Hong, Jin Ho
(Department of Radiology, Inha University Hospital, Inha University School of Medicine)
,
Lee, Ha Young
(Department of Radiology, Inha University Hospital, Inha University School of Medicine)
,
Kang, Young Hye
(Department of Radiology, Inha University Hospital, Inha University School of Medicine)
,
Lim, Myung Kwan
(Department of Radiology, Inha University Hospital, Inha University School of Medicine)
,
Kim, Yeo Ju
(Department of Radiology, Inha University Hospital, Inha University School of Medicine)
,
Cho, Soon Gu
(Department of Radiology, Inha University Hospital, Inha University School of Medicine)
,
Kim, Mi Young
(Department of Radiology, Inha University Hospital, Inha University School of Medicine)
Purpose: To quantitatively and qualitatively compare fat-suppressed MRI quality using iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) with that using frequency selective fat-suppression (FSFS) T2- and postcontrast T1-weighted fast spin-echo images of...
Purpose: To quantitatively and qualitatively compare fat-suppressed MRI quality using iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) with that using frequency selective fat-suppression (FSFS) T2- and postcontrast T1-weighted fast spin-echo images of the head and neck at 3T. Materials and Methods: The study was approved by our Institutional Review Board. Prospective MR image analysis was performed in 36 individuals at a single-center. Axial fat suppressed T2- and postcontrast T1-weighted images with IDEAL and FSFS were compared. Visual assessment was performed by two independent readers with respect to; 1) metallic artifacts around oral cavity, 2) susceptibility artifacts around upper airway, paranasal sinus, and head-neck junction, 3) homogeneity of fat suppression, 4) image sharpness, 5) tissue contrast of pathologies and lymph nodes. The signal-to-noise ratios (SNR) for each image sequence were assessed. Results: Both IDEAL fat suppressed T2- and T1-weighted images significantly reduced artifacts around airway, paranasal sinus, and head-neck junction, and significantly improved homogeneous fat suppression in compared to those using FSFS (P < 0.05 for all). IDEAL significantly decreased artifacts around oral cavity on T2-weighted images (P < 0.05, respectively) and improved sharpness, lesion-to-tissue, and lymph node-to-tissue contrast on T1-weighted images (P < 0.05 for all). The mean SNRs were significantly improved on both T1- and T2-weighted IDEAL images (P < 0.05 for all). Conclusion: IDEAL technique improves image quality in the head and neck by reducing artifacts with homogeneous fat suppression, while maintaining a high SNR.
Purpose: To quantitatively and qualitatively compare fat-suppressed MRI quality using iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) with that using frequency selective fat-suppression (FSFS) T2- and postcontrast T1-weighted fast spin-echo images of the head and neck at 3T. Materials and Methods: The study was approved by our Institutional Review Board. Prospective MR image analysis was performed in 36 individuals at a single-center. Axial fat suppressed T2- and postcontrast T1-weighted images with IDEAL and FSFS were compared. Visual assessment was performed by two independent readers with respect to; 1) metallic artifacts around oral cavity, 2) susceptibility artifacts around upper airway, paranasal sinus, and head-neck junction, 3) homogeneity of fat suppression, 4) image sharpness, 5) tissue contrast of pathologies and lymph nodes. The signal-to-noise ratios (SNR) for each image sequence were assessed. Results: Both IDEAL fat suppressed T2- and T1-weighted images significantly reduced artifacts around airway, paranasal sinus, and head-neck junction, and significantly improved homogeneous fat suppression in compared to those using FSFS (P < 0.05 for all). IDEAL significantly decreased artifacts around oral cavity on T2-weighted images (P < 0.05, respectively) and improved sharpness, lesion-to-tissue, and lymph node-to-tissue contrast on T1-weighted images (P < 0.05 for all). The mean SNRs were significantly improved on both T1- and T2-weighted IDEAL images (P < 0.05 for all). Conclusion: IDEAL technique improves image quality in the head and neck by reducing artifacts with homogeneous fat suppression, while maintaining a high SNR.
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제안 방법
The scanner was a gradient system with 44 mT/m maximum gradient field strength and a 200 T/m/s slew rate. Axial IDEAL T2-weighted FSE and postcontrast axial IDEAL T1-weighted FSE images were taken in addition to our conventional contrast enhanced neck MRI images, which consisted of axial, coronal, and sagittal precontrast T1-weighted FSE, axial and coronal T2-weighted FSE, axial FSFS T2-weighted FSE, coronal short inversion time inversion-recovery (STIR) images, postcontrast axial, coronal and sagittal FSFS T1-weighted FSE, and axial diffusion weighted images. Table 1 summarizes the imaging parameters used in the study sequences.
