CTArthrography, MR Arthrography, PET, and Scintigraphy in Osteoarthritis Patrick Omoumi, MDa,b, GustavoA. Mercier, MD, PhDc, Frederic Lecouvet, MD, PhDa, Paolo Simoni, MDa, Bruno C.Vande Berg, MD, PhDa,* KEYWORDS CT arthrography MR arthrography PET PET-CT Scintigraphy Osteoarthritis Cartilage Damage to articular cartilage is considered to be no radiopharmaceuticals to image the articular the hallmark of osteoarthritis (OA), even if other cartilage in clinical practice. factors are involved in the pathogenesis of the We review technical aspects of CT arthrography disease. The radiological assessment of OA has and MR arthrography of various joints, compare been based mostly on the radiographic grading both methods, and report on their most common of the joint space width, an indicator of cartilage and useful indications, as well as their pitfalls and thickness, and on indirect signs such as osteo- limitations. We also describe in detail the nuclear phytes.1–3 Attempts have been made to better medicine methods that might be relevant for OA delineate cartilage lesions by using intraarticular research and clinical application. contrast material in arthrography,4 which has inherent limitations due to the projection of three- dimensional structures on a plane. The advent of CT ARTHROGRAPHYAND MR ARTHROGRAPHY cross-sectional imaging enabled arthrography to Technical Considerations 5–7 develop further. Indeed, arthrographic tech- Type of contrast material with CT arthrography niques such as computed tomography (CT) CT arthrography can be performed using either arthrography and magnetic resonance (MR) a single (iodine) or double-contrast (iodine and arthrography, thanks to their high resolution and air) technique. In the past, air was used with the possibility of multiplanar imaging, remain conventional arthrography to distend the joints, superior to conventional MR imaging for the delin- which is not necessary when using CT, because eation of surface lesions of all cartilage areas. the penetration of the air into cartilage lesions is However, MR imaging is the only technique poor when compared with that of fluid. Nowadays, enabling the analysis of the internal structure of there is a general consensus in using a single- cartilage, and many recent developments include contrast technique, which is easier to perform8,9 2 biochemical qualitative assessment. and probably less painful.10 The development of nuclear medicine tech- Dilution of the contrast material can be achieved niques have focused mainly on the subchondral with local anesthetics or saline to avoid beam- changes associated with OA, because there are hardening artifacts. Nevertheless, the dilution a Department of Radiology, Cliniques Universitaires Saint-Luc, Universite´ Catholique de Louvain, Brussels, Belgium b Department of Radiology, Centre Hospitalo-Universitaire de Tours, Tours, France c Department of Radiology, Nuclear Medicine and Molecular Imaging, Boston University Center, Boston, MA, USA * Corresponding author. E-mail address: [email protected] (B.C. Vande Berg). Radiol Clin N Am 47 (2009) 595–615 doi:10.1016/j.rcl.2009.04.005 0033-8389/09/$ – see front matter ª 2009 Published by Elsevier Inc. radiologic.theclinics.com 596 Omoumi et al mainly depends on the radiologist preference and surface landmarks.36–38 The choice relies on the investigated joint.11–17 radiologist’s preference and on the equipment available. The injection technique follows standard Type of contrast material with MR arthrographic procedures, which have been widely arthrography described in the literature.39–41 The contrast material of choice for MR arthrogra- phy is gadolinium-based (gadolinium-DTPA). It is Time delay between the injection of contrast possible to perform either indirect (less invasive, material and imaging intravenous gadolinium-DTPA injection) or direct Once injected in the joint, the concentration of MR arthrography (intraarticular gadolinium injec- contrast materials rapidly decreases by diffusion tion). For the study of cartilage, the intraarticular into the cartilage and synovium, resorption, and injection of contrast material is favored because fluid influx into the joint.42 It is recommended to it allows joint repletion, thus, better delineation of perform the CT within 30 minutes and the MR 18 superficial cartilage defects. Other types of within an hour after the contrast injection.23,29,43,44 contrast material have also been tested, such as The time delay, however, varies according to the saline combined with T2-weighted MR imaging, joint. The use of epinephrine in adjunction to the but gadolinium provides the best contrast-to- injected material (for instance by mixing 1 mL of 19–21 noise ratios. A metaanalysis of 112 published a 0.1% solution