Sports Medicine: Just the Facts

CHAPTER 43 • MAGNETIC RESONANCE IMAGING: TECHNICAL CONSIDERATIONS AND UPPER EXTREMITY 257

pain in collegiate athletes: a prospective study. Am J Phys Med
Rehabil80(8):572–7, 2001.
Nadler SF, Malanga GA, Bartoli LA, et al: Hip muscle imbalance
and low back pain in athletes: influence of core strengthening.
Med Sci Sports Exerc34(1):9–16, 2002a.
Nadler SF, Malanga GA, Feinberg JH, et al: Functional perform-
ance deficits in athletes with previous lower extremity injury.
Clin J Sport Med12(2):73–78, 2002b.
Nadler SF, Moley P, Malanga GA, et al: Functional deficits in
athletes with a history of low back pain: a pilot study. Arch
Phys Med Rehabil83(12):1753–8, 2002c.
Nadler SF, Steiner DJ, Petty SR, et al: Continuous low-level
heatwrap for treating acute nonspecific low back pain. Arch
Phys Med Rehabil84(3):329–334, 2003.
NCAA: Injury Surveillance System (1997–1998). Overland Park,
KS, National Collegiate Athletic Association, 1998.
Nyska M, Constantini N, Cale-Benzoor M, et al: Spondylolysis
as a cause of low back pain in swimmers. Int J Sports Med
21(5):375–379, 2000.
Pollock, ML, Leggett, SH, Graves JE, et al: Effect of resistance
training on lumbar extension strength. Am J Sports Med
17:624–629, 1989.
Rachbauer F, Sterzinger W, Eibl G: Radiographic abnormalities
in the thoracolumbar spine of young elite skiers. Am J Sports
Med29(4):446–449, 2001.
Sinaki M, Mokri B: Low back pain and disorders of the lumbar
spine, in Braddom RL (ed.): Physical Medicine and
Rehabilitation,2nd ed. Philadelphia, PA, Saunders, 2000,
pp 853–893.
Spencer CW, 3rd, Jackson DW: Back injuries in the athlete. Clin
Sports Med2(1):191–215, 1983.
Stanish W: Low back pain in athletes: An overuse syndrome. Clin
Sports Med6(2):321–344, 1987.
Sward L, Hellstrom M, Jacobsson B, et al: Disc degeneration and
associated abnormalities of the spine in elite gymnasts. A mag-
netic resonance imaging study. Spine16(4):437–443, 1991.

43 MAGNETIC RESONANCE

IMAGING: TECHNICAL

CONSIDERATIONS AND UPPER

EXTREMITY

Carolyn M Sofka, MD

TECHNICAL CONSIDERATIONS

• Nuclei with an inherent magnetic dipole moment (i.e.,
  odd number of protons or neutrons) are suitable for
  magnetic resonance (MR) imaging (Hendrick, 1994).
  In clinical medical imaging, most often, this is hydro-
  gen (H+).
  
  
  • When an external magnetic field (B 0 ) is applied to
    living tissues the hydrogen nuclei align either with or
    against the external magnetic field, producing a local
    magnetization force (Hendrick, 1994).
  
  
  • Precession (ω 0 ) is the continuous change in the direc-
    tion of this regional tissue magnetization and is deter-
    mined by both the strength of the external magnetic
    field, B 0 , as well as the gyromagnetic ratio of the
    nucleus (H+) being used in the MR experiment, γ, (the
    Larmor frequency) ω 0 = γB 0 (Hendrick, 1994).
  
  
  • Longitudinal magnetization is the amount of tissue
    magnetization in the direction of the main magnetic
    field B 0 (Hendrick, 1994).
    •T 1 (relaxation time) is the time required for longitudi-
    nal magnetization to recover 63% of its value before a
    second 90° radiofrequency (RF) pulse is applied
    (Hendrick, 1994).
    •T 2 is the time for transverse magnetization to decay
    37% of its original value. Both the inevitable effects
    of dephasing as well as the strength of the external
    magnetic field determine T 2 (Hendrick, 1994).
    •A basic spin echo pulse sequence resulting from
    applying a 90°RF pulse, waiting a certain time inter-
    val (TE/2), applying an additional 180°RF pulse, and
    then measuring the signal (spin echo) (Hendrick,
    1994). Repetition time(TR) is the time between 90°
    pulses and Echo time(TE) is the time from 90°pulse
    to the center of the spin echo (Hendrick, 1994).
    •Tissues with short T 1 values (e.g., fat) are bright on a
    T 1 -weighted sequence and those with long T 1 times
    (water) are dark on T 1 -weighted images. A T 1 -
    weighted image has a short TR and a short TE.
  
  
  • The TR value of a sequence determines the ultimate
    T 1 -weighting of an image and the TE determines the
    amount of T 2 -weighting (Plewes, 1994).
  
  
  • In fast spin echo sequencing, raw data is collected
    simultaneously using multiple 180°refocusing pulses,
    resulting in multiple spin echoes being acquired
    during one sequence (Plewes, 1994). This results in an
    overall shortened imaging time.
  
  
  • Other MR pulse sequences such as gradient echo
    imaging, fat suppression or inversion recovery tech-
    niques, and contrast-enhanced imaging are often per-
    formed in musculoskeletal imaging.
    •Fat suppression and inversion recovery sequences are
    water-sensitive pulse sequences; these are used to
    evaluate for bone marrow edema, intramuscular
    edema, joint effusions, and tendon sheath effusions.
  
  
  • Contrast-enhanced imaging uses a T 1 -shortening agent
    (gadolinium), injected either intravenously or intra-
    articularly. As gadolinium is a T 1 -shortening agent,
    areas of enhancement will be bright on T 1 -weighted
    sequences; the conspicuity of contrast-enhancement is
    increased if fat suppression technique is used in addition