Radiation Physics and Protection Practice Questions

Q: Hounsfield units are used in CT density scale to measure attenuation value of different materials compared to water. The value of fat in HU would be around:

-100. ***-100*** - **Fat** has a lower density than water, causing less X-ray attenuation. This results in negative Hounsfield Unit (HU) values. - A value of **-100 HU** is characteristic for fat, indicating its low density compared to the reference point of water (0 HU). *100* - A value of **100 HU** typically represents soft tissues that are denser than water but less dense than bone, such as muscle or early stages of hemorrhage. - This value indicates a higher X-ray attenuation than fat, which is contrary to the properties of fat. *1000* - A value of **1000 HU** is characteristic of **dense bone** or calcifications, which strongly attenuate X-rays due to their high density and atomic number. - This significant positive value is far from the negative values associated with fat. *-1000* - A value of **-1000 HU** represents **air**, which has the lowest density and therefore the lowest X-ray attenuation, appearing black on CT images. - While negative, this value is much lower than that of fat, indicating a significantly less dense material.

Q: Which of the following radioisotopes has the longest half-life?

C – 14. ***C – 14*** - **Carbon-14** is a **radionuclide** with a half-life of approximately **5,730 years**, making it the longest among the given options by a significant margin. - Its long half-life allows it to be used in **radiocarbon dating** of ancient artifacts and biological samples. *Co – 60* - **Cobalt-60** has a half-life of **5.27 years**. - It is known for emitting **gamma rays** and is used in **radiotherapy** and industrial sterilization. *I – 125* - **Iodine-125** has a relatively short half-life of approximately **59.4 days**. - It is frequently used in **brachytherapy** for prostate cancer and in **radioimmunoassays**. *P – 32* - **Phosphorus-32** has a half-life of approximately **14.3 days**, one of the shortest among the options. - It's commonly used as a **radioactive tracer** in molecular biology research.

Q: To obtain adequate diagnostic imaging in a morbidly obese patient, what modification to X-ray technique is most important?

Increase KVP. ***Increase KVP*** - Increasing the **kilovoltage peak (KVP)** is essential for imaging morbidly obese patients because it increases the **penetrating power** of the X-ray beam, allowing adequate transmission through thick body tissues. - Higher KVP (typically 90-120 kVp range) ensures the X-ray beam can penetrate increased soft tissue thickness and reach the image receptor with sufficient intensity. - While higher KVP produces **longer scale (lower) contrast**, it is necessary for adequate **penetration** in obese patients - without sufficient KVP, the image would be underexposed and non-diagnostic. - In practice, both KVP and MAS are increased for obese patients, but **KVP increase is more critical** for penetration. *Increase MAS* - Increasing **milliampere-seconds (MAS)** increases the quantity of X-ray photons and image density (brightness), which is also helpful for obese patients. - However, MAS alone without adequate KVP cannot solve the penetration problem - the photons would still be too low energy to penetrate thick tissues effectively. - MAS increase without KVP increase would result in high patient dose with poor image quality. *Decrease KVP* - Decreasing KVP reduces **beam penetration**, which would be catastrophic for imaging an obese patient. - The X-ray beam would be absorbed by superficial tissues, resulting in a severely **underexposed** and non-diagnostic image. - While lower KVP produces higher contrast in theory, it is completely inappropriate for thick body parts. *Decrease MAS* - Decreasing MAS reduces the number of X-ray photons, resulting in an **underexposed, lighter** image. - This would make it even more difficult to obtain adequate imaging through increased body mass, resulting in a non-diagnostic radiograph with excessive quantum mottle.

Q: SI unit of Radioactivity is

Becquerel. ***Becquerel*** - The **Becquerel (Bq)** is the **SI unit of radioactivity**, defined as one **disintegration per second**. - It quantifies the number of **radioactive decays** occurring in a material over a specific time. *Roentgen* - The **Roentgen** is an outdated unit used to measure the **exposure to gamma or X-rays**, specifically the amount of ionization in air. - It does not directly quantify the **activity of a radioactive source**. *Sievert* - The **Sievert (Sv)** is the **SI unit of equivalent dose**, which measures the **biological effect of radiation** on living tissue. - It accounts for the type of radiation and its potential harm, rather than the raw decay rate. *Curie* - The **Curie (Ci)** is an older, non-SI unit of radioactivity, equivalent to **3.7 × 10^10 disintegrations per second**. - It was historically defined based on the activity of **one gram of radium**.

