical conditions. Such information would be valuable in the diagnosis and treatment of patellofemoral disorders [4].
The common clinical problem of carpal instability is often difficult to diagnose with sufficient accuracy to direct specific appropriate treatment. To improve this situation, an imaging method that could elucidate the mechanical and kinematic complexity inherent in the anatomic design of the carpus would be useful [5]. This would allow more appropriate classification and thus treatment of carpal instabilities, such as perilunate instabilities, midcarpal instabilities, or proximal carpal instabilities. This may be especially useful for carpal instability nondis sociative variety. Chronic distal radioulnar joint (DRUJ) instability can be due to an osseous deformity, a ligamentous injury, or a combination of both.
Fig. 2A 41-year-old man with healthy wrist. Volume CT images acquired during radioulnar deviation using 256-MDCT scanner show good image quality of 2D axial section through proximal carpal row (A), 2D coronal section through carpus (B), 3D surface-shaded image of wrist bones bilaterally (C), and 3D volume-rendered image accentuating tendons and muscles (D). See also Figures S2E and S2F, cine loops, viewed from information box in upper right corner of this article.
Fig. 2B 41-year-old man with healthy wrist. Volume CT images acquired during radioulnar deviation using 256-MDCT scanner show good image quality of 2D axial section through proximal carpal row (A), 2D coronal section through carpus (B), 3D surface-shaded image of wrist bones bilaterally (C), and 3D volume-rendered image accentuating tendons and muscles (D). See also Figures S2E and S2F, cine loops, viewed from information box in upper right corner of this article.
Fig. 2C 41-year-old man with healthy wrist. Volume CT images acquired during radioulnar deviation using 256-MDCT scanner show good image quality of 2D axial section through proximal carpal row (A), 2D coronal section through carpus (B), 3D surface-shaded image of wrist bones bilaterally (C), and 3D volume-rendered image accentuating tendons and muscles (D). See also Figures S2E and S2F, cine loops, viewed from information box in upper right corner of this article.
Fig. 2D 41-year-old man with healthy wrist. Volume CT images acquired during radioulnar deviation using 256-MDCT scanner show good image quality of 2D axial section through proximal carpal row (A), 2D coronal section through carpus (B), 3D surface-shaded image of wrist bones bilaterally (C), and 3D volume-rendered image accentuating tendons and muscles (D). See also Figures S2E and S2F, cine loops, viewed from information box in upper right corner of this article.
Typically, current imaging evaluation is performed with bilateral axial CT in supination, pronation, and neutral static positions; however, the DRUJ could be better visualized for joint congruence anomalies, transient subluxations, and deficiencies in the soft-tissue stabilizers using dynamic–kinematic imaging. With 256-MDCT, examination of entire joints and joint ranges of motion—such as the shoulder; elbow; carpometacarpal joints; hip; ankle; and, as in our study, knee and wrist—will be possible within the confines of the gantry. Examination of localized spine segments (up to 12.8 cm) and temporomandibular joints will also be possible with reduced motion artifact.
Possible limitations of 256-MDCT include radiation dose exposure, which is less an issue for extremity imaging because the gonads and other radiosensitive organs are not exposed. The radiation doses for CT reported in the literature vary, mostly because of technical differences between scanner generations (e.g., 16-MDCT vs 64-MDCT) and between the scanners from various manufacturers [6]. To examine an extremity joint with a 64-MDCT scanner, one could obtain multiple helical scans, moving the joint slightly between each acquisition. If this were to be done for a 100-mm scan range over nine positions, the effective dose for a 64-MDCT scanner would be about 1.7 mSv (170 mrem). For a similar acquisition on the prototype 256-MDCT system, the effective dose would be 0.5 mSv (50 mrem) [7]. On the basis of this information, direct dose calculations were not obtained as part of our research study protocol. Another limitation was the lack of load bearing during imaging. One important distinction in functional imaging is load-bearing or stress imaging of a joint. This involves application of a force, physiologic or simulated, to reveal pathoanatomy not present at rest in the context of positional or load-induced pain and does not necessitate dynamic imaging. However, true functional joint imaging would encompass physiologic loads or imaging during symptomatic conditions (movements and loads). We will need to determine the suitability of this approach for each clinical application and introduce, as needed, a load-bearing component to recapitulate physiologic conditions. Truncation artifact limits evaluation at each end of the volume acquisition in the z direction. With the advent of 320-MDCT, the acquisition field of view is expanded to 16 cm allowing for complete interpolation over a larger z dimension than 256-MDCT. This extension would allocate a useable field of view of about 14 cm by discarding the incompletely reconstructed portions of the image at the fringe, eliminating the truncation artifact we saw.
Fig. 3A 55-year-old man with healthy wrist. Volume CT images acquired during supination–pronation movement using 256-MDCT scanner show good image quality of 2D axial section with bone tissue window through distal radioulnar joint (DRUJ) (A), 2D coronal section with bone tissue window through mid DRUJ (B), 3D surface-shaded image in semisupinated position (C), and 3D volume-rendered image showing tendons and muscles (D). See also Figures S3E and S3F, cine loops, viewed from information box in upper right corner of this article.
Fig. 3B 55-year-old man with healthy wrist. Volume CT images acquired during supination–pronation movement using 256-MDCT scanner show good image quality of 2D axial section with bone tissue window through distal radioulnar joint (DRUJ) (A), 2D coronal section with bone tissue window through mid DRUJ (B), 3D surface-shaded image in semisupinated position (C), and 3D volume-rendered image showing tendons and muscles (D). See also Figures S3E and S3F, cine loops, viewed from information box in upper right corner of this article.
Fig. 3C 55-year-old man with healthy wrist. Volume CT images acquired during supination–pronation movement using 256-MDCT scanner show good image quality of 2D axial section with bone tissue window through distal radioulnar joint (DRUJ) (A), 2D coronal section with bone tissue window through mid DRUJ (B), 3D surface-shaded image in semisupinated position (C), and 3D volume-rendered image showing tendons and muscles (D). See also Figures S3E and S3F, cine loops, viewed from information box in upper right corner of this article.
Fig. 3D 55-year-old man with healthy wrist. Volume CT images acquired during supination–pronation movement using 256-MDCT scanner show good image quality of 2D axial section with bone tissue window through distal radioulnar joint (DRUJ) (A), 2D coronal section with bone tissue window through mid DRUJ (B), 3D surface-shaded image in semisupinated position (C), and 3D volume-rendered image showing tendons and muscles (D). See also Figures S3E and S3F, cine loops, viewed from information box in upper right corner of this article.
In conclusion, 256-MDCT dynamic–kinematic imaging is feasible for evaluating patients with knee and wrist disorders and represents the next development in functional imaging of joint disorders. Future avenues of investigation will encompass obtaining objective information with quantitative analyses of osseous, articular, and soft-tissue structures to provide more insight into clinical signs and symptoms and to measure treatment effects after surgery or rehabilitation.

