MRI In Orthopaedics

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Information about MRI In Orthopaedics
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Published on March 2, 2014

Author: mittal87

Source: authorstream.com

MRI In Orthopaedics: MRI In Orthopaedics By Dr ANKUR MITTAL Introduction: Revolutionised musculoskeletal imaging. MRI has superseded older imaging methods, such as myelography , arthrography , and angiography. In some areas, such as the knee and shoulder, MRI has become a powerful diagnostic tool. Introduction Principles: MRI is based on the reemission of an absorbed radio frequency ( rf ) signal while the patient is in a strong magnetic field. An external magnetic field is usually generated by a magnet with field strengths of 0.2 to 1.5 tesla (T). The system includes a magnet, rf coils (transmitter and receiver), gradient coils, and a computer display unit with digital storage facilities. Principles Principles(Contd): Images are created by placing the patient in a strong magnetic field (approximately 30,000× stronger than the earth's magnetic field). The magnetic force affects the nuclei within the field, specifically the nuclei of elements with odd numbers of protons or neutrons(Hydrogen), which is plentiful in water and fat. Principles( Contd ) Principles(Contd): When the patient's tissues are subjected to this strong magnetic field, protons align themselves with respect to the field. In this steady state, a radiofrequency pulse is applied, which excites the magnetized protons in the field. After application of this pulse, a receiver coil or antenna listens for an emitted radiofrequency signal that is generated as these excited protons relax or return to equilibrium. This signal, with the help of localizing gradient fields and Fourier transformation, creates the MRI image. Principles( Contd ) Principles(Contd): Principles( Contd ) T1 and T2 weighed images: The T1 relaxation time ( longitudinal relaxation time) - used to describe the return of protons back to equilibrium after application and removal of the rf pulse. - 300-2000msec - Provide good anatomic detail T2 relaxation time (transverse relaxation time) - used to describe the associated loss of coherence or phase between individual protons immediately after the application of the rf pulse. - 30-150 msec - used for evaluation of pathologic processes. T1 and T2 weighed images Fat suppression technique: Frequency-selective (chemical) fat saturation Inversion–recovery imaging Opposed-phase imaging Fat suppression technique MRI in spine: MRI allows a noninvasive evaluation of the spine and spinal canal, including the spinal cord. Spinal examinations usually include series obtained in axial and sagittal planes. Coronal images may be helpful in patients with scoliosis. MRI in spine Intervertebral disc disease: Most common indication for MRI of the spine The combination of high soft-tissue contrast and high resolution allows ideal evaluation of the intervertebral discs, nerve roots, posterior longitudinal ligament, and intervertebral foramen. Additionally, MRI provides excellent delineation of the spinal cord. Intervertebral disc disease Normal disc: Low signal intensity on T1W images, slightly lower signal than adjacent normal red marrow and very similar to muscle. T2W images show diffuse high signal intensity throughout the disk except for the outer fibers of the annulus, which are homogeneously low signal intensity Normal disks typically do not extend beyond the margins of the adjacent vertebral bodies; however, diffuse extension beyond the margins by 1 to 2 mm may occur in some histologically normal disks Normal disc Abnormal nucleus: MRI shows the intranuclear cleft as a horizontal, low signal intensity line that divides the disk into upper and lower halves on T2W sagittal images. Eventually, there will be a diffuse decreased signal intensity on T2W images from the increased collagen content in the nucleus. The disk progressively loses height with increasing degrees of degeneration. Abnormal nucleus Abnormal Annulus: Aging and biochemical changes in the annulus are associated with the development of multiple, focal tears. MRI of annular tears shows focal areas of high signal intensity on T2W images or on contrast-enhanced T1W images. Radial tears may be seen on T2W sagittal images within the posterior annulus as globular or horizontal lines of high signal intensity. On axial images, radial tears may be seen as focal areas of high signal intensity that parallel the outer disk margin for a short distance. Radial tears or fissures on MRI also are referred to as high intensity zones. Abnormal Annulus Abnormalities of disc morphology: Disc bulge - A diffusely bulging disk extends symmetrically and circumferentially