Q: What is the role of fixer?

It removes the extra silver halides which are unfixed.. ***It removes the extra silver halides which are unfixed.*** - The fixer solution plays a crucial role in creating a permanent radiographic image by **dissolving and removing all unexposed and undeveloped silver halide crystals** from the film emulsion. - This process prevents the film from darkening over time and ensures that only the areas exposed to radiation, forming the latent image, remain visible. *It binds developer to film.* - The developer's role is to **convert exposed silver halide crystals into metallic silver**, creating the visible image, but it does not bind to the film permanently. - The fixer step follows development to remove unexposed crystals, not to bind the developer. *It takes away extra developer solution.* - While the fixer follows the developer bath, its primary role is not simply to remove residual developer solution; that function is more closely associated with the **rinse step** between development and fixing. - The main action of the fixer involves chemical removal of silver halides. *It strengthens/fixes the silver halides on to X-ray film.* - The developer is responsible for converting exposed silver halides into visible silver, but the fixer actually **removes the *unfixed*** silver halides, rather than strengthening or "fixing" them onto the film. - This removal is essential for a stable and clear image, as any remaining unfixed halides would eventually darken.

Q: X-rays cause radiation damage primarily by their property of:

Ionisation. ***Correct: Ionisation*** - X-rays are a form of **ionising radiation**, meaning they have sufficient energy to **remove electrons from atoms**. - This process creates **ions** and free radicals, which can damage DNA and other cellular components, leading to radiation damage. *Incorrect: Radioactivity* - **Radioactivity** refers to the spontaneous emission of radiation from unstable atomic nuclei, a property of certain isotopes, not X-rays themselves. - While radioactive substances can emit various forms of radiation, including X-rays, the X-ray's damaging property is its ability to ionise, not its origin from a radioactive source directly. *Incorrect: Penetration* - The **penetrating power** of X-rays allows them to pass through tissues and is essential for imaging, but it is not the direct mechanism of biological damage. - Their ability to pass through matter facilitates interaction with atoms throughout the body, making ionisation possible. *Incorrect: Electromagnetic induction* - **Electromagnetic induction** is the production of an electromotive force across an electrical conductor in a changing magnetic field, a principle used in generators and transformers. - This phenomenon is unrelated to the biological effects or primary mechanism of radiation damage from X-rays.

Q: What is the full form of DICOM?

Digital imaging and communications in medicine. **Digital imaging and communications in medicine** - **DICOM** is the international standard for managing and transmitting medical images and related data, ensuring **interoperability** between different medical imaging equipment and systems. - Its purpose is to facilitate the storage, retrieval, management, and exchange of **medical images**, such as X-rays, CT scans, and MRIs, regardless of the vendor. *Direct imaging and colors in medicine* - This option incorrectly describes the purpose and scope of DICOM, which is broader than just "direct imaging" and "colors." - The standard focuses on the **digital nature** of medical images and the **communication** between devices. *Digital information and connectivity in medicine* - While DICOM deals with "digital information" and "connectivity," this option omits the crucial aspect of "imaging" in its description. - The primary focus of DICOM is on **medical images** and their communication. *Dependent interconnectivity in medicine* - This phrase does not accurately represent the function or the components of the **DICOM standard**. - DICOM enables **independent connectivity** and interoperability rather than dependent interconnectivity.

Q: Dose of radiation per study in mammography is

2 cGy. ***2 cGy*** - The typical average glandular dose per **complete mammography study** is approximately **2 cGy (0.2 rad or 2 mGy)** for a standard two-view examination per breast. - With **modern digital mammography**, doses have been further reduced to approximately **0.4-0.8 cGy** per complete study, but **2 cGy** remains the commonly cited reference value for screening mammography in medical literature. - This dose is considered **safe for routine screening** with benefits far outweighing the minimal radiation risk. *4 cGy* - This value is **higher than the standard** radiation dose for modern mammography. - While older **film-screen mammography** systems delivered higher doses, **4 cGy** exceeds the typical exposure for a complete digital mammographic study. - This would represent an unnecessarily high dose with current technology. *3 cGy* - This value is **slightly higher** than the standard reference dose for mammography. - While closer than 4 cGy, **3 cGy** is still above the typical average glandular dose delivered in modern screening mammography. *1 cGy* - This value is **lower than the traditional reference** but actually closer to **modern digital mammography** doses (0.4-0.8 cGy per complete study). - However, in **standard medical literature and exam references**, **2 cGy** is the conventionally cited dose for mammography screening.

