Radiation Hazards, Radiation Therapy, CT Scan, MRI, Scintigraphy,Doppler

RADIATION HAZARDS AND ADOPTION OF SAFETY INCREASERS

Dangers of radiations

• Ionising radiation used in diagnostic radiography is potentially harmful and if proper protective measure are taken the risk is small compared with the benefit to the patient.
• Certain tissues especially those which contains many multiplying cells, such as blood forming organs (bone marrow, lymphoid tissue, spleen), the gonads, embryos and cetain tumours are radiosensitive.
• X-rays have long term effect of producing Cancer, long after irradiation injury has healed.

RADIATION THERAPY - PRINCIPLES, ISOTOPES AND THEIR USES IN DIAGNOSIS AND THERAPY

RADIATION THERAPY - INTRODUCTION

• Radiation therapy for the treatment of neoplasm of domestic animals has been used since the discovery of X-ray. Dr. R. Eberlin was the first to report on the use of radiotherapy in veterinary practice.
• It kills malignant cells by decreased oxygen supply, decreased blood supply and damage to DNA.
• Radiotherapy is usually indicated for localised solid neoplasm’s that cannot be excised completely. It is not indicated if neoplasm has the potential of high incidence of metastasis.

• The other indication are :

1.      When surgery is expected to or has already failed.

2.      When the regional or distant metastasis not occurred.

3.      When radical surgery is unable to remove whole of the neoplasm.

4.      When bulk of the neoplasm needs reduction in size so that it can subsequently be removed surgically.

5.      Adjunct to chemotherapy

• Radiotherapy is not done by a single dose, rather multiple treatments are given over a period of time, termed fractioned therapy. In animals, it is usually in 10-12 fractions of a radiation dose of 4-5 Gy each time, usually three times per week.

METHODS OF RADIOTHERAPY

Teletherapy 

• The radiation source is kept at a distance from the lesion. It is of four types

• Superficial X-ray therapy: Given through X-ray machine with energy range of 60-100 keV.
• Deep X-ray therapy: Given through X-ray machine with energy range of 100- 200 keV.
• Super voltage therapy: Provided through (i) X-ray machine having linear accelerator or betatron or cyclotron, (ii) isotropic X-ray machine with cobalt or cesium. It is used in deep and substantial lesions
• Particulate beam therapy: Electron, neutron or proton beam can also be used as a mode of teletherapy.
  Brachytherapy 

• It is the therapeutic use of radioisotope either within the interstitium or on the surface of a neoplasm. The isotopes used are 198 Au , 60 Co, 125 K. Specific methods of brachytherapy are
  • Interstitial brachytherapy: Sources of radiation are within the interstitium of the neoplasm.
  • Pliesotherapy: It is surface brachytherapy for superficial lesions.
  • Systemic brachytherapy: 132 I and 32 P can be used systemically. It is used in extensive lesions and specific malignant conditions.

COMPLICATIONS OF RADIOTHERAPY

• Complications of radiotherapy are

• Immediate (minute to days): epilation, erythema , hematological depression and GI disturbances and chromosomal aberration.

• Latent (months to years): leukemia , life span shortening , cancer, lethal gene expression etc.

DIGITAL RADIOGRAPHY (DR)

Basic principles

• It involves translating x-ray energy into an electric signal that is in turn converted to digital data (numbers).
• The process may be direct, indirect, or hybrid.
•  In direct DR, the x-ray energy is converted directly into an electrical signal.
• In indirect DR, the x-ray energy is first converted to light by using a phosphorescent plate; the light is then converted to an electrical pulse.
• The data are recorded on a plate, which is connected to a computer, and the x-ray image is available for viewing almost immediately after exposure. It can then be stored or printed out.   
•  DR  images are stored on a computer hard drive and should be saved as DICOM (Digital Imaging and Communication in Medicine) files.   
• These images may be manipulated in multiple ways, including adjusting brightness and contrast, applying sharpening filters, inverting the image, and magnifying part or all of the image.

