Diagnostic Imaging

Lasers produce electromagnetic radiation (light). In surgical applications, the electromagnetic waves are focused to cut or cauterize tissue.

This is the correct answer. An MRI (or magnetic resonance imaging) scan is a radiology technique that uses magnetism, radio waves, and a computer to produce images of body structures.

PET (Positron Emission Tomography) imaging is a nuclear medicine technique that uses radiotracers to measure metabolic processes and blood flow, including cerebral blood volume.

PET scans use radiotracers, which are isotopes of elements like carbon, nitrogen, or oxygen that are naturally found in the body. These tracers allow for the visualization of metabolic processes in living tissue.

X-ray crystallography is a tool used for identifying the atomic and molecular structure of a crystal, in which the crystalline atoms cause a beam of incident X-rays to diffract into many specific directions. By measuring the angles and intensities of these diffracted beams, a crystallographer can produce a three-dimensional picture of the density of electrons within the crystal. From this electron density, the mean positions of the atoms in the crystal can be determined, as well as their chemical bonds, their disorder and various other information.

Ultrasonic waves are used in sonography for the mapping of body organs. The Ultrasonic waves that are sent inside the body are reflected from the different parts by creating the echo. They are more useful and less harmful than radiation.

Electrocardiography is a medical diagnostic

techniques, ultrasonic waves are used to construct the image of the heart, for

monitoring a nuclear reactor.

Ultrasound can be used in 

The options in the question are given unnecessarily. It can be a direct question.
Below are the applications of ultrasound.

• Ultrasound has been used in a variety of clinical settings, including obstetrics and gynecology, cardiology and cancer detection. The main advantage of ultrasound is that certain structures can be observed without using radiation. Ultrasound can also be done much faster than X-rays or other radiographic techniques. 
• Ultrasound is well known to have a significant effect on the rate of various processes in the food industry. Using ultrasound, full reproducible food processes can now be completed in seconds or minutes with high reproducibility, reducing the processing cost, simplifying manipulation and work-up, giving higher purity of the final product, eliminating post-treatment of waste water and consuming only a fraction of the time and energy normally needed for conventional processes. Several processes such as freezing, cutting, drying, tempering, bleaching, sterilization, and extraction have been applied efficiently in the food industry. The advantages of using ultrasound for food processing, includes: more effective mixing and micro-mixing, faster energy and mass transfer, reduced thermal and concentration gradients, reduced temperature, selective extraction, reduced equipment size, faster response to process extraction control, faster start-up, increased production, and elimination of process steps. Food processes performed under the action of ultrasound are believed to be affected in part by cavitation phenomena and mass transfer enhancement. 
• Ultrasound is used in the synthesis of nanostructured materials.
• Devices limited to low ultrasonic frequencies, have a number of industrial applications, including drying, ultrasonic cleaning, and injection of fuel oil into burners. 

There are different types of treatment for cancer. They are:

• Surgery: Surgery can be used to diagnose, treat or even help prevent cancer in some cases.
• Radiation therapy uses high-energy particles or waves to destroy or damage cancer cells.
• Chemotherapy is the use of the medicines or drugs to treat cancer.

• Radiotherapy is the use of electromagnetic radiations such as X-rays, gamma rays, electron beams or protons to kill or damage cancer cells to stop/slow them from growing or multiplying.
• Radiotherapy can take place before, during or after treatment or in conjugation with other treatments such as chemotherapy treatment.
• Hence Treatment of cancer by X-rays or Gamma rays is Radiotherapy.
• So, the correct answer is 'Radiotherapy'.

Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. Treatment of cancer includes - 

Electron therapy or Electron Beam Therapy (EBT) is a kind of external beam radiotherapy, where electrons are directed to a tumor site. Electron beam therapy is performed using a medical linear accelerator. The same device can also be used to produce high energy photon beams. When electrons are required, the x-ray target is retracted out of the beam and the electron beam is collimated with a piece of apparatus known as an applicator or an additional collimating insert, constructed from a low melting point alloy. Electron beam therapy is used in the treatment of superficial tumors like cancer of skin regions, or total skin (e.g., mycosis fungoides), diseases of the limbs (e.g., melanoma and lymphoma), nodal irradiation, and it may also be used to boost the radiation dose to the surgical bed after mastectomy or lumpectomy. 

Answer is D.

Technique of echocardiography is based on reflection property of ultrasonic waves.
An echocardiogram (also called an echo) is a type of ultrasound test that uses high-pitched sound waves that are sent through a device called a transducer. The device picks up echoes of the sound waves as they bounce off the different parts of our heart. These echoes are turned into moving pictures of our heart that can be seen on a video screen.