Q: Radioactive nuclides used in medical imaging that have the same atomic number but different mass numbers are termed:

Isotopes. ***Isotopes*** - Isotopes are atoms of the same element (same **atomic number** or number of protons) but with different mass numbers (different number of neutrons). - This property allows them to be chemically identical but have different nuclear properties, making them useful in **medical imaging** (e.g., technetium-99m). *Isobars* - Isobars are atoms with the same **mass number** but different atomic numbers (different elements). - They have different chemical properties and are not the primary basis for radioactive nuclides in medical imaging in this context. *Isomers* - Isomers are nuclides with the same atomic and mass numbers but in different **nuclear energy states**. - **Technetium-99m** is a metastable isomer widely used in nuclear medicine, but the definition in the question refers to variations in mass number for a given atomic number. *Isotones* - Isotones are atoms with the same number of **neutrons** but different numbers of protons (different elements). - Like isobars, they represent different elements and are not defined by having the same atomic number but different mass numbers.

Q: In CT scan, CT numbers range from:

-1000 to +1000. ***-1000 to +1000*** - CT numbers, also known as **Hounsfield Units (HU)**, represent the attenuation of X-rays in tissues relative to water. The range from -1000 to +1000 allows for a broad spectrum of tissue densities to be distinguished. - Air is assigned a value of **-1000 HU**, water is **0 HU**, and dense bone can be around **+1000 HU** (or higher for very dense materials like metal). * -100 to +100* - This range is too narrow to encompass the full spectrum of tissue densities encountered in the human body, particularly very dense structures like bone or very low-density structures like air. - While it might cover some soft tissue variations around water (0 HU), it would exclude crucial anatomical details. * 0 to 1000* - This range is insufficient as it does not include negative HU values, which are essential for representing air and fatty tissues. - Air, which has the lowest density, is typically assigned a value of -1000 HU. * 0 to 100* - This range is significantly too narrow and would only allow for the discrimination of a very limited set of tissues, primarily those with densities close to water. - It would completely exclude air, fat, and dense bone, making it impractical for diagnostic CT imaging.

Question 1

Hounsfield units are used in CT density scale to measure attenuation value of different materials compared to water. The value of fat in HU would be around:

Accepted Answer

-100

Answer

100

Answer

1000

Answer

-1000

Question 2

Which of the following radioisotopes has the longest half-life?

Accepted Answer

C – 14

Answer

Co – 60

Answer

I – 125

Answer

P – 32

Question 3

To obtain adequate diagnostic imaging in a morbidly obese patient, what modification to X-ray technique is most important?

Accepted Answer

Increase KVP

Answer

Increase MAS

Answer

Decrease KVP

Answer

Decrease MAS

Question 4

SI unit of Radioactivity is

Accepted Answer

Becquerel

Answer

Roentgen

Answer

Sievert

Answer

Curie

Question 5

What is the role of fixer?

Accepted Answer

It removes the extra silver halides which are unfixed.

Answer

It binds developer to film.

Answer

It takes away extra developer solution.

Answer

It strengthens/fixes the silver halides on to X-ray film.

Question 6

X-rays cause radiation damage primarily by their property of:

Accepted Answer

Ionisation

Answer

Radioactivity

Answer

Penetration

Answer

Electromagnetic induction

Question 7

What is the full form of DICOM?

Accepted Answer

Digital imaging and communications in medicine

Answer

Direct imaging and colors in medicine

Answer

Digital information and connectivity in medicine

Answer

Dependent interconnectivity in medicine

Question 8

Dose of radiation per study in mammography is

Accepted Answer

2 cGy

Answer

3 cGy

Answer

1 cGy

Answer

4 cGy

Question 9

Radioactive nuclides used in medical imaging that have the same atomic number but different mass numbers are termed:

Accepted Answer

Isotopes

Answer

Isobars

Answer

Isomers

Answer

Isotones

Question 10

In CT scan, CT numbers range from:

Accepted Answer

-1000 to +1000

Answer

-100 to +100

Answer

0 to 1000

Answer

0 to 100

Radiation Physics and Protection — MCQs

Radiation Physics and Protection — MCQs

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