Is a CT scan better at detecting blood clots in the veins/lungs/body versus ultrasounds?

Depends on site. Ct is the gold standard for detecting clots in the lungs (pulmonary embolism). Ultrasound is more reliable for detecting clots in the veins of the arms or legs. Clots in the neck veins are usually seen with ultrasound, while clots in the brain usually need an MRI for diagnosis.