COMPUTED TOMOGRAPHY

1. In the two decades since computed tomography (CT) was introduced by Sir Godfrey Hounsfield it has become established as a powerful diagnostic tool and one that is relevant to many branches of surgery. Used appropriately, CT is capable of making a major impact on management decisions.

2. The essence of the CT technology is that the scanner rotates an X-ray tube around the patient in an arc and the emergent radiation beam is measured by photoelectric detectors. A computer is used to display the measurements of the patient, based on the density of tissues to X-rays. The image can be thought of as a cross-sectional radiograph but unlike radiography there is no superimposition of structures and the detector/computer system makes the technique very sensitive.

3. From the patient’s point of view CT examination is simple. In the majority of examinations all the patient has to do is lie on the couch while the machine makes the readings. Examination is usually carried out with the patient supine, although specialized indications may require specific positions. Exposures typically last a few seconds, and suspended respiration is required when the chest or abdomen are being examined; a diagnostic examination may not be possible if the patient has difficulty holding their breath, as respiratory movement may cause artifact. Other areas can be studied during quiet respiration.

4. The CT section is a cross-sectional radiograph in which tissues are displayed on a grey scale according to their attenuation value. Dense structures such as cortical bone appear light, whereas low density areas like air appear dark, as in the case with conventional radiographs. The attenuation of tissues on CT is displayed on a wider scale than can be shown effectively on one image, however. The display console therefore allows the image to be manipulated so that areas at different points on the attenuation scale can be examined. The basic image data can also be manipulated in other ways. Measurements from a small area can be reprocessed to give a high resolution image, this is useful for demonstrating small structures. Information may also be reformatted in different planes, on three-dimensional perspective views, to provide a more anatomical display.

5. The principal advantage of CT is that it provides a clear, accurate display of tissues without superimposition of structures. Disease processes may be detected at an earlier stage than is possible with other techniques, and lesions may be detected in areas which are difficult to assess with conventional imaging. The technique is not limited to specific organs: since all of the tissues in a body section are displayed it can be used to search for disease sites.

6. Although CT is effective in disease detection and localization, characterization of lesions is more difficult, since many have similar attenuation characteristics. The other main disadvantages of CT are high capital cost of the equipment and the fact that it employs ionizing radiation. CT is therefore used with care around radiosensitive structures such as the eye, or in children and young people, and only for over-riding indications in pregnant women.

7. Although the capital and running costs of CT are high, the technique is undoubtedly cost effective. It can be used to achieve an early diagnosis in patients who would otherwise need to undergo a large number of alternative investigations, and it can be performed on an outpatient basis, reducing costs for inpatient investigation. Moreover, the diagnostic and therapeutic applications of CT frequently replace exploratory laparotomy, or other major surgical procedures.

8. In the future the clinical role of CT will need to be reassessed as MRI develops. For the present, CT is the mainstay of cross-sectional imaging.

V. In paragraphs 2 and 3 find English equivalents of the following words and word combinations: cущность технологии, рентгеновская трубка, возникающий радиационный луч, плотность тканей, радиограф с поперечным сечением, лежать на кушетке, пациент в положении лежа, специальные указания, приостановленное дыхание, грудная клетка, брюшная полость.

VI. In paragraph 2 find the information about the essence of examination.

VII. Look through paragraph 3 and say how the procedure is performed.

VIII. Read paragraphs 5 and 6 and answer the questions.

IX. Read paragraph 7 and explain why the technology of CT is undoubtedly cost effective.

X. Say whether the following statements are true or false.

XI. Complete the following sentences choosing the most suitable variant.

XII. Speak about CT as a powerful diagnostic tool.

Part B

I. Define the meaning of the “x” word.

II. Find in the list the following parts of speech: a) nouns, b) adjectives, c) adverbs, d) verbs.

Emission, physiologic, emit, evaluate, responsive, surgery, scanner, multiple, permit, attach, commonly, appropriate, brightness, accumulate, restriction, plenty, exposure, affect, enhance.

III. Complete the sentences with the following words: are not responsive, are displayed, exposure, detection, radioactive, radiologist, colors, brightness, alterations.

IV. Read the text and entitle it.

Positron emission tomography, also called PET imaging or PET scan, is a diagnostic examination that involves the acquisition of physiologic images based on the detection of radiation from the emission of positrons. Positrons are tiny particles emitted from a radioactive substance administered to the patient. The subsequent images of the human body developed with this technique are used to evaluate a variety of diseases.

PET scans are used most often to detect cancer and to examine the effects of cancer therapy, heart diseases, brain tumors or seizure disorders that are not responsive to medical therapy and are therefore candidates for surgery.

