MRI knee

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How to read MRI of the Knee By Dr :Dina Moghazy Lecturer of radiodiagnosis Tanta university :

How to read MRI of the Knee By Dr :Dina Moghazy Lecturer of radiodiagnosis Tanta university

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Bones A knee MRI will include parts of the lower femur, upper tibia, upper fibula and the patella. The knee MRI can detect bone bruises, fractures, cysts, tumors, infection and dislocations. Tendons and Ligaments Your knee has a complex set of tendons and ligaments that MRI can evaluate. ACL ,PCL ,MCL and LCL .The extensors of the knee are composed of the quadriceps tendon, Patella and patellar tendon. Meniscus Mensical tears are manifested by linear signal that traverse the mensicus . Soft Tissues This refers to the muscles and tissues around knee. A knee MRI scan will show parts of the thigh muscles and muscles of the upper calf area. The MRI can detect muscle tears, tumors and infection. It can also detect a common fluid collection .

PROTOCOLS:

PROTOCOLS What is meant by T1 and T2 ? T1 and T2 refer to physical properties of the tissue after exposure to RF pulses after predetermined time interval. Different tissue have different T1 and T2 properties, based on the response of their hydrogen nuclei to rediofrequency pulses imposed by the magnet. These differential properties will appear by setting equipment parameter (TR and TE ),TR is the time to repeat or the time between radiofrequency pulses, TE the time between the RFP and the signal or the image both are expressed in milllisecond (ms). How can you tell if you are looking at T1 or T2 images ? Looking for the TE and TR numbers on the image: Low TE: 20 ms , and high TE : 80 ms .Low TR :600 ms and high TR around 3000 ms . T1 has low TE and low TR and for T2 both are high .PD has low TE and and high TR . Fat is bright in T1 and less bright in T2 .Water is dark in T1 and bright in T2 What is fat suppression? It is special MR techniques to eliminate bright signal of fat by repeated RFP targeting fat protons result in relative absence of signal from fat . Fat suppression accentuates bone marrow and soft tissue edema on fluid-sensitive sequences. Examination of knee : *a combination of weighted proton density (PD) and T2-weighted fast spin echo sequences with and without fat suppression are used to provide excellent anatomic detail and localize pathology. Fat suppression accentuates bone marrow and soft tissue edema on fluid-sensitive sequences, and non – fat-suppressed images increase conspicuity of bone marrow abnormalities on short echo time (TE) sequences. * In general, optimal evaluation is achieved when the imaging planes are oriented perpendicular to and parallel to the long axis of the structure in question. *Oblique sagittal image acquisition oriented parallel to the lateral femoral condyle, which optimizes evaluation of the anterior cruciate ligament (ACL), horns of the menisci, femorotibial joint and femoral trochlear articular cartilage, cruciate ligaments, and extensor mechanism. *The coronal plane of imaging is preferred for evaluation of the body of the menisci, and medial and lateral stabilizing structures. *The axial plane is used to evaluate the patellar articular cartilage,quadriceps tendon, and medial and lateral stabilizing structures.

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On the left a different entity, but the patient had the same symptoms   Acute onset of medial pain   There is diffuse marrow edema on T2W-image   On T1W-image the focal abnormality is not directly subchondral   The abnormality on the T1 is more inside the edema   On the T1W-image a dark line is visible indicating a insufficiency fracture  

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in the same patient the MRI shows an obvious tibiaplateau fracture On the left another patient with knee pain after trauma,the x-rays are normal

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Normal and abnormal bone marrow In adults the bone marrow is largely composed of fat. Normal islands of red marrow may produce confusing images   Red bone marrow can be pronounced in young women, cigarette smoking, high altitude, or for no reason at all

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A case with abnormal marrow In this case the marrow is too dark on T1 and T2 due to iron deposition in the marrow after many blood transfusions in a patient with hemosiderosis

