A Thallium Stress test looks at the blood flow to your heart muscle at rest and during stress. During a stress test, a radioactive material called Thallium is injected into a vein. A gamma camera takes pictures of the Thallium in your heart. the EKG and Echo were at rest and they are Fine !
now A Thallium Stress test just to see how your heart Managing the blood during stress.
No, the work out on the slope, has nothing to do with your present problem.
Because the stress test was positive, that indicates that your heart is suffering ischemia under certain stress conditions.
The most logical way to proceed (in MHO) should it be by making a catheterism to see the state of your coronaries and, in the same intervention, place stents if they are necessary.
With the thallium test, most probably, he will see areas of the muscle of your heart that do not receive blood enough, this is why you have the pain, and therefore he will prescribe the catheter afterwards anyway.
Of course in the catheterism you also receive a variable dose of radiation, proportional to the duration of it, due to the fluorescence used to visualize the procedure.