MT training: radiology

Tomography. Tomography is a technique for taking a series of x-ray pictures, so that x-rays of a desired layer of the body are obtained, while at the same time structures in front of and behind that layer are blurred out. Multiple pictures, called tomograms or body secretions, are taken by changing the depth of focus of the x-ray machine while the patient remains still. Tomograms are thus x-ray “slices” taken at different depths of focus through the patient. Each tomogram obliterates all extraneous material and focuses on the one small slice that is to be view. Calcifications and other solid lesions that are missed on conventional x-rays can be picked up with tomography.

1. Ultrasound : The technique employs high-frequency, inaudible sound waves that bounce off body tissues and are then recorded to give information about the anatomy of an internal organ. An instrument is placed near or on the skin, which is covered with a thin coating of mineral oil to assure good transmission of sound waves. This instrument emits sound waves in short, repetitive pulses. The ultrasound waves move with different speeds through body tissues and detect interfaces between tissues of different density. An echo reflection of the sound waves is formed as the waves hit the various body tissue and pass back to the ultrasound monitor.

The ultrasonic echoes are then recorded as a composite picture of the area of the body over which the instrument has passed. The record produced by ultrasound is called a sonogram or echogram.

Ultrasound is used as a diagnostic tool not only by radiologists but also by neurosurgeons and ophthalmologists to detect intracranial and ophthalmic lesion, by cardiologists to detect heart valve and blood vessel disorder (echocardiography), by gastroenterologists to locate abdominal masses outside the digestive organ, and by obstetricians & gynecologists to differentiate single and multiple pregnancies as well as to help in performing amniocentesis and in locating tumors or cysts. Fetal size and age can also be measured using ultrasound. The measurements are made form ultrasound images taken in various fetal planes (across the head, abdomen, and femur).

Ultrasound has several advantages in that the sound waves are nonionizing and noninjurious to tissues at the energy ranges utilized for diagnostic purposes. Since water is an excellent conductor of the ultrasonic beams, patients are requested to drink large quantities of water prior to examination so that the urinary bladder will be distended and enable better viewing of pelvic and abdominal organs.

Two ultrasound techniques, Doppler ultrasound and color flow imaging, Make it possible to record blood velocity (in diagnosing vascular disease) and to image major blood vessels in patients at risk for stroke.

Ultrasound, like fluoroscopy, has also been used in interventional radiology to guide needle biopsies for the puncture of cysts and for the placement of needles for amniocentesis.

2. Magnetic Imaging or Magnetic Resonance Imaging (MRI) This technique produces sagittal, coronal (frontal), and axial (cross-sectional) images, the latter being similar to CT scanning. MRI, however, uses no x-rays and does not require a contrast medium. The technique is based on the fact that the nuclei of some atoms behave like little magnets when a larger magnetic field is applied. Thus nuclei spin and emit radio waves that create an image as the nuclei move back to an equilibrium position. Hydrogen nuclei, present in water and abundant in living tissue, are the nuclei used to create the image. MRI is useful in detecting edema in the brain, projecting a direst image of the spinal cord, detecting tumors in the chest and abdomen, and visualizing the cardiovascular system.