The medical technologies used for guidance are most commonly fluoroscopy (image intensification), which is the use of continuous low energy x-rays so your procedure is guided by continuous real-time screening to ensure that the needles or probes go right to the target first time, and CT, which is a high precision but iterative technique which shows cross sections of the part being imaged but which cannot easily be used to show realtime moving images and can also be associated with high x-ray exposure.
The other commonly used imaging modality is ultrasound, which is a completely safe technology where very high frequency sound waves are passed through the body. Like CT, these show cross sectional images of the body but as ultrasound is used continuously it can be used to build up a three dimensional dynamic picture of the part being studied, so we can see that body part in motion and if pressure is applied to it. Ultrasound guidance is commonly used for procedures into soft tissue, such as muscles, joints or nerves, but it cannot be used for procedures where the target is in or sheltered by bone as ultrasound sound waves simply reflect off bone.
The substances injected are typically steroids, Hyaluronic acid, solutions for joint lubrication, local anaesthetic and Botulinum toxin (Botox®). Each of these is used for specific reasons but the most commonly injected substances are steroids, which can be very effective in the management of spinal, joint or nerve problems.