Your dentist or implant surgeon will take x-rays of your jaw, paying special attention to the area which will be treated. A general review of these x-rays will allow the dentist to carefully inspect for any additional teeth or areas in the bone that require treatment (whether for implants or otherwise). Many dentists will use a panoramic radiograph, which shows all of the upper and lower jaws' bones and teeth, to diagnose other dental and bone pathology. These can also be used to assess the height of available bone and the relation and position of other anatomic structures - all considered as part of the overall analysis for implants.
The most accurate form of x-ray imaging currently available is the CT scan, commonly known as a CAT scan. Medical CT scanners are often used by dentists to diagnose, analyze and devise treatment plans for implant surgery so you may be referred to a radiologist during the diagnosis process.
There are other types of CT scanners known as Cone Beam CT scanners (CBCT) that can provide similar images and can be converted to the many commonly used software programs available for analysis by your dentists. CBCT scanners use significantly less radiation and may be available to you at an imaging center or in your surgeon's office. Both types of CT scanners provide very detailed, three-dimensional images that can accurately measure the height and width of available bone, as well as locate the nearby anatomic structures (such as the maxillary sinuses and mandibular nerves) that the surgeon must be mindful of during surgery.
Because all radiation dosages are cumulative, and the potentially harmful effects of excessive radiation are well documented, the benefits of improved diagnostic imaging must be weighed against the risks of radiation exposure for your particular needs and circumstances.