Do ultrasound measurements correlate with CT and MRI?

I found an interesting article the other day which talked about correlating ultrasound measurements of kidney tumors with CT and MRI measurements.  When I thought about it, it made sense to do this study.  If ultrasound measurements correlate well with these other modalities, why not use ultrasound to monitor the effects of chemotherapy on kidney tumors and other masses.  Ultrasound costs much less, and does not use ionizing radiation.  Why not use ultrasound on all sonographically visible tumors to monitor the effects of therapy?

Objective

To evaluate whether ultrasonography was inferior in detecting the size of a renal mass preoperatively because of the increased attention on the harmful effects of ionizing radiation in medical imaging.

http://www.goldjournal.net/article/S0090-4295%2811%2902465-4/abstract