Have a 4mm non calcified nodule on lung.i have had 5 ct scans this year on my brain. would an mri or ultasound on lung be ok. worried about radiation?

Unfortunately, no...: The follow up evaluation of a pulmonary nodule as small as 4 mm requires requires extreme precision that is only possible from a repeat study of the same imaging modality (a second chest ct) as we are looking at potential change in size of only a millimeter or two. An ultrasound won't show pulmonary nodules and most chest mri's will not have the resolution to be very useful at this time.