We present X-ray dust scattering halo results based on our 76 ks Chandra  ACIS-S/HETGS observation of the LMXB dipping source 4U 1624-490 .
Through analysis of the halo light curves with 2-6Â keV spectra over the persistent and dipping periods , we estimate a geometric distance of \sim 15Â kpc to 4UÂ 1624-490 .
We also fit halo radial profiles with different ISM dust grain models to assess the location , uniformity , and density of the halo .
Our analysis shows that the dust spatial distribution is not uniform along the line-of-sight ; rather , it is consistent with the spiral arm structure mapped in Hii .
The large difference between the absorption Hydrogen column ( N _ { H } ^ { abs } \sim 8 \times 10 ^ { 22 } cm ^ { -2 } ; probes all gas along the line-of-sight ) derived from broadband spectral fitting , and the scattering Hydrogen column ( N _ { H } ^ { sca } \sim 4 \times 10 ^ { 22 } cm ^ { -2 } ; probes only Galactic gas ) derived from our studies of the 4UÂ 1624-490 X-ray halo suggests that a large fraction of the column is local to the X-ray binary .
We also present ( and apply ) a new method for assessing the Chandra  point spread function at large ( > 50 ^ { \prime \prime } ) angles , through use of the time delays from the observed dips .