Edmond A Knopp — Page 2

PubMedDate not supplied

Three-dimensional, T1-weighted gradient-echo imaging of the brain with a volumetric interpolated examination.

BACKGROUND AND PURPOSE: T1-weighted, 3D gradient-echo MR sequences can be optimized for rapid acquisition and improved resolution through asymmetric k-space sampling and interpolation. We compared a volumetric interpolated brain examination (VIBE) sequence with a magnetization-prepared rapid acquisition gradient echo (MP RAGE) sequence and a 2D T1-weighted spin-echo (SE) sequence. METHODS: Thirty consecutive patients known or suspected to have focal brain lesions underwent postcontrast studies (20 mL of gadopentetate dimeglumine) with VIBE, MP RAGE, and 2D T1-weighted SE imaging. Source and 5-mm VIBE and MP RAGE reformations, and 5-mm T1-weighted SE images were compared qualitatively and by using signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR). SNRs in a gadolinium-doped water phantom were also measured for all three sequences. RESULTS: On the source images, SNRs for gray matter (GM) and white matter (WM), and CNRs for WM-to-GM and contrast-enhancing lesion-to-GM were slightly, but significantly higher for the VIBE sequence than for the MP RAGE sequence (P <.05). On 5-mm reformations, WM-to-GM CNR was significantly higher on VIBE and MP RAGE images than on T1-weighted SE images (P <.001), but contrast-enhancing lesion-to-GM CNRs were higher on SE images compared with both gradient-echo sequences (P <.001). Qualitatively, VIBE images showed fewer flow artifacts than did SE and MP RAGE images (P <.05). In the phantom, VIBE SNR was higher than MP RAGE SNR for short T1 relaxation times. CONCLUSION: VIBE provides an effective, alternative approach to MP RAGE for fast 3D T1-weighted imaging of the brain.

Adult↗

PubMedDate not supplied

Glioma grading: sensitivity, specificity, and predictive values of perfusion MR imaging and proton MR spectroscopic imaging compared with conventional MR imaging.

BACKGROUND AND PURPOSE: Sensitivity, positive predictive value (PPV), and negative predictive value (NPV) of conventional MR imaging in predicting glioma grade are not high. Relative cerebral blood volume (rCBV) measurements derived from perfusion MR imaging and metabolite ratios from proton MR spectroscopy are useful in predicting glioma grade. We evaluated the sensitivity, specificity, PPV, and NPV of perfusion MR imaging and MR spectroscopy compared with conventional MR imaging in grading primary gliomas. METHODS: One hundred sixty patients with a primary cerebral glioma underwent conventional MR imaging, dynamic contrast-enhanced T2*-weighted perfusion MR imaging, and proton MR spectroscopy. Gliomas were graded as low or high based on conventional MR imaging findings. The rCBV measurements were obtained from regions of maximum perfusion. Metabolite ratios (choline [Cho]/creatine [Cr], Cho/N-acetylaspartate [NAA], and NAA/Cr) were measured at a TE of 144 ms. Tumor grade determined with the three methods was then compared with that from histopathologic grading. Logistic regression and receiver operating characteristic analyses were performed to determine optimum thresholds for tumor grading. Sensitivity, specificity, PPV, and NPV for identifying high-grade gliomas were also calculated. RESULTS: Sensitivity, specificity, PPV, and NPV for determining a high-grade glioma with conventional MR imaging were 72.5%, 65.0%, 86.1%, and 44.1%, respectively. Statistical analysis demonstrated a threshold value of 1.75 for rCBV to provide sensitivity, specificity, PPV, and NPV of 95.0%, 57.5%, 87.0%, and 79.3%, respectively. Threshold values of 1.08 and 1.56 for Cho/Cr and 0.75 and 1.60 for Cho/NAA provided the minimum C2 and C1 errors, respectively, for determining a high-grade glioma. The combination of rCBV, Cho/Cr, and Cho/NAA resulted in sensitivity, specificity, PPV, and NPV of 93.3%, 60.0%, 87.5%, and 75.0%, respectively. Significant differences were noted in the rCBV and Cho/Cr, Cho/NAA, and NAA/Cr ratios between low- and high-grade gliomas (P <.0001,.0121,.001, and.0038, respectively). CONCLUSION: The rCBV measurements and metabolite ratios both individually and in combination can increase the sensitivity and PPV when compared with conventional MR imaging alone in determining glioma grade. The rCBV measurements had the most superior diagnostic performance (either with or without metabolite ratios) in predicting glioma grade. Threshold values can be used in a clinical setting to evaluate tumors preoperatively for histologic grade and provide a means for guiding treatment and predicting postoperative patient outcome.

Adolescent↗