T1 Quantification of the Cortical Bone Employing Short-TE MRI at 1.5 and 3 Tesla
A, Abbasi Rad
S, Shojaie Moghadam
M, Saligheh Rad
H. T1 Quantification of the Cortical Bone Employing Short-TE MRI at 1.5 and 3 Tesla,
Iran J Radiol.
Online ahead of Print
; 11(30th Iranian Congress of Radiology):e21303.
Larger pores in human cortical bone (> 30 m) have essential role in its mechanical competence, suggesting to quantify such proton pools as a reliable measure of cortical bone porosity and thus, cortical bone quality. Signal from such pores can be captured using short echo time (STE) pulse sequence with echo-time in the range of 0.51 ms. Since T1-relaxation increases with the porosity volume; in the first step we have quantified T1 values as a reliable measure of cortical porosity employing the dual-TR technique.
Results show that the T1 values quantified by this method are accurately close to the ones reported in the ultra-short echo time (UTE) literature. Such T1 values can be used in the quantification process of cortical bone porosity to discriminate osteoporotic bone from normal.
Patients and Methods:
Image Acquisition: Mid-tibia images were acquired using STE pulse sequence with two different TR values (TR1 = 20 ms and TR2 = 60 ms) on both 1.5T (Siemens, Magnetom Avanto 18 channel) and 3T (Siemens Tim Trio, Erlangen, Germany) MR scanners. Volunteers enrolled into our study were 3 males and 5 females (20-57 years with the mean age of 37.4) for 1.5T acquisition, and 2 males and 3 females (26-37 years with the mean age of 29) for 3T acquisition. An 8-channel Tx/Rx knee coil was used for both acquisitions. T1-Quantification: Steps of quantification are as follows: (1) manual segmentation of the whole cortical bone at each of the two images with different TRs; (2) computation of the ratio value, by dividing the mean signal intensities of the segmented cortical bone acquired from long-TR (TR2) and short-TR (TR1) images, respectively; (3) calculation of cortical bone T1-value at each imaging slice; and (4) calculation of the average T1-values for each subject from ten different slices. Evaluation of signal-to-noise ratio (SNR): To evaluate SNR values, we placed two ROIs on each acquired image. The first ROI was on the segmented cortical bone and the second one on the background noise. Then, we calculated SNR by dividing the mean intensity of the first ROI by the mean intensity of the second one. This evaluation was performed on images with higher intensity (TR = 60). The obtained SNR values were in acceptable range (SNR > 12 at 1.5 T and SNR > 17 at 3 T).
Results for quantitative measurement of T1-values were shown in eight and five healthy volunteers using STE pulse sequence at 1.5 and 3 T respectively. Measurements were performed for both genders, resulting in the mean T1-values of about 202.81 ms and 238.56 ms for human cortical pore water at 1.5T and 3 T respectively. Such T1 quantities are in a good agreement with the values reported in the UTE literature (380-775 ms and 200-400 ms at 4.7T and 3T, respectively).
Results show that quantifying T1-relaxivity of the cortical bone using STE-MRI is feasible with the similar accuracy of UTE imaging. Such pulse sequences are available on commercial MRI magnets in everyday clinics, save money and time to half of what UTE needs; meaning that STE pulse sequence can be utilized as a proper alternative in quantifying cortical bone parameters in-vivo.
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