containing 1 mg of epinephrine studies found gadolinium-DTPA to be a safe and with 10 mL of contrast material45) slows down efficient technique for diagnosing internal the resorption of the latter.46,47 However, the use 22 derangement of joints. of epinephrine may increase postarthrographic Many studies have focused on determining the morbidity.10 Use of epinephrine is usually not best gadolinium-DTPA concentration and necessary with MR arthrography.48 temporal behavior of intraarticular contrast after It has been shown for the shoulder that exercise injection. At 1.5 T, a concentration of 2–2.5 has no beneficial or detrimental effect for MR mmol/L is considered best for imaging to be per- arthrography.49 However, in our experience, active 22,23 formed within about an hour after injection. and passive full-range articular motion after the 24 At 3.0 T, a slightly greater dilution may be useful. injection allows the contrast material to completely Aspiration of joint effusion before injection can cover cartilage surfaces.50 prevent excessive dilution of contrast material, but this is usually not a problem in clinical Acquisition parameters 24,25 practice. CT arthrography exposes the patient to ionizing It has been shown that iodinated and gadoli- radiation. Radiation doses should be kept to nium-based contrast material can safely be mixed, a minimum, especially in regions close to sensi- and combined MR arthrography and CT arthrogra- tive areas such as the shoulder (Fig. 2) (thyroid) phy examinations have successfully been and the hip (gonads), at the expense of signal- obtained for comparison of both studies to-noise ratio. The minimal field-of-view should 26–29 (Fig. 1). However, at 3.0 T, the presence of be selected. In knee CT arthrography, for iodinated contrast agents has to be minimized, instance, the suprapatellar recess should not be because signal-to-noise peak levels are lower at imaged (Fig. 3). Synovial and intraarticular 24 3.0 T than at 1.5 T. pathologies are depicted on conventional radio- Volume of contrast material graphs obtained early after intraarticular injection, The volume of injected contrast material neces- before imbibition occurs and masks synovial sary for proper capsular distention varies accord- masses. These radiographs in the case of the ing to the joint and is the same for all knee will cover the suprapatellar recess not arthrographic techniques. As a rule, adequate imaged by CT. distention is indicated by increased resistance to The CT acquisition parameters include narrow injection or retrograde flow of contrast material collimation, low-pitch values, and a high milliam- into the needle after disconnection of the pere–second value to obtain high resolution 51 syringe.30 The injection should be stopped if the isotropic multiplanar reformats. The reconstruc- patient has pain. tions use bone algorithms, providing high spatial resolution images, and bone windowing is used Injection technique to view the images. Posttreatment of these high- The injection is usually performed under fluoro- resolution isotropic images may include curved scopic guidance,16,30 but other injection tech- and maximum-intensity projection reformatting niques have been described, using CT,16,31 (Fig. 4). Metallic artifacts can be diminished and, ultrasound,32–34 MR 35 guidance, or even by using more generally, signal-to-noise ratio can be CT and MR Arthrography, PET, and Scintigraphy in OA 597 Fig.1. 34-year-old man with history of trauma. Combined CT arthrography and MR arthrography were obtained after intraarticular injection of gadolinium and iodine. Normal aspect of cartilage (white arrowheads) and partial tear of central portion of scapholunate ligament (arrow). (A) Coronal fat-suppressed spin-echo T1-weighted MR arthrography image (669/11 ms, TR/TE) shows normal wrist cartilage with intermediate signal intensity (arrow- head). Its surface is smooth and regular. (B) 2.4 mm-thick coronal CT arthrography reformatted image shows normal hypodense cartilage, well delimited by the underlying subchondral bone and the intraarticular contrast material at its surface. (C) A 0.6 mm thick coronal CT arthrography reformatted image obtained from same exam- ination demonstrates the same findings. Retrospectively increasing the reformat thickness [from (C)to(B)] leads to an increase of the signal-to-noise ratio. Note that the thickness of the cartilage is easier to evaluate at CT arthrography than at MR arthrography, with better coverage of cartilage surface areas by the contrast material at CT arthrography (open arrowheads). increased by retrospectively increasing the thick- patients who have metallic hardware near the joint ness of the reformats and, at the expense of (Fig. 5).8,54 spatial resolution, by using soft