Diagnostic Tools and Imaging Methods in Intervertebral Disk Degeneration Sharmila Majumdar, PhD a,b, *, Thomas M. Link, MD a , Lynne S. Steinbach, MD a , Serena Hu, MD b , John Kurhanewicz, PhD a The incidence of back pain is ubiquitous in many societies; it has been reported as ranging from 8% to 80%. 1–3 Most people experiencing back pain have self-limited episodes; however, a small proportion of this pain becomes chronic and de- bilitating (see the article by Karppinen and colleagues elsewhere in this issue for further exploration of this topic). Disorders of the low back have may compromise quality of life and present a tremendous financial impact on society through lost productivity, increased health care, and societal costs. 4,5 In contrast to individuals with spinal degeneration resulting in spinal stenosis and disk herniation, those with disk degeneration have much more variable presenta- tions and responses to treatment. Although aging of individuals inevitably leads to aging and degen- eration of the spine, it has been proposed that physiologic degeneration is a different clinical entity from pathologic degeneration, with the implication that chronic back pain is the exception rather than the rule and that those with pathologic degeneration do not have appropriate repair or compensatory mechanisms (see the article by Chan and colleagues elsewhere in this issue for further exploration of this topic). Intervertebral disks provide stable support to adjacent vertebral bodies and allow movement to the vertebral bodies, thereby affecting spinal flex- ibility. They absorb and distribute loads during daily activities. Intervertebral disks undergo age- related degeneration, increase in back pain, and stiffness. The connections between pain and disk degeneration are not fully understood (see the arti- cles by Inoue and Espinoza Orias, and Karppinen and colleagues, elsewhere in this issue for further exploration of this topic). The intervertebral disk is composed of the nucleus pulposus, the annulus fibrosus, and the cartilaginous end-plates (see the article by Grun- hagen and colleagues elsewhere in this issue for further exploration of this topic). The nucleus pulposus is a viscous, mucoprotein gel that is approximately centrally located within the disk 6 and is composed of glycosaminoglycans in a loose network of type II collagen. The annulus fibrosus forms the outer boundary of the disk and is made up of type-I collagen fibers arranged in lamellae. The proteoglycans of the nucleus osmot- ically exert a “swelling pressure” that enables it to support spinal compressive loads. The pressur- ized nucleus also creates tensile stress within the a Department of Radiology and Biomedical Imaging, University of California San Francisco, Campus Box 2520, QB3 Building, 2nd Floor, Suite 203, 1700 4th Street, San Francisco, CA 94158, USA b Department of Orthopedic Surgery, University of California San Francisco, 1500 Owens Street, San Francisco, CA 94158, USA * Corresponding author. Department of Radiology and Biomedical Imaging, University of California San Francisco, Campus Box 2520, QB3 Building, 2nd Floor, Suite 203, 1700 4th Street, San Francisco, CA 94158. E-mail address: Sharmila.Majumdar@ucsf.edu KEYWORDS  Spine  Imaging  Disk  Magnetic resonance  Spectroscopy  T 1rho  T 2 Orthop Clin N Am 42 (2011) 501–511 doi:10.1016/j.ocl.2011.07.007 0030-5898/11/$ – see front matter Ó 2011 Elsevier Inc. All rights reserved. orthopedic.theclinics.com