Acknowledgments

We thank Amber Jones, Johns Hopkins Interventional Neuroradiology Division, for organizing the research study; Antonio Machado, Johns Hopkins Radiology, for assistance with image processing; Richard T. Mather, Toshiba Medical Systems, for radiation dose calculation; and Chloe Steveson, Toshiba Medical Systems, for technical references and review of 256-MDCT.

Footnotes

Supported by an unrestricted grant from Toshiba Medical Systems.
Address correspondence to J. A. Carrino ([email protected]).
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Supplemental Content

File (vid_1_knee_ext_to_flexion_bony_anatomy.avi)
File (vid_2_knee_ext_to_flexion_soft_tissue.avi)
File (vid_3_wrist_dorsum_bony_anatomy.avi)
File (vid_4_wrist_dorsum_soft_tissue.avi)
File (vid_5_wrist_supination_2d_axial_bony_anatomy.wmv)
File (vid_6_wrist_supination_soft_tissue.avi)

References

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Mori S, Endo M, Obata T, et al. Clinical potentials of the prototype 256-detector row CT-scanner. Acad Radiol 2005; 12:148 –154
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Mori S, Endo M, Tsunoo T, et al. Physical performance evaluation of a 256-slice CT-scanner for four-dimensional imaging. Med Phys 2004; 31:1348 –1356
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Tay SC, Primak A, Fletcher J, et al. Four-dimensional computed tomographic imaging in the wrist: proof of feasibility in a cadaveric model. Skeletal Radiol 2007; 36:1163 –1169
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Katchburian MV, Bull AM, Shih YF, et al. Measurement of patellar tracking: assessment and analysis of the literature. Clin Orthop Relat Res 2003; 412:241 –259
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Miller RJ. Wrist MRI and carpal instability: what the surgeon needs to know and the case for dynamic imaging. Semin Musculoskelet Radiol 2001; 5:235 –240
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Mori S, Endo M, Nishizawa K, et al. Comparison of patient doses in 256-slice CT and 16-slice CT scanners. Br J Radiol 2006; 79:56 –61
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Mori S, Nishizawa K, Ohno M, et al. Conversion factor for CT dosimetry to assess patient dose using a 256-slice CT scanner. Br J Radiol 2006; 79:888 –892

Information & Authors

Information

Published In

American Journal of Roentgenology
Pages: W295 - W299
PubMed: 19457792

History

Submitted: September 8, 2008
Accepted: October 27, 2008

Keywords

  1. 256-MDCT
  2. carpal instability
  3. distal radioulnar joint
  4. dynamic CT
  5. knee
  6. tracking disorder
  7. wrist

Authors

Affiliations

Vivek Kalia
Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD.
Rick W. Obray
Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD.
Ross Filice
Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD.
Laura M. Fayad
Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD.
Kieran Murphy
Department of Medical Imaging, University of Toronto, Toronto, ON, Canada.
John A. Carrino
Section of Musculoskeletal Radiology, Russell H. Morgan Department of Radiology and Radiological Science and Department of Orthopaedic Surgery, Johns Hopkins University School of Medicine, 601 N Caroline St., JHOC 5165, Baltimore, MD 21287.

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