COMPUTED TOMOGRAPHY (CT)

Basic principles

• CT is an imaging method that uses the principles of tomography. Tomography is the demonstration of a slice through the body displayed without interference from structures lying above or below the level under examination.
• CT uses x-rays generated by a high-output x-ray tube. The tube is mounted on a gantry opposite a series of detectors. The tube and the detectors rotate in unison around the subject under examination. A fan-shaped beam of x-rays passes through the body at a predetermined level.
• The pattern of x-rays that reaches the detectors is recorded—a projection. The entire gantry assembly is then rotated slightly, and the procedure is repeated, generating a new projection. A series of such projections is obtained, completely encompassing the body under examination.
• A computer uses complex mathematical formulas to create an image from the series of projections. This image represents a slice of the body at the level under examination.
• The advantage of CT is its ability to distinguish different types of soft tissue, such as brain white and gray matter or liver and gallbladder. CT achieves this degree of contrast by being able to measure very fine differences in the ability of tissues to stop x-rays passing through them.
• CT images are digital, and a computer is used for viewing. The gray scale can be adjusted to highlight specific features such as bone or soft tissue (windowing). In CT imaging, tissues and structures are described in terms of attenuation, which is a measure of the capacity of a tissue to stop x-rays. Attenuation is equivalent to radiopacity in radiography. The appearance of a tissue is defined in relation to some reference tissue or its expected normal appearance.      

ECOCARDIOGRAPHY - PRINCIPLES AND ITS APPLICATION

DOPPLER ULTRASOUND

• A Doppler ultrasound test uses reflected sound waves to see how blood flows through a blood vessel. It helps to evaluate blood flow through major arteries and veins, such as those of the legs and neck.
• It can show blocked or reduced blood flow through narrowing in the major arteries of the neck that could cause a stroke. It also can reveal blood clots in leg veins (deep vein thrombosis, or DVT) that could break loose and block blood flow to the lungs (pulmonary embolism).
• During pregnancy, Doppler ultrasound may be used to look at blood flow in an unborn baby (fetus) to check the health of the fetus.
• During Doppler ultrasound, a handheld instrument (transducer) is passed lightly over the skin above a blood vessel. The transducer sends and receives sound waves that are amplified through a microphone. The sound waves bounce off solid objects, including blood cells.  
• Information from the reflected sound waves can be processed by a computer to provide graphs or pictures that represent the flow of blood through the blood vessels. These graphs or pictures can be saved for future review or evaluation.   

APPLICATIONS OF DOPPLER ULTRASOUND

• Non-invasive
• Generally painless
• Does not use radiation
• Can show if you have any blocked arteries in neck, arms, abdomen, coronary arteries and limbs
• Can show if you have any blood clots in the veins in limbs
• Can show the amount and speed of blood flow in your veins and arteries  

NUCLEAR SCINTIGRAPHY

• Scintigraphy ("scint," Latin scintilla, spark) is a form of diagnostic test used in nuclear medicine, wherein radioisotopes (here called radiopharmaceuticals ) are taken internally, and the emitted radiation is captured by external detectors (gamma cameras) to form two-dimensional images.
• The principle is based on the use of pharmaceutical labelled with radioisotope which after entry into the blood stream get localised in particular tissue or organ. Thus the localisation of radioisotope can be detected by using camera due to emission of gamma rays. Most widely used radioisotope is Technetium-99m. This isotope has the advantage of a short half life of 6hrs and thus animal can be discharged next day after the scan . in addition, radiation exposure is minimum.
• The distribution of the labelled isotope can be detected by a gamma camera or a hand held detector. In both the case sodium iodide crystalis used which absorbs gamma rays emitted by the radioisotope from the patient and converts it to light flashes. The light is converted to an electrical impulse. This impulse is shown on a oscilloscope or converted to an image. Image can be produced in colours or in a grey colour.    
• Problems associated with scintigraphy are

1.      Cost of the gamma camera

2.      Precise and strict safety precautions required.

3.      Non specificity to the aetiology and difficulty encountered some times in interpreting the scan especially skeletal system

Magenetic Resonance Imaging

Anatomy and function of body in health and disease is revealed by magnetic and radiowaves to form a image.No radiation is involved.

In 1952, Herman Carr has invented one dimensional MRI.

The patient in MRI Scanner –

 Strong magnetic field, around area to be imagined.

Water molecules in body, with excited Hydrogen atoms are seen.

Radiofreuency signal with oscillating magnetic field is at appropriate resonant frequency.

Characteristic repetitive noises recorded as MRI scan.

Contrast can be given by I/V, Oral, Intraarticular methods.

Contraindications:

Pace makers

Bone screws, plates

Chochlear implants

Ferromagnetic surgical implants

Sharpnels