Richard Znamirowski

Ultrashort Echo Time MR Imaging of Osteochondral Junction of the Knee at 3 T: Identification of Anatomic Structures Contributing to Signal Intensity

PURPOSE To image cartilage-bone interfaces in naturally occurring and experimentally prepared human cartilage-bone specimens at 3 T by using ultrashort echo time (TE) (UTE) and conventional pulse sequences to (a) determine the appearance of the signal intensity patterns and (b) identify the structures contributing to signal intensity on the UTE MR images. MATERIALS AND METHODS This study was exempted by the institutional review board, and informed consent was not required. Five cadaveric (mean age, 86 years +/- 4) patellae were imaged by using proton density-weighted fat-suppressed (repetition time msec/TE msec, 2300/34), T1-weighted (700/10), and UTE (300/0.008, 6.6, with or without dual-inversion preparations at inversion time 1 = 135 msec and inversion time 2 = 95 msec) sequences. The UTE images were compared with proton density-weighted fat-suppressed and T1-weighted images and were evaluated by two radiologists. To identify the sources of signal on the UTE images, samples including specific combinations of tissues (uncalcified cartilage [UCC] only, calcified cartilage [CC] and subchondral bone [bone] [CC/bone], bone only; and UCC, CC, and bone [UCC/CC/bone]) were prepared and imaged by using the UTE sequence. RESULTS On the UTE MR images, all patellar sections exhibited a high-intensity linear signal near the osteochondral junction, which was not visible on protein density-weighted fat-suppressed or T1-weighted images. In some sections, focal regions of thickened or diminished signal intensity were also found. In the prepared samples, UCC only, CC/bone, and UCC/CC/bone samples exhibited high signal intensity on the UTE images, whereas bone-only samples did not. CONCLUSION These results show that the high signal intensity on UTE images of human articular joints originates from the CC and the deepest layer of the UCC, without a definite contribution from subchondral bone. UTE sequences may provide a way of evaluating abnormalities at or near the osteochondral junction. (c) RSNA, 2010.

Magic angle effect in magnetic resonance imaging of the Achilles tendon and enthesis.

Collagen fibers in tendons and entheses are highly ordered. The protons within the bound water are subject to dipolar interactions whose strength depends on the orientation of the fibers to the static magnetic field B(0). Clinical pulse sequences have been employed to investigate this magic angle effect of the Achilles tendon, but only limited to imaging appearance with a signal void at many angular orientations due to its short T2. Here we investigated the magic angle effect of the Achilles tendons and entheses on a clinical 3-T scanner using clinical sequences as well as an ultrashort TE sequence with a minimal TE of 8 micros. Qualitative and quantitative investigation of the angular-dependent imaging appearance, T1 and T2* values were performed on five ankle specimens. There was a significant increase in signal intensity for all pulse sequences near the magic angle. Mean T2* for tendon increased from 1.94+/-0.28 ms at 0 degrees relative to the B(0) field to 15.25+/-2.13 ms at 55 degrees, and mean T1 increased from 598+/-37 ms at 0 degrees to 621+/-44 ms at 55 degrees. There was less magic angle effect for enthesis whose mean T2* increased from 4.12+/-0.37 ms at 0 degrees to 12.46+/-1.78 ms at 55 degrees, and mean T1 increased from 685+/-41 ms at 0 degrees to 718+/-56 ms at 55 degrees.

Assessment of cortical bone with clinical and ultrashort echo time sequences

We describe the use of ultrashort echo time (UTE) sequences and fast spin echo sequences to assess cortical bone using a clinical 3T scanner. Regular two‐ and three‐dimensional UTE sequences were used to image both bound and free water in cortical bone. Adiabatic inversion recovery prepared UTE sequences were used to image water bound to the organic matrix. Two‐dimensional fast spin echo sequences were used to image free water. Regular UTE sequences were used together with bicomponent analysis to measure T*2s and relative fractions of bound and free water components in cortical bone. Inversion recovery prepared UTE sequences were used to measure the T*2 of bound water. Saturation recovery UTE sequences were used to measure the T1 of bone water. Eight cadaveric human cortical bone samples and a lower leg specimen were studied. Preliminary results show two distinct components in UTE detected signal decay, a single component in inversion recovery prepared UTE detected signal decay, and a single component in saturation recovery UTE detected signal recovery. Regular UTE sequences appear to depict both bound and free water in cortical bone. Inversion recovery prepared UTE sequences appear to depict water bound to the organic matrix. Two‐dimensional fast spin echo sequences appear to depict bone structure corresponding to free water in large pores. Magn Reson Med 70:697–704, 2013.

