“Why is there such a radical difference between my chest X-ray and CT scan?”

CT is much better technology and can see way more

A CT scan uses multiple detectors and acquires cross-sectional imaging which gives 30 times better information as compared to a chest X-ray

The ct shows better definition of the lungs and pleura.

CT scan gives much more detailed anatomic information

The chest X-ray is the first line in diagnosis and it will provide a baseline to assess progression of disease or resolution as CT is expensive, uses contrast and results in excess radiation exposure if not used judiciously. Also, certain findings such as pneumothorax on a chest X-ray may obviate the need for CT.

Chest CT scan allows for a more detailed view compared to a chest X-ray. For example, a chest X-ray may identify an abnormality, but a chest CT scan should be able to show the exact location and examine the nature of a formation.
Chest X-ray provides a 2D image, while a chest CT scan is able to produce a 3D view of your organs.
An X-ray is built to examine dense tissues, while a CT scan is better able to capture bones, soft tissues and blood vessels all at the same time.
X-ray equipment is much smaller and less complex than a CT scan since a CT scanner needs to rotate around the patient being scanned.
Chest X-ray is a good low-cost, first-look exam. In order to move forward with your diagnosis and treatment, you might have to do a chest CT scan to have a better picture.

CT provides far greater information than chest X-ray.

A picture is worth a thousand words. You should Google chest CT and chest X-ray. You can see the difference. A chest X-ray projects radiation through your body to be captured by a film on the opposite side of your body. Whatever doesn’t make it, essentially leaves a shadow of your bones and organs. Some pathology can easily be demonstrated, some cannot.

A CT scan circles around your body and similarly captures the radiation that passes through, but it does so with greater capacity and detail. Allowing for more detailed imagery of the density of the different substances in your body. The “computed” part of “computed tomography” or “CT” computes or assembles the data collected into an image with greater detail than a single dimension chest X-ray. Also, the images acquired can be “windowed” to optimize the viewing of lung tissue, soft organs or bone to be more sensitive to pathology. The level of detail visible with a CT scan is much greater than that of a chest X-ray. Sometimes there is a hint of pathology on a chest X-ray that is better demonstrated on a more detailed CT scan. The reports for a CT will therefore be more detailed than for an X-ray since more of your body is demonstrated.

I hope that helps.