Medical Imaging Techniques Quiz

Imaging Modalities

• Medical imaging modalities are used to visualize internal body structures.
• An introduction to medical imaging was presented.
• This course is titled HSMI 1211.
• The objectives included historical development, principles of modalities (radiography, CT, MRI, US, RNI), imaging parameters, and advantages/disadvantages of each modality.

Historical Development

• X-rays were discovered in 1895 by Wilhelm Conrad Roentgen.
• The first use of diagnostic imaging and medicine occurred in the 1950s.
• Magnetic Resonance Imaging (MRI) was developed in the 1980s, using a magnetic field without ionizing radiation.
• Digital imaging and artificial intelligence integration became prominent in the 2000's.
• Computed Tomography (CT) was developed in the 1970s, by Godfrey Hounsfield & Allan Cormack.
• SPECT and PET scans appeared in the 1990s.

General X-ray

• X-rays interact with tissues, either by transmission (passing through less dense tissues like air or soft tissue) or absorption (being absorbed by denser tissues like bone).
• X-ray beams are generated by an X-ray tube, pass through the patient, and interact with tissues.
• The image is formed by the varying amount of X-rays absorbed or transmitted.
• X-rays are composed of three components: X-ray tube, patient, and image receptor.

Imaging Parameters (kVp)

• Kilovoltage (kV) determines the penetrating power of the radiation beam.
• Higher kV results in more penetrating beams (leading to overpenetration) decreasing contrast, and increasing blackness.
• Higher kV results in less radiation being absorbed by tissues, lowering patient radiation dose.
• The anode is positively charged and the cathode is negatively charged, thus electrons move quickly leading to higher energy X-rays

Imaging Parameters (mA)

• Milliamperage (mA) denotes the current in the X-ray tube.
• Higher mA increases the intensity of the X-ray beam; causing the image to be darker and resulting in higher exposure.
• Increasing mA increases the radiation intensity.
• Increasing mA increases the radiation dose to the patient.

Imaging Parameters (Seconds)

• Measured in seconds, exposure time relates to the duration of radiation exposure.
• Longer exposure times result in more radiation reaching the patient, leading to a darker image.
• Increasing exposure time increases radiation dose to the patient.

Imaging Parameters (SID)

• Source-to-Image Receptor Distance (SID) is the distance between the X-ray source and the image receptor.
• Following the inverse square law, an increase in distance reduces the intensity of radiation, leading to underexposure.

Imaging Parameters (Image Receptor)

• The image receptor records the image.
• The speed of the image receptor system affects the amount of radiation needed to produce an image.
• Faster systems need less radiation for the same image density.

Imaging Parameters (Filtration)

• Filtration in X-ray tubes uses filters to remove low-energy X-rays.
• This reduces the intensity of radiation reaching the image receptor, making the image less black (underexposed).
• Increase in filtration reduces radiation dose to the patient.

Imaging Parameters (OID)

• Object-to-Image Receptor Distance (OID) is the distance between the patient and the image receptor.
• Increasing OID results in less radiation reaching the image receptor, giving rise to underexposure.
• OID also magnifies the image, decreasing the detail of the image.

General X-ray Advantages and Limitations

• Lack of depth information, structures superimposed
• Limited tissue differentiation compared to other modalities.
• False size due to magnification by image distance
• Advantages include simplicity, cost-effectiveness and accessibility.

Mammography

• Mammography uses a specific anode in the X-ray tube (molybdenum or molybdenum/tungsten alloy) enabling the use of lower kVp (28-32kV) when compared to conventional X-ray (50-120kV).
• Medio-lateral oblique (MLO) and cranio-caudal (CC) projections are commonly employed.

Fluoroscopy

• Fluoroscopy is an extension of radiography, providing real-time imaging.
• It shows the anatomy dynamically.
• Key improvements from conventional radiography lie in the ability to show changes in real-time.

Mobile X-ray

• Mobile X-ray allows for imaging in places outside of dedicated radiology departments.
• Image quality potentially less than in a fixed facility, due to lower specifications of the equipment.

Computed Tomography (CT) Scan

• CT generates cross-sectional images using multiple X-ray projections and computer processing.
• This overcomes the limitations of conventional X-ray (i.e., lack of depth information).
• This allows the user to see various perspectives through CT scans in different planes (e.g., AP, PA, lateral)

CT Imaging Parameters

• Key parameters like Kilovoltage (kV), Milliamperes (mA), exposure time, collimation (beam width), slice thickness, and more determine image quality and patient dose.
• Multi-planar reformation enhances image visualization.

CT System Components

• The CT system includes components for data acquisition, processing, display, archive, and communication.
• These include the control system, data acquisition system, data processing system, data display, data storage and communication systems.

Magnetic Resonance Imaging (MRI)

• MRI uses a powerful magnetic field and radio waves to produce detailed images of the body.
• This contrasts sharply with ionizing X-rays in medical imaging in that it does not use ionizing radiation.
• Key strengths include detailed tissue discrimination in different planes.
• Common imaging parameters include repetition time (TR), echo time (TE), inversion time (TI), flip angle (FA), and spin-spin relaxation time (T2).

MRI Imaging Parameters

• Key imaging parameters used in MRI are repetition time (TR), echo time (TE), Inversion time (TI), Flip angle (FA), spin-lattice relaxation time (T1). and spin-spin relaxation time (T2).

MRI Advantages & Limitations

• MRI offers superior tissue differentiation.
• It doesn't utilize ionizing radiation, minimizing potential risks.
• Images can be acquired in multiple planes without repositioning the patient.
• However, the procedure can be time-consuming & uncomfortable, sensitive to motion, and potentially dangerous with metallic implants.

Ultrasound

• Ultrasound utilizes sound waves to create images of internal body structures.
• Important parameters include frequency and gain to improve the image for the user.
• Advantages include portability, real-time imaging, and non-ionizing radiation.

Ultrasound Imaging Parameters

• The frequency is a crucial component of ultrasound imaging, where higher frequencies provide better resolution for shallower structures; lower frequencies penetrate deeper but have poorer resolution.
• Gain is another vital parameter that controls the amplification of attenuated echoes to create a better contrast and visualization of the structures and their differences from a darker background.

Ultrasound Advantages & Limitations

• Ultrasound offers portability, real-time imaging, and doesn't use ionizing radiation.
• However, it can't penetrate bone or air-filled structures, and image quality depends on the operator's skills and experience.

Radionuclide Imaging (RNI)

• Radioactive tracers, or radiopharmaceuticals, are introduced into the body, and their radiation is detected to visualize metabolic and functional processes.
• This includes SPECT for 3D imaging and PET, which combines metabolic function with anatomical information.

RNI Imaging Parameters

• SPECT uses gamma cameras, while PET combines metabolic information with CT.
• This provides functional images for physiological processes.
• Specific radionuclides like fluorine-18 (FDG), are critical tracers in PET imaging for oncology.

RNI Advantages & Limitations

• RNI yields unique information on physiological processes.
• RNI detects disease at early stages and allows whole-body scans.
• However, RNI has factors like limited accuracy due to signal limitations and prolonged scanning duration from tracer absorption and detection.

Choice of Imaging Modality

• The choice of imaging modality is based on the intended information and patient factors.
• Factors include the intended information, patient factors (e.g., claustrophobia; trauma), and required examination time.
• MRI and ultrasound may not demonstrate bony pathology.

Test your knowledge on various medical imaging techniques including SPECT, MRI, and PET. This quiz covers primary functions, advantages, and disadvantages of these modalities, helping you understand their applications in a clinical setting.