It is now possible to examine how the brain looks, functions and gets its blood supply. These tests can outline the affected part of the brain and help define the problem created by stroke. Most of these tests are safe, painless and can be done as an outpatient. A doctor must decide on a case-by-case basis whether such tests will be useful, and if so, which ones to use.

Some of the Tests useful in the investigation of Stroke

Computerized axial tomographic scan (C.T. or CAT scan)
Magnetic resonance imaging scanning (M.R.I.)
Radionuclide angiography
Electroencephalogram (E.E.G.)
Evoked response test
Doppler ultrasound test
Carotid phonoangiography
Digital subtraction angiography (D.S.A.)

• Computerized axial tomographic scan (C.T. or CAT scan) - Imaging procedure that uses x-rays to generate an image of the brain. Doctors use CT to determine whether a stroke has occurred and to identify the type of stroke: ischemic (result of blockage) or hemorrhagic (result of bleeding).
• Magnetic resonance imaging scanning (M.R.I.) - In this imaging procedure, the patient is placed in a magnetic field, causing a change in the behavior of the cells in the brain. Once the patient is in a magnetic field, the head is subjected to bursts of energy of a known frequency. The response of the brain cells to these bursts of energy is detected in the form of signals that ultimately generate the image of the brain. MRI can provide very accurate images of the brain and is used to determine the presence, location and size of aneurysms and arteriovenous malformations, which are potential sources for hemorrhagic stroke.
• Radionuclide angiography - An imaging procedure where radioactive compounds are injected into a vein in the arm and allowed to be carried in the bloodstream toward the head. As the radioactive compound circulates in the bloodstream, it is constantly emitting bursts of radiation. Once the radioactive compound reaches the brain, these bursts of radiation are detected by a special detector and used to form an image of the brain. This imaging procedure can detect blocked blood vessels and areas where the brain has been deprived of blood flow and is damaged.

• Electroencephalogram (E.E.G.) - In this diagnostic procedure, small metal disks (electrodes) are placed at strategic locations on a person's scalp. The electrodes can detect the electrical activity in the form of impulses that are then transcribed to paper. By observing the characteristics of the impulses such as intensity (how large in the impulse), duration (how wide is the impulse), frequency (how often do impulses occur during a given time) and location (what region of the brain is producing these impulses), an EEG can provide valuable information about underlying problems in the brain.
• Evoked response test - A diagnostic procedure that provides a measurement of the brain's ability to process and react to different sensory stimuli. A doctor evokes a visual response by flashing a light or checkerboard pattern in front of a patient. For auditory evoked responses, a doctor produces a sound in one of the patient's ears. For bodily evoked responses, one of the nerves in an arm or leg is electrically stimulated. The responses from either of these sensory stimuli can indicate abnormal areas of the brain.

• Doppler ultrasound test - In this imaging procedure, ultrasound or high-frequency sound waves are used to detect blockages in the carotid artery . A Doppler probe or instrument capable of generating ultrasound waves is placed on the neck, very close to the carotid artery. Ultrasound waves generated from the probe travels through the neck and bounces off the moving blood cells. The reflected sound wave, now returning to the probe at a different frequency, is then detected by the same probe. The change in frequency of the sound waves is related to the speed of the blood cells and hence the blood flow.
• Carotid phonoangiography - In this diagnostic procedure, a sensitive microphone is placed on the neck, very close to the carotid artery, to record generated sounds. Ordinarily, in a normal artery, blood flows in a smooth and controlled manner. However, the presence of blockages, such as those caused by atherosclerosis, disrupt the controlled nature of blood flow, causing the blood flow to become turbulent. The turbulent blood flow can create a sound, called a bruit , that can be detected and registered by the microphone. The presence of a bruit indicates a blockage in the carotid artery and is cause for further investigation.
• Digital subtraction angiography (D.S.A.) - In this imaging procedure, a contrast dye is injected into a vein in the arm and allowed to circulate in the bloodstream. Once the dye reaches the brain, an x-ray machine quickly takes a series of images or pictures of the head and neck. The images track the movement of the contrast dye as it proceeds through the blood vessels of the brain. This imaging technique allows the doctor to identify and localize the source of stroke, whether it be ischemic (result of blockage) or hemorrhagic (result of bleeding