3D sequence MRI in the assessment of meniscofemoral and ligament lesions of the knee MA.Chaabouni,A.Daghfous, A.Ben Othman,L.Rezgui Marhoul Radiology departement Trauma center, Tunisia MK9

INTRODUCTION INTRODUCTION Magnetic resonance imaging (MRI) is sensitive and specific in the diagnosis of internal derangements of the knee. The fast spin-echo (SE) intermediate-weighted sequence widely used to evaluate ligaments, tendons, and fibrocartilage owing to its favorable contrast and signal-to-noise ratio. Multiplanar imaging or 3D sequence, which usually takes longer, is often used for knee MR imaging because of the necessary assessment of complex musculoskeletal structures. Volumetric imaging also offers an opportunity to reduce the imaging time by allowing multiplanar reformations.

Our objective is to determine whether 3D sequences can improve the diagnostic performance of a routine MR protocol for detecting meniscal and ligament lesion of the knee.

MATERIALS AND METHODS MATERIALS AND METHODS Retrospective study : 56 patients who had knee MRI 1,5 Tesla for suspected meniscal and/or ligament lesions. Two years: done between January2010 and December Our protocol uncludes conventional sequences (coronal, sagittal and axial Proton Density Fast-Spin Echo and sagittal T 1) and systematic sequence 3D thin sections. We propose it as the basis for the analysis of meniscal and ligament lesions.

RESULTS RESULTS All meniscal and ligament tears was shown equally well with 2D and 3D sequences. The 3D sequence allows a more precise analysis of these lesions. Of the 56 cases studied by MR imaging,14 were normal,24 had meniscal tears,15 had ACL tears and 3 had PCL tears. Nine of the menisci were longitudinal tears, 6 vertical tears, 4 radial tears, 3 complex tears and 2 seal cove tears.

Fig.1: A 34 -year-old female patient with PCL tear ( ) of the right knee Sagittal images obtained with 2D FSE (a) and 3D sequences (b) at 1,5T Fig.1: A 34 -year-old female patient with PCL tear ( ) of the right knee Sagittal images obtained with 2D FSE (a) and 3D sequences (b) at 1,5T a b

Fig.2: A 38-year-old male patient with a complex tear of the medial meniscus posterior horn. ( ) Sagittal images obtained with 2D (a) and 3D sequences (b) at 1,5 T. Axial images obtained with 2D (c) and 3D FSE sequences (d) at 1,5T. a b c d

a b c d Fig.3:A 45-year-old male patient with a longitudinal tear of the medial meniscus posterior horn. Sagittal and axial images obtained with 2D (a,c) and 3D FSE sequences (b,d )at 1,5T. The tear is not visualised on the axial 2D FSE sequence but well visualised on 3D

Fig.4: A 21 -year-old female patient with a seal cove tear of the medial meniscus posterior horn ( ) Coronal and sagittal images obtained with 2D (a,c) and 3D FSE sequences (b,d) at 1,5T. a b c d

Fig.5: A 27-year-old male patient with ACL tear of the left knee. Sagittal images obtained with 2D (a) and 3D FSE sequences (b) at 1,5T. a b

DISCUSSION DISCUSSION The described 3D isotropic fast SE intermediate weighted MR sequence enables thin-section data acquisition without intersection gaps and multiplanar image reformation in standard and nonstandard planes that may be helpful for the detection and analysis of complex structures. The 3D Fourier transform acquisition is conceptually attractive for musculoskeletalMR imaging because it facilitates image reformation in complex oblique planes after image acquisition..

Duc et al (28) reported 3D isovoxel true fast Imaging with steady-state precession to have sensitivities, specificities, and accuracies of 80%, 95%, and 90%,respectively, for the diagnosis of ACL tears; 100%, 82% and 90%, respectively, for the diagnosis of MM tears; and 83%, 83%, and 83%, respectively for the diagnosis of LM tears. While image quality consistently scored lower with the 3D compared with the 2D FSE sequences, the diagnostic performance was similar, though radiologists felt more confident diagnosing abnormalities with the 2D sequences.

In our serie, both the 2D and the 3D sequences provided subjectively high-quality images with comparable anatomic detail. All meniscal and ligament tears was shown equally well with both techniques. John and all showed that for meniscal tears, the superior sensitivity of the 3D sequence became evident.

The thinner slice thickness and resultant dimunition in volume-averaging may have been responsible for this observation, especially in the case of small tears. However, the Heightened sensitivity to intrameniscal signal afforded by the 3D technique also contributes to its decreased specificity relative to SE imaging.

Because a greater volume of signal could be identified within the meniscus, it often became more difficult to determine whether the abnormality communicated with the meniscal surface, thus differentiating internal degeneration from actual tear. Long scan times have limited the clinical utility of 3D spin- echo imaging implementations.

CONCLUSION CONCLUSION Although the fact that 3D isotropic fast SE intermediate- weighted MR imaging of the knee is a real plus for the analysis of cruciate ligament and meniscal tears, it yields accuracy that is not significantly different from the accuracy of 2D fast SE MR imaging.