title: Use of ultrasound-magnetic resonance image fusion to guide sacroiliac joint injections: a preliminary assessment.
abstract: BACKGROUND
  The sacroiliac joint is one of the sources of chronic lower back pain. Intra-articular injections of anesthetic drugs and/or steroids are currently used in these cases for diagnostic and therapeutic purposes. However, given the anatomic and functional complexity of the joint, imaging guidance is mandatory during such procedures. In this context, the technique of fusing images obtained with two different modalities can often overcome the limitations and enhance the advantages of single-modality guidance.
  
  
  OBJECTIVE
  The aim of this study was to evaluate the technique of ultrasound (US)-magnetic resonance (MR) image fusion to guide intra-articular injections of drugs into the sacroiliac joint.
  
  
  METHODS
  We evaluated seven sacroiliac joints in six patients with sacroiliac pain syndrome (four females, two males; mean age 59 years; range 46-76 years). Five were candidates for radiofrequency thermolysis, and a therapeutic nerve block was performed in the sixth. Using the volume navigation system, we fused three-dimensional MR images with simultaneously acquired real-time ultrasound images and used them to guide the intra-articular injections.
  
  
  RESULTS
  In all patients, spatial accuracy was considered excellent, with definition of registration errors of less than 3 mm. The diagnostic blocks produced positive results in all patients with 80 % reductions in pain (measured with a Numerical Rating Scale, NRS) relative to baseline. The patient who underwent the therapeutic nerve block experienced complete resolution of symptoms that has been maintained over time. There were no complications.
  
  
  CONCLUSIONS
  US-MR imaging fusion guidance of sacroiliac joint injections is feasible and effective, in accordance with the data in the literature. The use of the MR for three-dimensional imaging eliminates the risk of radiation exposure.
authors.affiliation: IRCCS Foundation, San Matteo Medical Center, Institute of Radiology, University of Pavia, Pavia, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Zacchino
authors.affiliation: IRCCS Foundation, San Matteo Medical Center, Institute of Radiology, University of Pavia, Pavia, Italy.
authors.forename: J
authors.initials: J
authors.lastname: Almolla
authors.affiliation: IRCCS Foundation, San Matteo Medical Center, Institute of Radiology, University of Pavia, Pavia, Italy.
authors.forename: E
authors.initials: E
authors.lastname: Canepari
authors.affiliation: IRCCS Foundation, San Matteo Medical Center, Institute of Radiology, University of Pavia, Pavia, Italy.
authors.forename: V
authors.initials: V
authors.lastname: Merico
authors.affiliation: IRCCS Foundation, San Matteo Medical Center, Institute of Radiology, University of Pavia, Pavia, Italy.
authors.forename: F
authors.initials: F
authors.lastname: Calliada
keywords: Image fusion technique; Sacroiliac joints; Ultrasound