Neurologic Imaging
In the realm of neuro imaging of the brain and spine, standard pulse sequences in various imaging planes are routinely performed, tailored to the specific clinical question or possible diagnosis. In addition, the use of single- and/or multi-shot diffuse-weighted imaging allows for detection of regions of acute ischemia (decreased blood flow) in the brain, and potentially the spinal cord, within minutes of an ischemic event. Early diagnosis makes treatment, using various medical therapies, of patients with acute stroke, or "brain attack," possible within the critical three-hour treatment window. High-resolution MR angiography is now considered routine, and is further discussed in the section on vascular imaging.

State-of-the-art imaging of the cervical, thoracic, or lumbar spine is now performed with MRI for the assessment of abnormalities within the spinal cord, exiting nerve roots or adjacent discs and bony structures. MR myelography has essentially replaced conventional myelography for the majority of indications.

Cardiac Imaging
It is not easy to take pictures of the human heart, since it beats at roughly sixty to eighty times per minute. With continued equipment and computer advances including improvement in gradient systems, pulse sequence design, and more rapid breath-hold ECG-triggered scanning techniques, cardiac MRI has come of age. This is good for patients and doctors alike, because difficult diagnoses can be made more easily, and treatment can be tailored to the individual patient more quickly.

Cardiac MRI can be used to evaluate several important aspects of heart structure and function. The next several paragraphs will address these capabilities.

MRI can be used to calculate ejection fraction, left ventricular function, and to assess wall motion more accurately and reproducibly than echocardiography. Stroke volume, end-diastolic and end-systolic volumes, cardiac output, and left ventricular mass and wall thickness can be readily measured. Valvular assessment for regurgitation can be performed using cine multi-phase techniques. The regurgitant fraction of a "leaky valve" can be calculated, and valve disease progression accurately assessed, over serial exams. Valvular stenosis can be evaluated, flow velocity can be measured through a stenotic valve, and valve area can be calculated, using phase-contrast quantitative flow techniques.

MRI is the diagnostic method of choice for the evaluation of arrhythmogenic right ventricular dysplasia, a potentially life-threatening disease process. Using black blood techniques, fatty and/or fibrous tissue replacement of the right ventricular myocardium can be assessed. Using cine multi-phase bright blood sequences, abnormal contractility in the diseased right ventricular segments can also be visualized.

Perhaps the most challenging, but equally important, aspect of cardiac imaging is evaluation of the coronary arteries – the small blood vessels that supply the heart muscle, itself, with oxygen and nutrients. With the advent of improved ECG-gating techniques, and navigator respiratory triggering in end-expiration, imaging of the proximal one-third of the coronary arteries can now be accomplished non-invasively. This is helpful in the evaluation of patients with possible abnormal origin and course of the coronary arteries, and in the assessment of proximal coronary artery blockage or stenosis. In the future, we hope that MRI will permit detailed images of smaller, more distal coronary artery segments.

In patients who have had a myocardial infarction (heart attack), MRI can be used to identify regions of the heart with abnormal muscle contraction, and to further assess these regions for viability. Delayed enhancement techniques allow differentiation between regions of scar (dead muscle) and regions of "stunned or hibernating" (not dead) myocardium. The size of an infarct and the extent of wall involvement (transmural vs. subendocardial) can also be well seen. This is very beneficial in selecting those patients who would best benefit from a revascularization procedure, such as balloon angioplasty, stent placement, or bypass surgery.

MRI can also accurately assess pericardial thickness and abnormalities of diastolic filling in patients with possible constrictive pericarditis, and help in differentiating these patients from those with restrictive cardiomyopathy. The various forms of cardiomyopathy and associated functional abnormalities can also be evaluated by MRI. In addition, cardiac, pericardial, and paracardiac masses can be well visualized and characterized.

Vascular Imaging
MRI offers various methods for evaluating the vascular system. These include techniques that use the signal from flowing blood (time-of-flight and phase-contrast MR angiography), as well as bolus contrast-enhanced breath-hold scans obtained immediately after intravenous gadolinium administration. These techniques, singly or in combination, allow for assessment of the vascular system non-invasively from head to toe.

In the brain, MR angiography is routinely used for the assessment of intracranial aneurysm, vascular malformation, or focal areas of vascular stenosis or occlusion. MR angiography of the carotid bifurcation regions is now routinely performed as a screening examination for patients with suspected carotid artery disease prior to endarterectomy.

MRI, including MR angiography, is the imaging method of choice in the evaluation of the thoracic aorta. The multi-planar capability and ECG gating provided by MRI allow for optimal evaluation of aneurysm, aortitis, intramural hematoma, dissection, aortic valvular involvement, coarctation, and congenital anomalies of the arch and great vessels. The abdominal aorta, including its major branch vessels, is readily visualized using bolus contrast-enhanced breath-hold scans. Stenosis or occlusion within the abdominal aorta, visceral vessels (celiac/superior mesenteric artery), and renal arteries is clearly depicted. We feel that bolus gadolinium-enhanced MR angiography provides the most accurate non-invasive method available today for the evaluation of renal artery stenosis, and should replace nuclear medicine scanning and Doppler ultrasound studies for this purpose. Multiple renal arteries are also accurately visualized.

Bilateral lower extremity run-off evaluation using contrast-enhanced stepping table techniques can be performed in lieu of conventional lower extremity angiography for the diagnosis of peripheral vascular disease. This technique allows for improved visualization of distal vessels below the levels of occlusion, when compared with conventional angiography studies. In addition, the gadolinium contrast agent is "renal safe," even in patients with underlying renal insufficiency or diabetes.

Abdominal/Pelvic Imaging
MRI of the abdomen and pelvis has markedly improved with the advent of improved breath-hold, respiratory-triggered, free breathing, and robust fat saturation techniques. The multi-planar capability and tissue specificity of MRI affords an added benefit in evaluating pathology when compared to CT.

Evaluation of the biliary tree can be easily performed with two-dimensional, radial two-dimensional, and three-dimensional high-resolution magnetic resonance cholangio-pancreatography (MRCP). MRCP provides a cost-effective, non-invasive alternative for the work-up of diseases of the bile and pancreatic ducts, as well as the gallbladder. It can be used to select those patients who require more invasive biliary tract evaluation, and treatment with endoscopic retrograde cholangio-pancreatography (ERCP).

MRI of the pelvis is an underutilized, but very effective, imaging tool, particularly in evaluation and characterization of abnormalities of the female pelvis (gynecologic imaging). It is useful in the assessment of the uterus and cervix for congenital anomalies, masses, and adenomyosis. The adnexal regions are well imaged for ovarian and adnexal masses, and endometriosis.Tissue specificity of MRI allows for characterization of masses with fat (teratoma/dermoid), and hemorrhage (endometrioma/hemorrhagic cyst).

MR urography is also easily performed as part of an evaluation of the kidneys and urinary tract, using either urine or gadolinium as the contrast agent to opacify the collecting system, ureters, and urinary bladder.

Musculoskeletal System
After plain radiographs have been performed, MRI has been established as the imaging procedure of choice for the musculoskeletal system, if additional imaging evaluation is needed. This is based on the ability of MRI to non-invasively evaluate bone marrow, cartilage, menisci, ligaments, muscle, and tendon in one examination. Advances in musculoskeletal MR include improved sequences for high-resolution cartilage imaging to guide and follow treatment. MR arthrography is now also routinely used to evaluate the shoulder and wrist joints for subtle abnormalities. Diffusion-weighted imaging can be helpful in differentiating malignant bone marrow processes from post-traumatic marrow edema, such as that seen in spinal vertebral body osteoporotic compression fractures.