• A novel technique has been proposed for dynamic MRI: Dynamic KWIC

1. Dynamic KWIC for Simultaneous High Spatial and High Temporal Resolution Imaging • A novel technique has been proposed for dynamic MRI: Dynamic KWIC • Permits image reconstruction at both high spatial and high temporal resolutions • Technique is based on an angle-interleaved projection reconstruction (PR) data acquisition and temporally selective data filtering • Effective temporal resolution is equal to a highly undersampled PR technique, but image quality similar to a fully sampled data set

2. • Rim enhancement • Spiculated/smooth • Focal/lobular Need for High Spatial and Temporal Resolutions High spatial resolution High temporal resolution

3. B C D A A D C k B y B D C A k x k D KWIC Data Acquisition and Reconstruction KWIC* = K-space Weighted Image Contrast Conventional projection reconstruction MRI acquires data that lie along radial lines in k-space (a). The inset figure shows the region surrounding the center of k-space. Within the k-space "pixel" (dashed box), there is a high degree of oversampling. (b) In KWIC, the central region of k-space is occupied only by select views of interest (e.g., a single echo time in radial FSE, or a narrow temporal window in dynamic imaging). The adjacent annular region(s) of k-space is occupied by adjacent echoes or adjacent time frame. * Song, et al. MRM 44:825-832 (2000).

4. In conventional DCE-MRI, long scan times are required to achieve high spatial resolution. Top: Four high resolution images, each requiring 2:00 acquisition time. Bottom: Dynamic KWIC images, where each high resolution data set was acquired in 8 underdsampled passes. The effective temporal resolution for each high-resolution image is 15 sec. Dynamic KWIC Image Acquisition & Reconstruction 512x384, 460µm Dynamic KWIC * Song, et al. MRM 52:815-824 (2004).

5. 15 sec/image; 512x48; 470µm 15 sec/image; 128x48; 1.9mm DCE-MRI with and without KWIC processing Low SNR Low spatial resolution Dynamic KWIC 15 sec/image; 470µm High SNR and high spatial resolution

6. Parametric Maps Pre-contrast Post-contrast Wash-out rate Peak enhancement Time to maximum slope

7. Conclusions • With angle-interleaved PR acquisition and temporally selective data filtering, both high temporal and high spatial resolutions can be achieved simultaneously. • The dynamic KWIC technique may be useful in various applications, including dynamic contrast-enhancement studies, hyperpolarized gas imaging, cardiac motion, and kinematic studies involving object motion.

8. Principal Component Analysis of Undersampled Radial Data Undersampled dynamic series PCA processed series Low SNR Streaks Higher SNR Reduced streaks PCA PCA can be used to analyze the dynamic time series of the undersampled radial data series. Components that primarily contribute to image streaking and noise are rejected, while those that contain information of the tumor are maintained.

9. Principal Component Analysis of Undersampled Radial Data a e c d b Figure 1 Results from PCA processing of undersampled radial data set (a) Full dataset image: 512 points x 384 views (2 min acquisition). (b) Magnified and cropped image of (a). (c) Image from a single pass: 512 points x 48 views (15 sec). (d) PCA processed: 512 points x 48 views (15 sec). (e) Parametric map: RED = Signal wash-out, BLUE = Plateau.