Cath Lab Digest

   Magnetic resonance imaging has become a prominent imaging modality in diagnosing osteomyelitis in the foot and ankle. Studies report diagnostic sensitivities of MRI for osteomyelitis in the lower extremity as high as 90 to 95 percent.¹⁹ A MRI allows early detection of bone, bone marrow and soft tissue abnormalities with a higher specificity than other advanced imaging modalities.¹⁹ Primary MRI findings for osteomyelitis include bone marrow signal abnormalities representing a decreased T1 signal and increased T2 signal.²² Secondary MRI findings involve adjacent soft tissue defects, cellulitis, sinus tracts or cortical bone erosion.²⁰

   However, advances in the evaluation of the MRI of the foot and ankle are still occurring. Collins and colleagues recently established that T1 weighted imaging that demonstrates a decreased marrow signal is superior in diagnosing osteomyelitis in comparison to T2 weighted imaging abnormalities.¹⁹

   Limitations of MRI do exist aside from the well-documented contraindications (i.e. pacemaker/automated implantable cardioverter defribrillator). Gadolinium contrast enhanced MRI is not suitable for patients with peripheral vascular disease or chronic kidney disease, comorbidities commonly occurring in those with diabetes.²¹ Gout, arthritis, trauma and neuropathic osteoarthropathy can also mimic bone marrow signal abnormalities as those abnormalities are indistinguishable from those of osteomyelitis. Therefore, these conditions can drastically diminish the effectiveness and diagnostic capabilities of MRI in assessing osteomyelitis.²²

Exploring The Diagnostic Efficacy Of Nuclear Medicine

Nuclear medicine imaging technology, which involves radiolabeled leukocytes and antibody imaging, has developed into an emerging and insightful tool in diagnosing infection, particularly osteomyelitis of the lower extremities.²³ Nuclear medicine imaging differs from other diagnostic modalities in that it represents metabolic information, not anatomic information (i.e. CT or MRI), occurring within the human body.²⁴

   Technetium (⁹⁹mTc), indium (¹¹¹In), gallium (⁶⁷Ga) and fluorine (¹⁸F) are the most widely available isotopes used in nuclear medicine infection imaging. Technetium in particular is advantageous in nuclear medicine imaging because it emits low-energy gamma radiation, which minimizes patient exposure, maintains a short half-life within the human body and displays better imaging quality than most isotopes.²³

   Due to these qualities, technetium was the optimal choice in the development of technetium-99m-d,l hexamethyl propylene amine oxime (Tc-HMPAO), better known by the trade name Ceretec (GE Healthcare).²³ The Tc-HMPAO imaging combines the superior imaging noted with the ⁹⁹mTc triple phase bone scan with the ability to precisely identify localized regions of white blood cell accumulation commonly visible in osteomyelitis.²³ Tc-HMPAO has become more commonly used than other white blood cell labeled isotopes for these reasons. The Tc-HMPAO has gained popularity due to its unique advantage in differentiating aseptic inflammation (i.e. Charcot neuroarthropathy) versus infection (i.e. osteomyelitis).²⁵ Smaller prospective studies confirm that white blood cell labeled scintigraphy is comparable to that of MRI in sensitivity and specificity in the diagnosis of osteomyelitis.²⁶