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Anterior Cruciate Ligament The ACL is composed of 3-5 layers of fibers. The ACL courses from the posteromedial aspect of the lateral femoral condyle to insert anterolateral to the anterior tibial spine. Between the fibers there can be fat or synovium or sometimes a little bit of fluid. This explains why the ACL is not black on PD-images. Do not look at the ACL on PD-images only because this may give a false impression of pathology   Only look at the ACL on T2W-images and even on these images the ACL does not have to be entirely black.   Criteria for the normal ACL are Fiber-orientation as steep or steeper than the intercondylar roof . Fibers all the way from the tibia to the femur bone bruises can be a helpful secondary sign

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The torn PCL is widened and contains increased signal

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The superficial medial collateral ligament (MCL) extends from the medial epicondyle to insert not just near the joint but 7 cm below the joint space It is closely applied to the medial meniscus . The medial collateral ligament (MCL) is not visualized .

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Fig 2    Coronal MRI demonstrating complete grade 3 MCL tear from the femoral origin (black arrow)

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Imaging of mensci

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6-LM

Grading of meniscal tears on MRI :

Grading of meniscal tears on MRI

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A peripheral longitudinal tear extending to the tibial surface within the posterior horn of the medial meniscus!

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Fat-suppressed proton density-weighted (C) sagittal and (D) coronal images reveal a horizontal tear of the posterior horn of the medial meniscus (arrows), extending to the tibial surface.

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A coronal image from another patient with a medial meniscal tear demonstrates associated severe medial subluxation of the meniscal body (arrow). Fat suppressed proton density-weighted reveal a tibial sided flap tear of the body of the medial meniscus, with displacement of the undersurface component (arrows) into the inferior gutter. 

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the preoperative study, a large displaced "handle" (arrow) from the body of the lateral meniscus is seen near the intercondylar notch. Only a small peripheral rim of meniscal tissue (arrowhead) is present at the native site of the lateral meniscus. Two months later, the post-operative image (T) reveals a repaired, normal appearing lateral meniscal body (arrow), with resolution of the previously seen displaced fragment.

Bucket  Handle  Tear:

Bucket   Handle   Tear A displaced longitudinal meniscal tear is termed a bucket handle tear since the displaced central fragment resembles the handle of a bucket. They frequently occur in younger patients secondary to significant trauma and there may be an associated ACL tear. The displaced fragment often lies in the intercondylar notch, anterior to the posterior cruciate ligament (PCL), as seen in example 1,  

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Normal Extensor mechanism The extensor mechanism of the knee is composed of the quadriceps muscle and tendon, the patella and the patellar tendon. The quadriceps tendon is made of four tendons but comes in three layers on sagittal images   It has a broad attachment all the way from the front of the patella almost to the back   The tendons of the quadriceps as well as the patellar tendon are homogeneous in signal but don't have to be black on PD-images,They have a sharp posterior demarcation

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Tear of patellar tendon .

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Patellar dislocation Normal anatomy The patellar cartilage is the thickest in the body. It should have smooth contours   The most important part of the medial retinaculum is the medial patellofemoral ligament which inserts all the way posteriorly just in front of the MCL

Cysts, Bursae and Recesses :

Cysts, Bursae and Recesses There are about 12 named bursae and recesses in the knee, Some very common and others uncommon, These are synovial lined structures, Visualization of these potential spaces is commonly due to pathologic fluid accumulation (bursitis).   . The semimembranosus-gastrocnemius bursa, located within the posteromedial aspect of the knee,communicates with the knee joint in a majority of individuals, and is referred to as a popliteal (Baker ’ s) cyst. Perimeniscal cysts are formed by fluid being pumped through a meniscal tear into the perimeniscal tissue.They occur in both lateral and medial menisci and may be painful

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These bursae are all named by the structures next to them . So a bursitis of the bursa between the deep MCL and the superficial MCL is called a medial collateral ligament bursitis . Prepatellar bursitis On the left the typical imaging findings of prepatellar bursitiss

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Thank you