by more than 2 mm beyond the margins of the adjacent vertebral bodies. - This diagnosis is based on axial and sagittal images by comparing the size of the disk with the size of the adjacent vertebral bodies and determining if the central canal and neural foramina are narrowed by the disk Abnormalities of disc morphology PowerPoint Presentation: Disc protrusion - A disk protrusion is a focal, asymmetric extension of disk tissue beyond the vertebral body margin, usually into the spinal canal or neural foramen. - The base (the mediolateral dimension along the posterior margin of the disk) is broader than any other dimension PowerPoint Presentation: Disc extrusion - disruption of the outer fibers of the annulus, and the disk abnormality usually is greater in its anteroposterior dimension than it is at its base ( mediolateral dimension). PowerPoint Presentation: Sequestered Disc - When extruded disk material loses its attachment to the parent disk, it is called a sequestered fragment . - These fragments may migrate in a cranial or caudal direction with equal frequency and generally remain within about 5 mm of the parent disc. PowerPoint Presentation: Disk-related myelopathy - High signal intensity areas on T2W images can be seen within the spinal cord at the point of spinal stenosis secondary to a disk bulge or extrusion. - This high signal intensity may be from focal myelomalacia owing to ischemia to the cord Location of disc abnormalities: Location of disc abnormalities PowerPoint Presentation: Structres which mimicks extruded and sequestrated disc - Synovial cyst - Conjoined nerve root - Arachnoid diverticulum - Perineural ( Tarlov ) cyst - Nerve sheath tumors - Small epidural hematoma PowerPoint Presentation: Postoperative Back Pain - Gadolinium contrast MRI is useful to differentiate epidural fibrosis and persistent extruded disc. - After gadolinium administration, repeat T1-weighted images typically show enhancement of scar or fibrosis PowerPoint Presentation: Triad of vertebral body end plate enhancement, disc space enhancement, and enhancement of the posterior longitudinal ligament is highly suggestive of postoperative discitis Spinal tumours: MRI has proven valuable in the assessment of spinal neoplasms . Excellent delineation of vertebral body marrow allows detection of primary and metastatic disease with high sensitivity on T1-weighted sequences. Vertebral tumor foci appear as discrete areas of diminished T1 signal. Spinal tumours Spinal Trauma : Useful in patients with - Suspected spinal cord injury - Epidural hematoma - Traumatic disc herniation - Ligamentous injury in acute stage Spinal Trauma MRI in knee: Normal meniscus - Best evaluated in cross section on sagittal images - The normal meniscus is devoid of signal on all imaging sequences, with the exception of children and young adults, who typically have some intermediate to high signalposterior horns near the meniscal attachment to the capsule - Menisci appear as dark triangles in the central portion of the joint and assume a “bow tie” configuration at the periphery of the joint. MRI in knee PowerPoint Presentation: Meniscal tears - If high signal clearly disrupts an articular surface of the meniscus it is a torn meniscus. - If high signal comes close to the articular surface it is intrasubstance degeneration or myxoid degeneration. - grade 1 (globular), grade 2 (linear), and grade 3( Articular extension) Abnormalities With Absent Bow Tie Sign: Bucket-handle tear Radial tear Medially flipped flap tear Meniscal cyst Abnormalities With Absent Bow Tie Sign Discoid meniscus: When the “bow tie” configuration of the lateral meniscus in the sagittal plane on more than three slices indicates a discoid meniscus Discoid meniscus Meniscal cyst: seen as discrete collections marked by fluid signal intensity that are located medially or laterally Meniscal cyst Anterior Cruciate ligament injuries: The sagittal images are prescribed in a plane parallel to the course of the anterior cruciate ligament (ACL), approximately 15 degrees internally rotated to the true sagittal plane. The normal ACL has straight, taut fi bers that run parallel to the roof of the intercondylar notch. It typically has a striated appearance with some high signal within it, especially at its insertion on the tibia. Fibers should be parallel to the roof of the intercondylar notch. Anterior Cruciate ligament injuries Anterior Cruciate ligament injuries: Reliable signs of ACL rupture include an abnormal horizontal course, a wavy or irregular appearance, or fluid-filled gaps in a discontinuous ligament. Chronic tears can reveal ligamentous thickening without edema or, often, complete atrophy. In acute injuries, bone contusions are manifested as regions of edema in the subchondral