The PET scanner has a hole in the middle and looks like a large doughnut. Within this machine are multiple rings of detectors that record the emission of energy from the radioactive substance in your body and permit an image of your body to be obtained. While lying on a cushioned examination table, you will be moved into the hole of the machine. The images are displayed on the monitor of a nearby computer, which is similar in appearance to the personal computer you may have at home.

Before the examination begins, a radioactive substance is produced in the machine called a cyclotron and attached, or tagged, to a natural body compound, most commonly glucose, but sometimes water or ammonia. Once this substance is administered to the patient, the radioactivity localizes in appropriate areas of the body and is detected by the PET scanner. Different colors or degrees of brightness on a PET image represent different levels of tissue or organ function. For example, because healthy tissue uses glucose for energy, it accumulates some of the tagged glucose, which will show up on the PET images. However, cancerous tissue, which uses more glucose than normal tissue, will accumulate more of a substance and appear brighter than normal tissue on the PET images.

The procedure may take 30 to 45 minutes. It must be done by a radiologist who has specialized in nuclear medicine and has substantial experience with PET. A radiologist who has specialized training in PET will interpret the images and forward a report to your referring physician. Usually, there are no restrictions on daily routine after the test, although you should drink plenty of fluids to flush the radioactive substance from your body. Because PET allows study of body function, it can help physicians detect alterations in biochemical processes that suggest disease before changes in anatomy are apparent with other imaging tests, such as CT or MRI. Because radioactivity is short-lived, your radiation exposure is low. The substance amount is so small that it does not affect the normal processes of the body.

Finally, the value of a PET scan is enhanced when it is a part of a larger diagnostic work-up. This often entails comparison of the PET scan with other imaging studies, such as CT or MRI.

V. Read the text and say which paragraph contains the information about some common uses of the procedure.

VI. Say whether the following statements are true or false.

VII. Match parts of the sentences.

VIII. Give a short summary of text B.

Part C

I. Read the text and define its main idea.

MAGNETIC RESONANCE IMAGING (MRI)

Magnetic resonance imaging (MRI) also called magnetic resonance tomography (MRT) is a method of creating images of the inside of opaque organs in living organisms as well as detecting the amount of bound water in geological structures. It is primarily used to demonstrate pathological or other physiological alterations of living tissues and is a commonly used form of medical imaging. MRI has also found many novel applications outside of the medical and biological fields such as rock permeability to hydrocarbons and certain non-destructive testing methods such as produce and timber quality characterization.

MRI was developed from knowledge gained in the study of nuclear magnetic resonance. The original name for the medical technology is nuclear magnetic resonance imaging (NMRI), but the word nuclear is almost universally dropped. This is done to avoid the negative connotations of the word nuclear, and to prevent patients from associating the examination with radiation exposure, which is not one of the safety concerns for MRI. Scientists still use an NMR when discussing non-medical devices operating on the same principles. Unfortunately the devices themselves are very expensive with several hundred thousands dollars per year upkeep costs.

In clinical practice MRI is used to distinguish pathological tissue (such as brain tumor) from normal tissue. One of the advantages of an MRI scan is that, according to current medical knowledge, it is harmless to the patient. It utilizes strong magnetic fields and non-ionizing radiation in the radio frequency range. Compare it to CT scans and traditional X-rays which involve doses of ionizing radiation and may increase the chance of malignancy, especially in children receiving multiple examinations.

The typical MRI examination consists of 5-20 sequences, each of which are chosen to provide a particular type of information about the subject tissues. This information is then synthesized by the interpreting physician. The presence of a ferromagnetic foreign body in the subject, or a metallic implant (like surgical prostheses, or pacemakers) can present a (relative or absolute) contraindication towards MRI scanning: interaction of the magnetic and radiofrequency fields with such an object can lead to: trauma due to the shifting of the object in the magnetic field, thermal injury from radiofrequency induction of heating of the object, or failure of an implanted device.

Because of MRI’s superior imaging of soft tissues, it is now being utilized to specifically locate tumors within the body in preparation for radiation therapy treatments. For therapy simulation, a patient is placed in specific, reproducible, body position and scanned. The MRI system then computes the precise location, shape and orientation of tumor mass, correcting for any spatial distortion inherent in the system. The patient is then marked or tattooed with points which, when combined with the specific body position, will permit precise triangulation for radiation therapy.

II. Read the text and answer the questions.

III. Using information from the text name advantages of the MRI procedure.

IV. Read the text and describe a typical MRI examination.

V. Give the main points of the text in 5-6 sentences.