Clinical Applications of MRI

Orbit and Optic Nerves:
Selection of an imaging plane other than axial (eg. an oblique plane along the axis of the optic nerve) allows better definitions of a lesion. With the use of specialty surface coils, not only can subtle pathological changes be detected, but high resolution images are achieved without the risk of exposure to potentially cataract-inducing X-rays. Because of these advantages, MRI provides improved reliability in determining the presence and extent of tumor, granulomatous disease (eg. sarcoid), infection and hemorrhage.

Applications Include:

Tumors and other mass lesions involving
· the globe
· retina
·retro-orbital space
Trauma, hemorrhage, blowout fractures
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Abdomen:
The advent of special and fast scanning techniques -breath-holding studies are now possible -reduces motion infarct, permitting MRI to complement and, in many cases, surpass CT.

Given that CT misses between 20 to 30% of liver metastases, improving detections is crucial since cancer metastases to the liver is ten times more frequent than in other organs. Therefore, MRI is an excellent screening study for the liver because of its great sensitivity in detecting lesions, especially metastases.

It is very specific for cavernous hemangioma (the most common hepatic neoplasm) eliminating the need for liver biopsy with this diagnosis. MRI is also useful in detecting and monitoring the progress of other diseases such as hepatitis, hemochromatosis, the spread of intra-abdominal tumors, renal vein thrombosis, inferior vena cava, tumor invasion, venous flow pattern and portal vein obstruction. MRI is gradually developing a larger role in the diagnosis of adrenal, renal and pancreatic masses as well as all types of retroperitoneal disease.

Applications Include:

Pelvis/Genitourinary System:
MRI offers an advantage over CT in the pelvis because of its greater tissue sensitivity, absence of bone artifact and ability to acquire multiplanar views. Lack of ionizing radiation makes MRI a natural tool for the study of the reproductive organs and pelvic contents. In some instances, where ultrasound has demonstrated a pelvic mass of indeterminate signal, MRI has clarified its adnexal or uterine location. MRI aids in the staging of carcinoma of the endometrium, cervix, prostate and rectum. In the differentiation of renal masses, renal vein invasion or thrombosis, tumor extension into the inferior vena cava, renal hilar and periaortic lymphadenopathy are well-visualized with MRI.

Applications Include:

Thorax and Mediastinum:
With the use of cardiac gating and fast scanning techniques, MRI studies of the chest have become the procedure of choice in many instances. IN particular, MR images of the hilum, mediastinum, pericardium and its contents have substantially improved in terms of tissue contrast, differentiation and reslution. Because of the ability to distinguish vessels from soft tissue masses without the use of IV contrast agents and without being plagued by streak artifacts, MRI is proving useful in diagnosing mediastinal and hilar masses as well as lymph node enlargement.

MRI appears to be superior in the differential diagnosis of hilar and mediastinal vascular lesions (eg. compression, invasion, obstruction), normal vessels, nonvascular lesions and lymph nodes. MRI is no less capable than CT in diagnosing abnormally enlarged mediastinal lymph nodes or mediastinal masses, but does fall short in being able to consistently define calcifications.

Even without cardiac gating, small hilar and mediastinal lymph nodes, the esophagus, thymus and thyroid glands are well resolved with MRI. Clarification of pleural thickening and effusion, obstructed lung vs. tumor extension, often can be useful in the treatment planning of malignant disease. Gating can be useful in suspected cases of vascular lesions, paracardiac, mediastinal or lung masses.

Applications Include:

Spine and Spinal Cord:
MRI yields diagnostically superior images of the cervical, thoracic and lumbosacral spine without the distortion from bone artifacts that CT experiences. It provides clear visualization of the spinal cord, CSF spaces, spinal nerves and roots, intra-spinal fat and ligaments, neural formina, vertebral bodies, facet joints, vertebral marrow spaces and intervertebral discs.

Using multiplanar imaging, a single, non-invasive MRI study for many disorders of the spine can be substituted for a CT and myelogram (which has the inherent risk of intraspinal contrast agents and CSF leaks). In particular, MRI is considered to be the procedure of first choice of myelophatic disorder at all levels of the spine to rule out, for example, intra or extradural primary or metastatic tumors affecting the spinal cord with or without vertebral involvement, for Chiari malformation, syringomyelia and to investigate radiculopathies secondary to suspected disc disease at all levels.

Gadolinium contrast imaging has had a significant impact in increasing the conspicuity of lesions and for differentiating recurrent herniated discs from post-operative scarring, an extremely difficult clinical problem not screened well by CT even with iodinated contrast enhancement. MRI should now be seen as the primary investigation for such patients.

Applications Include:

Musculoskeletal System - Extremities:
The advantage of MRI over CT and other imaging modalities in evaluating pathological disorders of musculoskeletal tissue derives from the superior depiction of contrast between muscle, fat, vessels, tendons, ligaments, cartilage, synovium, cancellous bone and marrow space, all without bone artifact or need for invasive procedures.

Disorders include bone and soft tissue neoplasms, different stages of infection and osteomyelitis, many types of soft tissue trauma, early bone avascular necrosis and cartilage and ligament injuries, especially of the knee, shoulder hips and ankles. With the use of the high resolution surface coils, fine details are revealed of the patella, ligaments, menisci and cruciates of a diagnostic quality sufficient to replace arthrography and focus artroscopy in most knee injury cases.

MRI has been accepted as the procedure of choice in examining suspected cases of aseptic/avascular necrosis of the hips, knee, ankle, shoulder, and wrist. It is rapidly gaining a dominant role in evaluating rotator cuff injuries of the shoulder and complex abnormalities of the hand and wrist, including triangular cartilage injuries, avascular necrosis of lunate and scaphoid, and carpal tunnel syndrome.

Applications Include:

Head and Neck:
With the application of improved surface coil techniques, MRI is emerging as the preferred imaging study for many of the extracranial head and neck disease processes that in the past required CT.

MRI surpasses CT in its ability to show abnormal soft tissue extensions, and in its ability to differentiate vascular from nonvascular structures or to delineate subtle differences in soft tissue boundaries, pathological changes and tumor extensions. This improved sensitivity, coupled with multiplanar imaging, provides the clinician with views most appropriate for optimizing diagnosis treatment and planning, and for carrying out and monitoring therapy (eg. choosing the appropriate surgical approach of designing the most effective radiation ports). A more accurate determination of tumor involvement can, for example, preserve voice function by avoiding the need for total laryngectomy; it can rule out surgery in cases of unresectable tumor because of spread of the tumor to adjacent organs.

Applications Include: