More important than high volume go to a place with high diversity of cases. That is equal to a tertiary referral center with sub-specialties in almost all fields.
High volume can help keeping up with the speed. IMO, it is a skill that can be obtained pretty fast in the first year of your pp. But the diversity of cases you have seen and esp subspecialty read with attending can not be obtained with pp.
High volume should not be a major factor for choosing a residency. On the other hand a place with low volume is a Red flag. Ask residents about their daily working hours, call and about how busy they are during a call. That shows a lot.
Be careful. Most senior residents over-estimate the number of studies they read. Also it has become a subject to brag about.
Recommendations:
1- Make sure the place has sub-specialist attending in all fields of radiology on a daily basis including chest, cardiac, Nucs and Mammo. Almost every place has Neuro, MSK, Body and IR people.
2- Make sure as a resident you get dedicated rotations in Body MR, Brain MR and MSK MR.
3- Make sure the hospital has strong sub-specialty groups including ENT, Neurology, Ortho, GI, Liver, Nephro and ...
4- High volume is not as important. As busy chest rotation may all be chest X-rays and CTs versus a rotation composed of Chest X-ray, Chest CT, HRCT chest, Cardiac CT and MR.
5- For X-ray there is more than enough in every program. Probably an average of 20-25 CTs per day work is the minimum requirement. For call, 60-80 studies composed of half X-rays and the rest cross sectional is the minimum. Also dedicated rotations in Neuro, MSK and body MR each at least a total of 2 months with at least daily 10-15 Brain MR in neuro, 5-10 MSK MR and 3-4 Body MR during each month of rotation is needed. If the numbers are less than these, the education is probably sub-optimal. On the other hand, don't be picky about the exact numbers.