There are several limitations in the present study. First, the study cohort was relatively small, as the study was conducted as a preliminary study to evaluate the feasibility of the IDEAL technique in the head and neck. Second, it was not possible to regulate motion artifacts, including swallowing and breathing during scanning, to exclude them as causes of poor image quality, and many cases were excluded due to severe motion artifacts.
The images bearing the largest part of maxillary sinus, the crown of first lower molar tooth, the body of hyoid bone, and the base of arytenoid cartilage were selected to represent PNS, oral cavity, head-neck junction, and midneck levels, respectively. For each representative image, circular regions of interest (ROI) were manually located by an single investigator (J.H.H. with 3 years of experience in head and neck imaging) over medulla oblongata or cervical spinal cord. The ROIs were drawn as large as possible to include homogeneous areas of designated structures.
MR examinations were conducted using a 3-T MRI system (Discovery 750W; GE Healthcare, Milwaukee, WI, USA) with a Geometry embracing method (GEM) head and neck coil suite. The scanner was a gradient system with 44 mT/m maximum gradient field strength and a 200 T/m/s slew rate.
Comparison of artifacts around the PNS, and oral cavity was possible in 21, and 30 patients, respectively, because these areas were not included in the cranial scan range in other patients. Pathologic diagnoses of the patients were as follows; malignancy in the oral cavity (n = 11), oropharynx (7), salivary gland (4), larynx (3) and hypopharynx (3), metastatic cervical lymphadenopathy (2), lymphoma (1), and benign lesions including lymphangioma (1), paraganglioma (1), AVM (1), venous malformation (1), and soft tissue edema (1).
The degree of susceptibility artifacts with respect to signal loss and geographic distortion in three different sites of abrupt contour change or air-soft tissue interface were separately graded as follows: grade 1, excellent image quality without significant artifact; grade 2, minimal degree without significant image quality impairment; grade 3, moderate degree with image quality impairment, but preserved diagnostic reliability; grade 4, severe artifacts resulting in limited diagnostic reliability; and grade 5, severe artifacts resulting in non-diagnostic image quality.
대상 데이터
Sixty patients underwent the head and neck MR imaging during the period, and 24 patients were excluded due to severe motion artifacts. As a result, a total of 36 patients (23 men and 13 women; range, 24-85 years; mean, 55 years) were included in this study. Comparison of artifacts around the PNS, and oral cavity was possible in 21, and 30 patients, respectively, because these areas were not included in the cranial scan range in other patients.
데이터처리
Results of qualitative analyses of two image sets were compared using the two-sided Wilcoxon’s signed rank test for each individual reader.
0 (SPSS, Chicago, IL, USA). SNRs of IDEAL and FSFS sequences were compared by using the paired t-test. Results of qualitative analyses of two image sets were compared using the two-sided Wilcoxon’s signed rank test for each individual reader.
이론/모형
Calculation of the quantity of magnetic field inhomogeneity in each pixel from data is applied to generate the field map of IDEAL, by using asymmetric echoes to prevent fat-water “swapping”, which is frequently encountered using symmetric echoes, and by using the least-squares method.
Iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) technique using three asymmetric echo times and the three-point Dixon method for separating fat and water was introduced as an alternative solution for homogeneous fat suppression and reducing metal induced artifacts (4-14). Calculation of the quantity of magnetic field inhomogeneity in each pixel from data is applied to generate the field map of IDEAL, by using asymmetric echoes to prevent fat-water “swapping”, which is frequently encountered using symmetric echoes, and by using the least-squares method.
성능/효과
Both IDEAL FS T2- and postcontrast T1-weighted images scored significantly better for homogeneous fat suppression by both readers (P < 0.001 for both), and IDEAL significantly reduced the relative degrees of artifacts around the airway, PNS, and head-neck junction (P < 0.05 for all) both on T2- and T1-weighted images.
In conclusion, IDEAL FS T2- and postcontrast T1-weighted images improved image quality by reducing artifacts around the airway, PNS, and head-neck junction, while maintaining high SNR, and provided homogeneous fat suppression of the head and neck facilitating accurate diagnosis. IDEAL may be a useful fat suppression method for the head and neck region in general practice.
The SNRs of medulla oblongata in PNS level, and SNRs of cervical cord in oral cavity, head-neck junction and midneck level were significantly higher both on IDEAL T2- and postcontrast T1-weighted images than that of FSFS T2- and postcontrast T1-weighted images (P < 0.05 for all).
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