Doctors seeking to offer faster, more helpful, even life-saving diagnoses for their Medicare patients – while, at the same time increasing their own revenue stream – have started installing testing equipment in their offices.The Wall Street Journal reports that in Medicare alone, payments to physicians for 4 of the top 10 fastest growing services rose by $123.5 million to $135 million between 2012 and 2014. Each of the 4 services is designed to diagnose or treat specific conditions.Related: FIVE FAV PHARMAS UNDER FIVEElectronic BrachytherapyElectronic brachytherapy, or EBT, uses X-ray energy to treat certain cancers. Originally it was thought these devices would be used to provide breast cancer treatment, a complicated procedure, making Medicare reimbursement fairly high.Dermatologists, however, soon discovered the machines could also be used on some types of nonmelanoma skin cancer. Although doctors who use the machines have to pay oncologists to use them the procedures are lucrative.Sweat TestingOne unusual neurological condition can be diagnosed through something called sweat testing. The device used, in a doctor’s office, tests whether patients sweat in response to low-voltage current. The test measures possible nerve damage.Doctors defend the expensive tests, saying the results motivate patients to change lifestyle to deal with the condition they have – often related to diabetes. Some neurologists, however, say there is no clear evidence the new test improves on older methods.Tear OsmolarityAnother test measures the saltiness of tears and is known as tear osmolarity. In 2012, a device was introduced that doctors could use in their offices to conduct the test. Coincidentally physicians could bill Medicare separately for the test.Tear osmolarity is used to diagnose dry eyes and is used primarily by ophthalmologists and optometrists. In 2014 doctors received $14.8 million in payments. In 2013 they received just $1.75 million.ElectroretinographyElectroretinography (ERG) is an eye test used to detect abnormal function of the retina. During the test the light-sensitive cells of the eye – rods and cones, and connecting cells in the retina – are examined.The test looks for a number of conditions including retinitis pigmentosa, hereditary retinal degeneration and a condition known as cone dystrophy.Related: BAYER OFFERS MONSANTO $65 BILLION WORTH OF ASPIRINStocks To ConsiderAmong the companies that market devices designed to provide the services listed above are four in the public sector.TearLab Corp (NASDAQ:TEARC)TearLab Corporation has commercialized a proprietary in vitro diagnostic tear testing platform popular with eye care professionals. The platform was designed to be used at point-of-care (doctor’s office).IsoRay Inc. (AMEX:ISRB)IsoRay, Inc. develops, manufactures and sells isotope-based medical products and devices for the treatment of cancer and other malignant diseases. The company’s equipment is cleared to treat solid tumors using Cesium-131.Endologix Inc. (NASDAQ:ELGXC)Endologix, Inc. manufactures and markets products for the treatment of coronary and vascular diseases. The company is considered a leader in the field of vascular brachytherapy.Icad Inc. (NASDAQ:ICADB)Icad, Inc. manufactures digital image scanners, densitometers, film digitizers and related software for applications in medical imaging and life sciences.