How big is a mammo study?
It depends. I was recently asked what is the average size of a mammography study. I asked for clarification, what do you mean? I received a somewhat strange look and the response mammography, you know breast imaging….
Bottom line up front, somewhere between 20 MB and 1GB per exam
The problem is that there is no easy answer to that question because well, it depends. For starters there is as we all know a huge difference between tomography and plain film mammo. So averaging the two would vary greatly depending on the ratio of tomo to mammo. If you look in your VNA they will often share the modality code MG so how do you tell the difference? Number of images? You could assume that anything over 10 images is tomo. Ok so the next way to tell would be to get into your database and do a query for the SOP Class Breast Tomosysnthesis Image Storage (1.2.840.10008.5.1.4.126.96.36.199.3) however, you will find that within a study you will have a few tomo images and plan mammo images stored. Then again, you may be working with a popular vendor who stores the tomo images in a proprietary and much small format using the secondary capture SOP class (1.2.840.10008.5.1.4.1.1.7) easy right? All you need to do is isolate out the 2D exams from the exams containing a 3D image, then find out if you are using the BTO SOP class or the secondary capture SOP, THEN you can average your exams and get the average study size, right? Well sort of..
NOW we need to determine if they are compressed or not. To figure that out you need to look at the transfer syntax. Many modalities will default to Implicit VR Endian, which is transfer syntax (1.2.840.10008.1.2) this is uncompressed. Many PACS will take the syntax that the modality sent and refuse to change it for fear of impacting image quality. Therefore, the study is stored on disk and in the long-term archive or VNA in the same format. Unless you get into inbound and outbound compression which is a whole different topic. There are of course many different transfer syntaxes with varying compression, but we will take the other common one, JPG 2000 lossless (1.2.840.10008.1.2.4.90). Either compression can be applied to any of the SOP classes described above.
So, the question stands, what type of mammo do you mean? Standard format or proprietary (but very common) and compressed or uncompressed. How you ask the question will skew the answer dramatically. Given the trend in the market tomo is growing so the average in Dec 2017 is very different than the average in Dec 2016.
If you have read all the way through this, the breast tomo format lossless compressed averaged out to be 711 MB, while the secondary capture format also lossless compressed averaged in at 194 MB.
Please let me know what topics you would like to discuss