marrow, typically in the lateral compartment Anterior Cruciate ligament injuries Anterior Cruciate ligament injuries: MRI can depict accurately the reconstructed ACL within the intercondylar notch and define the position of intraosseous tunnels. A thickened graft or absence of the graft on MRI suggests graft failure . Anterior Cruciate ligament injuries Posterior cruciate ligament : Posterior cruciate ligament is a gently curving band of fibrous tissue, appearing as a homogeneously hypointense structure of uniform thickness on sagittal MRI series. Discontinuity of the ligament or fluid signal within its substance indicates a tear. Posterior cruciate ligament Collateral ligament injury: Coronal plane imaging Medial collateral ligament appears as a thin dark band of tissue closely applied to the periphery of the medial meniscus. Mild injuries result in edema around the otherwise normal ligament. Severe strain or rupture causes ligamentous thickening or frank discontinuity. Although mild degrees of medial collateral ligament injury correlate well with MRI appearance, imaging is less accurate in grading more severe injuries. Injuries of the lateral supporting structures, including the fibular collateral ligament, iliotibial band, biceps femoris , and popliteus tendon, also are depicted with MRI. Collateral ligament injury Other uses of MRI in Knee: Osteonecrosis Synovial pathological conditions Osseous contusions Occult fractures Assessing complications of physeal injuries in children Osteochondritis dissecans Tears of the patellar or quadriceps tendon Osteochondral injury Other uses of MRI in Knee MRI in Hip Joint: Osteonecrosis - The most frequent indication for hip imaging is evaluation of osteonecrosis because early diagnosis is desirable. - On T1-weighted images, the classic MRI appearance of osteonecrosis is that of a geographical region of decreased marrow signal within the normally bright fat of the femoral head. This area of abnormal signal frequently is surrounded by a low-signal band, representing ischemic bone - a serpiginous line of low signal intensity surrounding an area of fatty marrow in the femoral head between the 10-o’clock and 2-o’clock positions on coronal images (usually anterior in the femoral head) is characteristic for AVN MRI in Hip Joint Osteonecrosis : The central area of necrotic bone can show various signal patterns throughout the course of the disease, depending on the degree of hemorrhage, fat, edema, or fibrosis. Flattening of the femoral head, cartilage loss, and effusion are seen in late cases of osteonecrosis . T2-weighted images reveal a second inner band of bright signal, and the resulting appearance has been termed the “double line” sign. This sign is essentially diagnostic of osteonecrosis . Osteonecrosis Mitchell MRI Staging: CLASS T1 T2 DEFINITION A Bright Intermediate "fat" signal B Bright Bright "blood" signal C Intermediate Bright "fluid or edema" D dark dark "fibrosis" signal Mitchell MRI Staging Transient osteoporosis: T1-weighted sequences depict diffuse edema as relative low signal in contrast to background fatty marrow. The edema becomes hyperintense on T2-weighted series and is accentuated when fat-suppression techniques are used. This marrow appearance has been termed bone marrow edema pattern Transient osteoporosis Other indications: Occult fractures To evaluate acetabular labrum To evaluate femuro-acetabular impingement Other indications MRI In Shoulder: Obtained in three imaging planes: (1) coronal oblique, (2) axial, and (3) sagittal oblique. The coronal oblique images are acquired with cuts made parallel to the supraspinatus tendon, alternatively, they may be acquired in a plane perpendicular to the articular surface of the glenoid . The sagittal oblique images are acquired with cuts parallel to the articular surface of the glenoid , from the scapular neck through the lateral margin of the humerus . MRI In Shoulder Pathological Conditions of the Rotator Cuff: Oblique coronal spin-echo imaging with T2 weighting optimally detects most pathological conditions of the rotator cuff. Rotator cuff tendons normally maintain low signal on all pulse sequences. Rotator cuff tears appear as areas of increased T2-weighted signal, representing fluid within the tendon substance. This signal may traverse the entire tendon substance, indicating a full-thickness tear Diffuse or focal signal abnormalities less intense than fluid should be considered tendinosis or tendinopathy Pathological Conditions of the Rotator Cuff Pathological Conditions of the Labrum: The cross-sectional anatomy of the normal labrum varies, and the adjacent glenohumeral ligaments create many potential diagnostic pitfalls. The addition of intraarticular saline or contrast material greatly