Multichannel CT Imaging of Orthopedic Hardware and Implants

Abstract

The introduction of multichannel CT scanners provides both radiologists and surgeons with a new tool to image patients with orthopedic hardware. The key parameters that have made it possible to image the implants and the surrounding bone with multichannel CT are the higher available technical factors (kVp and mAs) coupled with the ability to acquire thin slices over a large scan region. These properties make it possible to produce high-quality multiplanar reformations that facilitate visualization of the orthopedic device and the surrounding bone. An important consideration for multichannel CT imaging of hardware is the reduction of cone beam artifacts caused by the geometry of multichannel CT scanners. This artifact is reduced by using a narrower x-ray beam collimation and a low pitch setting. This article discusses CT scan parameters and image postprocessing used at our institution and illustrates common clinical problems encountered when imaging implanted orthopedic devices. These include fracture healing, loosening of joint prostheses, evaluation of particle disease, and the use of CT for preoperative planning in revision arthroplasty.

Imaging of Postoperative Avascular Necrosis of the Ankle and Foot

“…The use of fast spin-echo and short tau inversion recovery sequences reduces metal-related artifacts compared with gradient-echo and frequency-selective fat saturation sequences. 13,14 We have observed an increase in susceptibility and misregistration artifacts increase with greater field strength (1.5 T to 3.0 T), although broader receiver bandwidth and the higher gradient field strengths used partially offsets the effect. Imaging parameter optimization at higher field strength may include using a small field of view, increasing the resolution (matrix size), use of thin slices, increasing the echo train length, and increasing the bandwidth.…”

“…Image distortion at the bone/hardware interface ("splay artifact") previously seen with the imaging of large joint prostheses is less pronounced with the greater number of detector rows and lower pitch settings of modern machines. 13 Use of smooth reconstruction filters and slices slightly thicker than the minimum slice thickness available on the scanner also reduces splay artifact and image noise. 13,14 Modern scanners suppress streak artifacts caused by metal implants without increasing dose by applying inbuilt reconstruction techniques to smooth areas with deficient photon counts in the raw data.…”

“…13 Use of smooth reconstruction filters and slices slightly thicker than the minimum slice thickness available on the scanner also reduces splay artifact and image noise. 13,14 Modern scanners suppress streak artifacts caused by metal implants without increasing dose by applying inbuilt reconstruction techniques to smooth areas with deficient photon counts in the raw data. In the small joints of the ankle and foot where minimal hardware is usually present, artifacts are usually less pronounced (►Fig.…”

A review of the clinical approach to persistent pain following total hip replacement

“…24,25 Accurate measurement of the acetabulum cup version can be achieved with CT because of the ability to measure in multiple orthogonal planes. [26][27][28][29] Other potential uses of CT include preoperative assessment of bone loss for acetabulum and femur, evaluation of bone density for stress shielding, and detection of osteolysis, liner wear, and metallosis.…”

Image quality of cone beam computed tomography for evaluation of extremity fractures in the presence of metal hardware: visual grading characteristics analysis

“…20,21 The performance of dedicated CBCT scanners for the evaluation of fracture healing in the extremities needs to be assessed in the presence of metal hardware, 15 as the cone-beam geometry and the typically reduced X-ray tube output along with lower mean X-ray beam energy of the CBCT scanners may affect the appearance and severity of the artefacts. 19,22,23 In this study, our objective was to evaluate the image quality and interobserver reliability of a novel dedicated extremity CBCT scanner when compared with radiography, for the assessment of fracture healing in the presence of metal hardware.…”