SCIENTIFIC PRINCIPLES OF MRI

Scientific Principles Of MRI



Scientific Principles Of MRI

Disorders of the knee are a main source of referrals to the musculoskeletal radiologist (Haramati, 2003). Most cases involve suspected abnormalities within the joint, either following an acute injury or related to a more insidious development of symptoms (Dorsay, 2003). Other common causes of referral are anterior knee pain, and focal and diffuse swellings. Magnetic resonance imaging (MRI) is the technique of choice for assessing the internal structures (McNally, 2002: 570).

Articular cartilage defects are a frequent finding on MRI of the knee. The sensitivity of MRI is variable and is highly dependent on the sequences used. As surgical techniques for articular cartilage defects are gaining popularity, the use of cartilage-specific sequences has increased. Proton density with fat suppression, which is widely used as part of a routine knee protocol, is suitable for articular cartilage defects and has the advantage of being very sensitive for the associated subchondral oedema (Miller, 2001: 424). Several high-resolution gradient echo sequences, such as true fast imaging with steady state precession (true FISP) or spoiled gradient recalled acquisition in steady state (SPGR) with fat suppression, show the articular cartilage to good effect (Barry, 2005: p365).

Figure 1. True FISP image showing good contrast between the cartilage and fluid. There is a full thickness defect in the articular cartilage of the medial femoral condyle. (Source: ww.tripdatabase.com/doc/814875)

The nodular form of pigmented villonodular synovitis is another synovial-based lesion that may present as a mass or with symptoms of internal derangement (McNally, 2002: 571). A common site for this lesion is Hoffa's fat pad. On MRI, the mass will be seen to contain some loss of signal intensity on T2 weighted images, representing a combination of fibrosis and scattered haemosiderin deposits (McNally, 2002: 573). Excision is usually curative. Bony lesions should be considered as a cause of a focal swelling around the knee. Osteochondromata are common, and imaging beyond the plain film is particularly used in symptomatic lesions to exclude malignant transformation of the cartilage cap. The posterior aspect (Haramati, 2003)

Figure 2. Lipoma arborescens. T, weighted axial image showing fatty synovial villous masses projecting into the joint (arrows).

(Source: ww.tripdatabase.com/doc/814875)

Anterior knee pain is a common complaint, particularly in adolescents and young females. The cause is often not apparent clinically and most patients are treated conservatively without resort to imaging. Most cases are related to the patellofemoral joint. The main purpose of imaging is to exclude other specific conditions, such as osteochondral defect or patellar tendinopathy, and to identify any abnormal morphology of the patellofemoral joint that may be amenable to surgery. Plain films provide limited information. MRI is sensitive for excluding significant unexpected pathology and can be used to assess the patellofemoral anatomy and patella subluxation. Ultrasound is useful in diagnosing suspected patellar tendinosis (Barry, 2005).

This condition, which affects athletic young adults, is an overuse syndrome of the proximal patellar tendon, possibly caused by impingement of the tendon on the inferior pole of the patella (Dorsay, ...