Brian P. Jacob, David C. Chen, Bruce Ramshaw, Shirin Towfigh (eds.) - The SAGES Manual of Groin Pain-Springer International Publishing (2016)

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Fig. 13.7. Axial CT of the pelvis demonstrates bony erosions of the bilateral
iliac wings ( black arrows ) with sparing of the sacrum ( white arrows ), consistent
with sacroiliitis. Ferguson view of the pelvis (“pelvic outlet radiograph” not
shown) will accentuate the sacroiliac joints and may reveal sacroiliitis without
the need for CT.
Fig. 13.8. Axial, sagittal, and coronal CT reveal loop of bowel ( asterisks ) exiting
the peritoneal cavity below the inguinal ligament and medial to the femoral
vessels ( black arrows ), diagnostic of femoral hernia.
Magnetic Resonance
Magnetic resonance scanners utilize low-energy light to interact with
the hydrogen atoms found throughout most organic tissues. The electromagnet
inside an MR scanner is always “on,” and typically operating at
1.5 T of field strength (roughly 10,000 times the strength of the Earth’s
natural field) although 3 T scanners are becoming more widely available
in routine clinical imaging. This magnetic field provides energy to
hydrogen atoms, forcing them to line up along the direction of the magnet
much in the way that a compass needle will line up with the Earth.
Once the hydrogen atoms line up, the machine can communicate with
them by sending out radio-frequency pulses that only specific atoms are
able to respond to, forcing them to change direction and oppose the