Isotropic 3-Dimensional Fast Spin Echo Imaging Versus Standard 2-Dimensional Imaging at 3.0 T of the Knee

Abstract

To compare different fat-saturated (FS) 3-dimensional (3D) intermediate-weighted (IM-w) fast spin echo (FSE) sequences with a standard FS 2-dimensional (2D) IM-w FSE sequence using a porcine in vitro model with artificially created cartilage and meniscus lesions. Using a ceramic scalpel, cartilage lesions with different depths and sizes were created in porcine knee specimens at the patella as well as the medial and lateral femoral and tibial cartilage. In addition, lateral and medial meniscal lesions were produced. Magnetic resonance imaging was performed at 3.0 T in sagittal plane using an 8-channel knee coil. A standard FS 2D IM-w FSE sequence and 3 newly developed isotropic 3D FSE sequences: (i) non-FS echo train length (ETL): 78, (ii) FS ETL: 44, and (iii) FS ETL: 44, were used. The images were independently analyzed by 4 radiologists concerning image quality (1 = optimal image quality, 4 = substantially limited quality) and absence or presence of lesions using a 5-level confidence score (1 = definite no presence of abnormality, 5 = definite presence of abnormality). Radiologists were also asked to measure diameter and categorize the depth of cartilage lesions using a modified Noyes classification. Average scores for image quality, confidence of diagnosis, and sensitivity, specificity, and accuracy were calculated. In addition, contrast-to-noise ratios were calculated. Image quality was significantly (P < 0.05) lower on the 3D FSE images than on the 2D FSE images [3D (i): 1.6 (SD, 0.43); 3D (ii): 2.35 (SD, 0.7); 3D (iii): 2.35 (SD, 0.5); 2D: 1.3 (SD, 0.35)]. No significant differences in diagnostic performance were found between 3D (i) and 2D FSE sequences. However, 16% fewer lesions were correctly detected with the 3D (ii) and (iii) sequences. Sensitivity was highest for the 2D sequence, and specificity was highest for the 3D (i) sequence. Confidence scores were higher for the 3D (i) sequence than for the 2D sequence. A significant increase (P < 0.05) in correctly measured cartilage lesions size and depth was found for the 3D (i) sequence over the standard 2D FSE sequence. Although the 3D FSE sequence performed better in depiction and characterization of cartilage abnormalities than the standard 2D FSE sequence, we currently do not recommend to use it as substitute. For the diagnosis of meniscal defects, however, no significant improvement was found.