It sounds as if they are being very thorough, which is always a good thing. There are standard care pathways which use standard diagnostic tests. It's all routine, as they say on the best TV cop shows.
I'm not an expert but here's my simplified take on different scans (I'm hope someone who knows more about these things than I do will jump in and correct me if I get it wrong and I've added links to an NHS website which explains each of them). These are in ascending order of granularity/level of detail (and cost).
Ultrasound - uses high frequency soundwaves whose echoes are recorded and put on a screen. These are pretty good at spotting solid lumps like babies and some types of cancer, but there isn't much detail and the pictures can easily be obsured. In my case the ultrasound showed nothing, but I was told that this didn't mean that I was out of the woods.
Endoscopy - a lovely experience as you know. The camera goes down (or up if the problem is at "the other end") and you can see every bump, lump and scar as it progresses. Small pieces of tissue can be cut out for testing (biopsies) without the need to cut into the body. In my case the endoscopy showed a large lump that hadn't shown up on the ultrasound and the bipsies identified that it was cancer and what type of cancer it was.
X-rays - the good old-fashioned 2D representation. Sometimes a standard X-ray for something else will show an unexpected "shadow" which will lead to a referral for further tests and scans.
CT scan. A high number of salami slice X rays are taken of your body. These have enough detail to show exactly where a cancer is, whether it has spread elsewhere and, by comparing with earlier scans, any changes in size.
MRI scans - you lie in a strong magnetic field and radio-frequency waves are directed at your body. This produces highly detailed 3 D images of your body. MRI scans are often used to plan any physical surgical work.
PET scans - a special chemical is injected and the PET scan shows how this has built up - an indication of how well different organs are functioning. PET scans are often used with either CT or MRI scans to give the team with a really good view of what is happening.
I hope this helps!