Manabu Arai^{1}, Koichi Oshio^{1}, Shigeo Okuda^{1}, and Masahiro Jinzaki^{1}

Weighted diffusion subtraction (WDS) is a new imaging tool which may be useful for estimating the tissue characteristics within a voxel. In this study, DWI histogram (low b vs. high b) was generated and referred to WDS. On the histogram, the data distribution represents the tissue composition with blurring caused by partial volume. DWI histogram can visualize the relationship between T2WI (low b value DWI) and WDS.

**Subjects**: Synovial sarcoma and endometrial cancer (4 cases respectively) were examined. The pathology of each case was proven on the specimen resected in the operation.

**Data Acquisition**: MR images were acquired on a 1.5T scanner (Signa HD, GE Healthcare, Waukesha, WI, USA) using body coil, quadrature foot coil as a receiver. Following routine MRI including T1WI and T2WI, EPI-based DWI (b = 0 and 1000 s/mm^{2}) was obtained with following parameters:TR/TE, 4200-5000/77-82 ms; slice thickness/spacing, 5-7/7-11 mm; matrices 128x160 or 96x128. The pixel size was ranged between 0.7 mm and 1.6 mm, depending the diameter of the subject.

**WDS and Histogram Calculation**:

WDS is a subtraction technique, using a pixel-by-pixel calculation:

$$S(x, y) = S_0(x, y) \exp(- \Delta b D_{thres}) - S_1(x, y) \\ = S_0(x, y) \exp(- \Delta b D_{thres}) - S_0(x, y) \exp(- \Delta b ADC(x, y)), $$

where *S* is the signal intensity of WDS, *S _{0}* is that of the image obtained with the low b value, and

The distribution of data points on DWI histogram is estimated to be dependent on tissue component, and the spread of the distribution is considered to reflect partial volume effect. The shape of the distribution varies depending on the disease and the scanning area, but the distribution of the tumor on DWI histogram can be discriminated to some extent.

The voxels corresponding
to data points plotted above the line of
slope 1 are demonstrated as hypointense area in WDS images
for each *D _{thres}* setting. The
signal intensity of WDS is proportional to the difference between point A and B (Fig.4). Therefore, DWI histogram can also show the relationship between T2WI (low
b value DWI) and WDS.

1. Oshio K, Okuda S, Shinmoto H. Removing Ambiguity Caused by T2 Shine-through using Weighted Diffusion Subtraction (WDS). Magn Reson Med Sci. 2016;15(1):146-8.

2. Manabu Arai, Shigeo Okuda, Sota Oguro, Kuniaki Ohori, Koichi Oshio. Application of Weighted Diffusion Subtraction (WDS) to Synovial Sarcomas: Possibility of Visualising Tumor Cellularity. Proc ISMRM 2017, p1808.