Reduction of coil mass artifacts in high-resolution flat detector conebeam CT of cerebral stent-assisted coiling.

BACKGROUND AND PURPOSE: Developments in flat panel angiographic C-arm systems have enabled visualization of both the neurovascular stents and host arteries in great detail, providing complementary spatial information in addition to conventional DSA. However, the visibility of these structures may be impeded by artifacts generated by adjacent radio-attenuating objects. We report on the use of a metal artifact reduction algorithm for high-resolution contrast-enhanced conebeam CT for follow-up imaging of stent-assisted coil embolization. MATERIALS AND METHODS: Contrast-enhanced conebeam CT data were acquired in 25 patients who underwent stent-assisted coiling. Reconstructions were generated with and without metal artifact reduction and were reviewed by 3 experienced neuroradiologists by use of a 3-point scale. RESULTS: With metal artifact reduction, the observers agreed that the visibility had improved by at least 1 point on the scoring scale in >40% of the cases (κ = 0.6) and that the streak artifact was not obscuring surrounding structures in 64% of all cases (κ = 0.6). Metal artifact reduction improved the image quality, which allowed for visibility sufficient for evaluation in 65% of the cases, and was preferred over no metal artifact reduction in 92% (κ = 0.9). Significantly higher scores were given with metal artifact reduction (P < .0001). CONCLUSIONS: Although metal artifact reduction is not capable of fully removing artifacts caused by implants with high x-ray absorption, we have shown that the image quality of contrast-enhanced conebeam CT data are improved drastically. The impact of the artifacts on the visibility varied between cases, and yet the overall visibility of the contrast-enhanced conebeam CT with metal artifact reduction improved in most the cases.

Computer-assisted planning and navigation for corrective distal radius osteotomy, based on pre- and intraoperative imaging.

Malunion after a distal radius fracture is very common and if symptomatic, is treated with a so-called corrective osteotomy. In a traditional distal radius osteotomy, the radius is cut at the fracture site and a wedge is inserted in the osteotomy gap to correct the distal radius pose. The standard procedure uses two orthogonal radiographs to estimate the two inclination angles and the dimensions of the wedge to be inserted into the osteotomy gap. However, optimal correction in 3-Dspace requires restoring three angles and three displacements. This paper introduces a new technique that uses preoperative planning based on 3-D images. Intraoperative 3-D imaging is also used after inserting pins with marker tools in the proximal and distal part of the radius and before the osteotomy. Positioning tools are developed to correct the distal radius pose in six degrees of freedom by navigating the pins. The method is accurate ( d 1.2 mm, ϕ 0.9°, m TRE = 1.7 mm), highly reproducible (SE (d) < 1.0 mm, SE (ϕ) ≤ 1.4°, SE (m) (TRE) = 0.7 mm), and allows intraoperative evaluation of the end result. Small incisions for pin placement and for the osteotomy render the method minimally invasive.

The effect of tendon loading on in-vitro carpal kinematics of the wrist joint.

Measurements of in-vitro carpal kinematics of the wrist provide valuable biomechanical data. Tendon loading is often applied during cadaver experiments to simulate natural stabilizing joint compression in the wrist joint. The purpose of this study was to investigate the effect of tendon loading on carpal kinematics in-vitro. A cyclic movement was imposed on 7 cadaveric forearms while the carpal kinematics were acquired by a 4-dimensional rotational X-ray imaging system. The extensor- and flexor tendons were loaded with constant force springs of 50 N, respectively. The measurements were repeated without a load on the tendons. The effect of loading on the kinematics was tested statistically by using a linear mixed model. During flexion and extension, the proximal carpal bones were more extended with tendon loading. The lunate was on the average 2.0 degrees (p=0.012) more extended. With tendon loading the distal carpal bones were more ulnary deviated at each angle of wrist motion. The capitate was on the average 2.4 degrees (p=0.004) more ulnary deviated. During radioulnar deviation, the proximal carpal bones were more radially deviated with the lunate 0.7 degrees more into radial deviation with tendon loading (p<0.001). Conversely, the bones of distal row were more flexed and supinated with the capitate 1.5 degrees more into flexion (p=0.025) and 1.0 degrees more into supination (p=0.011). In conclusion, the application of a constant load onto the flexor and extensor tendons in cadaver experiments has a small but statistically significant effect on the carpal kinematics during flexion-extension and radioulnar deviation.

In-vivo three-dimensional carpal bone kinematics during flexion-extension and radio-ulnar deviation of the wrist: Dynamic motion versus step-wise static wrist positions.

An in-vivo approach to the measurement of three-dimensional motion patterns of carpal bones in the wrist may have future diagnostic applications, particularly for ligament injuries of the wrist. Static methods to measure carpal kinematics in-vivo only provide an approximation of the true kinematics of the carpal bones. This study is aimed at finding the difference between dynamically and statically acquired carpal kinematics. For eight healthy subjects, static and a dynamic measurements of the carpal kinematics were performed for a flexion-extension and a radio-ulnar deviation movement. Dynamic scans were acquired by using a four-dimensional X-ray imaging system during an imposed cyclic motion. To assess static kinematics of the wrists, three-dimensional rotational X-ray scans were acquired during step-wise flexion-extension and radio-ulnar deviation. The helical axis rotations and the rotation components. i.e. flexion-extension, radio-ulnar deviation and pro-supination were the primary parameters. Linear mixed model statistical analysis was used to determine the significance of the difference between the dynamically and statically acquired rotations of the carpal bones. Small and in most cases negligible differences were observed between the dynamic motion and the step-wise static motion of the carpal bones. The conclusion is that in the case of individuals without any pathology of the wrist, carpal kinematics can be studied either dynamically or statically. Further research is required to investigate the dynamic in-vivo carpal kinematics in patients with dynamic wrist problems.

Does intraoperative fluoroscopic 3D imaging provide extra information for fracture surgery?

Fracture surgery of the extremities using 2D fluoroscopy frequently fails to detect the suboptimal positioning of implants and joint incongruities. The use of intraoperative 3D-rotational X-ray (3D-RX) imaging with a new X-ray device potentially reveals these failures. We compared 50 intraoperative (2D) results of surgery and certainty about the effectiveness of different aspects of fracture reduction as interpreted from conventional (2D) methods versus intraoperative 3D-RX in 42 distal extremity fractures by means of a surgery questionnaire. In addition, we investigated the need for revision surgery based on postoperative radiological findings in 81 patients. After fracture reduction, just before a 3D-RX scan, the surgeon preoperatively assessed the result of surgery. Three months after surgery, the 3D-RX scan was judged by three experienced surgeons independently. Intraoperative 3D-RX showed significantly more information as to screw positioning and rotation of the fracture reduction than the conventional method (p < 0.005). None of the 81 patients in whom 3D-RX was performed needed surgical revision based on postoperative radiological examinations. Intraoperative 3D-RX with this new device scanning offers additional information about extremity fracture reduction as compared to conventional intraoperative 2D imaging, and may reduce the need for revision surgery. The value of 3D-RX on functional outcomes still needs to be assessed.

Cochlear implant electrode array insertion monitoring with intra-operative 3D rotational X-ray.

During cochlear implantation surgery, we use a mobile C-arm with 3D functionality to acquire per-operative 3D X-ray images. Scanning the multielectrode array is performed once before removal of the stylet and once after full insertion. When dissatisfied with the position of the multielectrode a repositioning is considered which happened occasionally. The major advantage is the extra certainty of the multielectrode array position in the cochlea with low-dose and little extra time. All cochlear implantations are now routinely scanned during surgery.