Answer to Question 1
Each test has its place and usefulness. For getting a fast, less expensive screening of organs, ultrasound is best. If time is not a major factor and/or a more detailed test is required, the more expensive CT scan can be completed. The patient has to be brought to the CT scanner while ultrasound can be brought to the patient, so mobility is also a factor.
DEXA would be used for the most accurate and detailed study of bone density and body fat percentage.
Answer to Question 2
According to NCHS Percentiles, he should weigh about 70 lbs and be about 54 tall.