Direct imaging and quantification of carotid plaque calcification

Carotid plaque calcification normally appears as a signal void with clinical MR sequences. Here, we describe the use of an adiabatic inversion recovery prepared two‐dimensional ultrashort echo time sequence to image and characterize carotid plaque calcification using a clinical 3‐T scanner. T1, T  2* , and free water content were measured for seven carotid samples, and the results were compared with micro‐CT imaging. Conventional gradient echo and fast spin echo images were also acquired for comparison. Correlations between T1, T  2* , free water concentration, and mineral density were performed. There was a close correspondence between inversion recovery prepared two‐dimensional ultrashort echo time morphologic and micro‐CT appearances. Carotid plaque calcification varied significantly from sample to sample, with T1s ranging from 94 ± 19 to 328 ± 21 msec, T  2* s ranging from 0.31 ± 0.12 to 2.15 ± 0.25 msec, and free water concentration ranging from 5.7 ± 2.3% to 16.8 ± 3.4%. There was a significant positive correlation between T1 (R = 0.709; P < 0.074), T  2* (R = 0.816; P < 0.025), and free water concentration, a negative correlation between T1 (R = 0.773; P < 0.042), T  2* (R = 0.948; P < 0.001) and CT measured mineral density, and a negative correlation between free water concentration (R = 0.936; P < 0.002) and mineral density. Magn Reson Med, 2010.

Ultrashort te t1ρ magic angle imaging

An ultrashort TE T1ρ sequence was used to measure T1ρ of the goat posterior cruciate ligament (n = 1) and human Achilles tendon specimens (n = 6) at a series of angles relative to the B0 field and spin‐lock field strengths to investigate the contribution of dipole–dipole interaction to T1ρ relaxation. Preliminary results showed a significant magic angle effect. T1ρ of the posterior cruciate ligament increased from 6.9 ± 1.3 ms at 0° to 36 ± 5 ms at 55° and then gradually reduced to 12 ± 3 ms at 90°. Mean T1ρ of the Achilles tendon increased from 5.5 ± 2.2 ms at 0° to 40 ± 5 ms at 55°. T1ρ dispersion study showed a significant T1ρ increase from 2.3 ± 0.9 ms to 11 ± 3 ms at 0° as the spin‐lock field strength increased from 150 Hz to 1 kHz, and from 30 ± 3 ms to 42 ± 4 ms at 55° as the spin‐lock field strength increased from 100 to 500 Hz. These results suggest that dipolar interaction is the dominant T1ρ relaxation mechanism in tendons and ligaments. Magn Reson Med, 2013.

Optimizing MR signal contrast of the temporomandibular joint disk.

To use a tissue specific algorithm to numerically optimize UTE sequence parameters to maximize contrast within temporomandibular joint (TMJ) donor tissue.

Ultrashort echo time T1ρ is sensitive to enzymatic degeneration of human menisci

Objective The aim of the study was to determine whether quantitative ultrashort echo time (UTE) -T1&rgr; magnetic resonance (MR) measurements are sensitive to proteoglycan degradation in human menisci by trypsin digestion. Methods Conventional and quantitative UTE-T1&rgr; MR sequences were performed on 4 meniscal samples using a 3T scanner. Magnetic resonance imaging was performed before and after 4, 8, and 12 hours of trypsin solution immersion, inducing proteoglycan loss. One sample was used as a control. Digest solutions were analyzed for glycosaminoglycan (GAG) content. The UTE-T1&rgr; studies were analyzed for quantitative changes. Results Images showed progressive tissue swelling, fiber disorganization, and increase in signal intensity after GAG depletion. The UTE-T1&rgr; values tended to increase with time after trypsin treatment (P = 0.06). Cumulative GAG loss into the bath showed a trend of increased values for trypsin-treated samples (P = 0.1). Conclusions Ultrashort echo time T1&rgr; measurements can noninvasively detect and quantify severity of meniscal degeneration, which has been correlated with progression of osteoarthritis.