Reduction of Metal Artifact with Dual-Energy CT: Virtual Monospectral Imaging with Fast Kilovoltage Switching and Metal Artifact Reduction Software.

Imaging of patients with metal implants is a common activity for radiologists, and overcoming metal artifacts during computed tomography (CT) is still a challenge. Virtual monochromatic spectral (VMS) imaging with dual-energy CT has been reported to reduce beam-hardening metal artifact effectively. Dual-energy CT allows the synthesis of VMS images. Monochromatic images depict how the imaged object would look if the X-ray source produced X-ray photons at only a single-energy level. For this reason, VMS imaging improve image quality by reducing beam-hardening artifacts. Additional metal artifact reduction postprocessing such as metal artifact reduction software can be applied to improve the visualization of the bone-prosthesis interface, periprosthetic areas, and soft tissue near and far from the metal implant. This article summarizes how virtual monochromatic images are synthesized from dual-energy CT, and it describes and illustrates our clinical experience with a single-source dual-energy scanner with fast kilovoltage switching to reduce beam hardening in patients with metal implants.

Virtual monochromatic spectral imaging with fast kilovoltage switching: reduction of metal artifacts at CT.

With arthroplasty being increasingly used to relieve joint pain, imaging of patients with metal implants can represent a significant part of the clinical work load in the radiologist's daily practice. Computed tomography (CT) plays an important role in the postoperative evaluation of patients who are suspected of having metal prosthesis-related problems such as aseptic loosening, bone resorption or osteolysis, infection, dislocation, metal hardware failure, or periprosthetic bone fracture. Despite advances in detector technology and computer software, artifacts from metal implants can seriously degrade the quality of CT images, sometimes to the point of making them diagnostically unusable. Several factors may help reduce the number and severity of artifacts at multidetector CT, including decreasing the detector collimation and pitch, increasing the kilovolt peak and tube charge, and using appropriate reconstruction algorithms and section thickness. More recently, dual-energy CT has been proposed as a means of reducing beam-hardening artifacts. The use of dual-energy CT scanners allows the synthesis of virtual monochromatic spectral (VMS) images. Monochromatic images depict how the imaged object would look if the x-ray source produced x-ray photons at only a single energy level. For this reason, VMS imaging is expected to provide improved image quality by reducing beam-hardening artifacts.

Perirenal fluid collections and monoclonal gammopathy.

We report here a case with secondary polycythaemia, monoclonal gammopathy of undetermined significance and renal lymphangiectasis revealed by renal failure. Renal failure was probably linked to renal compression by fluid collections. Renal lymphangiectasis is a rare but has already been described in the literature. In addition, its association with a monoclonal paraprotein and polycythaemia seems to be a new clinical entity recently reported in only one patient.

Does load-bearing materials influence hip capsule thickness in total hip replacement? An MRI case-matched study.

BACKGROUND: Ceramic-on-ceramic (COC) total hip replacements (THR) have exhibited less instability and late dislocation. Hip capsule plays an important role in hip stability. Different surrounding soft tissue reactions have been observed according to the bearing material used but no study compared these data using MRI investigation. Therefore, we performed a retrospective case control study to compare hip capsule thicknesses according to the bearing materials in THR and in native hips. HYPOTHESIS: Hip capsule is thicker after COC THR compared to ceramic- or metal-on-polyethylene (PE) bearings, or native hips. MATERIALS AND METHOD: Magnetic resonance imaging (MRI) images, combined with a multi acquisition variable resonance image combination (MAVRIC) sequence, was used to measure the hip capsule thickness in 16 patients (29 hips) who had either COC (13 hips, median age at surgery: 64.8 years old, median follow-up at imaging: 2482 days), PE bearings (11 hips, median age at surgery: 48.4 years old (significantly different from COC THR), median follow-up at imaging: 1860 days (NS)), or a native hip with no implant (5 hips). Two independent radiologists measured capsular thicknesses in 4 different zones and were blinded regarding the bearing components. The imaged hips were classified into three groups: native, COC and PE. RESULTS: The COC THR group had the thickest capsules (median 7.0mm, range 2.9-15.5mm). This result was statistically significant (p<0.0001) when compared to PE THR (median 4.9mm, range 2.2-10.5mm), and to native hips (median 4.1mm, range 2.7-6.9mm) measurements, respectively. Furthermore, painful hips had thinner capsules (4.6mm, range 2-10.5) compared to not painful hips (6.8mm, range 2.3-15.5) (p=0.0006). DISCUSSION: This is the first in-vivo study measuring capsular thickness in THR with the objective of measuring variations according to the hip implant materials used. The results revealed a significantly thicker capsule for the COC bearing compared to either PE or native hips, and a thinner capsule in painful hips. LEVEL OF EVIDENCE: III, retrospective non-consecutive cohort study.

Tibial hyperostosis: a diagnostic approach.

Tibial hyperostosis may be encountered in musculoskeletal imaging, incidentally or during the investigation of a leg pain. Hyperostosis involves the exuberant production of osseous tissue and results in cortical, periosteal and/or endosteal thickening of the bone. As a long bone with thick cortices, the tibia has a significant probability of being affected by ubiquitous bone diseases. As a tubular long bone, the tibia is likely to be involved in extensive infectious conditions such as osteomyelitis. As a bone of the lower limb, the tibia undergoes high stresses and may be affected by decrease in bone strength or repetitive submaximal stress. The tibia is also particularly involved in some bone sclerosing dysplasias and Paget's disease. In this work, we aim at highlighting the main conditions leading to tibial hyperostosis and try to provide key elements to narrow down the several diagnostic possibilities. Osteoid osteomas, fatigue or insufficiency fractures, infectious conditions, vascular lesions, sclerosing bone dysplasias and Paget's disease represent the main challenging diagnoses to discuss.

An unusual cause of acute abdominal pain after cardiac surgery: acute epiploic appendagitis.

Abdominal complications following cardiac surgery remain unusual, but are associated with high mortality. The most common abdominal surgical complications are mesenteric ischaemia, diverticulitis, pancreatitis, gastrointestinal bleeding and cholecystitis. We describe a case of a 73-year old woman with acute abdominal pain mimicking cholecystitis on day 10 after aortic valve replacement. An abdominal examination showed tenderness of the right upper quadrant with Murphy's sign. Complete blood count, blood chemistries and urinalysis were normal as were the abdominal and chest X-rays and abdominal ultrasonography. The abdominal computed-tomography (CT) scan enabled us to rule out cholecystitis, as it demonstrated the typical appearance of epiploic appendagitis on the right colon, 1 cm below the gallbladder. Epiploic appendagitis results from twisting, kinking or venous thrombosis of an epiploic appendage. Depending on its localization, it mimics many diagnoses requiring surgery: colitis, diverticulitis, appendicitis and cholecystitis. An abdominal CT scan is the diagnostic imaging tool of choice. All physicians involved in post-cardiac surgery care should be aware of this self-limiting disease that usually resolves with non-steroidal anti-inflammatory drugs and watchful waiting, and to avoid unnecessary surgery because the spontaneous evolution of epiploic appendagitis is usually benign.