improves evaluation of labral pathological conditions and the biceps tendon origin. After arthrographic instillation of saline, T2-weighted images reveal a hypointense labrum surrounded by bright fluid. A superior technique uses dilute gadolinium as a contrast agent, allowing T1-weighted imaging . Pathological Conditions of the Labrum Pathological Conditions of the Labrum: Imaging is performed in a standard position with the arm at the patient's side. Additional imaging can be performed with the humerus in abduction and external rotation for assessment of the inferior glenohumeral ligament and its origin. Anterior labral injuries are best seen in the axial plane, whereas superior labral abnormalities, or superior labral anteroposterior lesions, are best depicted in axial or coronal images. MRI arthrography - a sensitivity of 91% and a specificity of 93%. The accuracy of MRI in evaluation of superior labral anteroposterior lesions is less. Pathological Conditions of the Labrum Pathological Conditions of the Labrum: Pathological Conditions of the Labrum MRI Classification of SLAP lesion: Type I: Fraying of the free edge of the superior glenoid labrum Type II: Detachment of the superior labrum from the glenoid Type III: Bucket-handle tear of the superior labrum without involvement of the long head of the biceps tendon Type IV: Bucket-handle tear of the labrum extending into the long head of the biceps tendon MRI Classification of SLAP lesion MRI Classification of SLAP lesion: Type 5 SLAP lesion is a SLAP 2 or 3 lesion plus superior extension of a Bankart lesion . Type 6 SLAP lesions are flap tears of the superior labrum . Type 7 SLAP lesions are SLAP 2 or SLAP 3 lesions with extension into the middle glenohumeral ligament. Type 8 SLAP lesions are SLAP 2 or SLAP 3 lesions plus a posterior labral tear . Type 9 SLAP lesions are circumferential labral tears with anterior and posterior labral involvement . Type 10 SLAP lesions are SLAP 2 or 3 lesions with extension into the rotator cuff interval through the superior glenohumeral ligament. MRI Classification of SLAP lesion Other uses of MRI in shoulder: Occult fractures Osteonecrosis Long head of biceps pathology Suprascapular nerve entrapment Impingement syndrome Other uses of MRI in shoulder MRI In Foot and Ankle:  Indications Tendon injuries Bone marrow disorders Osteonecrosis Fracture Diabetic foot Ligament injuries MRI In Foot and Ankle Osteochondritis dissecans of talus: MRI of osteochondral fractures is useful to show their presence and to show if the fragment is loose (unstable) or not. MRI may show loose osteochondral fragment are high signal surrounding the fragment on T2W images, large subchondral cysts deep to the fragment, cracks in the overlying cartilage, or absence of the fragment with or without an intra- articular loose body seen Osteochondritis dissecans of talus Anderson MRI classification: Stage I - Bone marrow edema ( subchondral trabecular compression; radiograph results are negative with positive bone-scan findings) Stage IIa - Subchondral cyst Stage IIb - Incomplete separation of the osteochondral fragment Stage III - Fluid around an undetached, undisplaced osteochondral fragment Stage IV - Displaced osteochondral fragment Anderson MRI classification MRI Of Wrist and Hand: Carpal ligament disruption TFCC injury Avascular necrosis of lunate and scaphoid Tendon pathology MRI Of Elbow Useful in assessment of the biceps and triceps tendons Collateral ligament injury MRI Of Wrist and Hand Tumor imaging: MRI should only be done after X-ray. Excellent bone marrow delineation is most helpful in defining tumor extent and planning surgical and radiation therapy. Imaging should be performed in at least two planes, one of which should be axial (or transverse). This plane is most helpful in defining the relationship of lesions to nearby muscles and neurovascular structures and best shows extraosseous extension of bone tumors. Compartmental anatomy also is best shown in this imaging plane. The sagittal or coronal images define the proximal and distal extents of bone or soft-tissue involvement. Tumor imaging Tumor imaging: T1-weighted images are useful in identifying areas of marrow replacement or edema. T2-weighted sequences delineate soft-tissue extension because most neoplasms become hyperintense in contrast to surrounding muscle and fat. Tumor imaging Contra-indications of MRI: Intracerebral aneurysm clips Cardiac pacemakers Automatic defibrillators Biostimulators Certain implanted infusion devices Internal hearing aids Metallic orbital foreign bodies Relative contraindications First-trimester pregnancy Middle ear prostheses Penile prostheses Contra-indications of MRI THANK YOU: THANK YOU

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