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Radiology: a medical specialty uses the imaging to both diagnose and treat disease visualized within the human body.

Radiologists use an array of imaging technologies to diagnose or treat diseases (X-ray radiography, ultrasound, computed tomography (CT), nuclear medicine, positron emission tomography (PET) and magnetic resonance imaging (MRI)).

Interventional radiology: the performance of (usually minimally invasive) medical procedures with the guidance of imaging technologies.

The acquisition of medical imaging is usually carried out by the radiographer or radiologic technologist. The radiologist then interprets or "reads" the images and produces a report of their findings and impression or diagnosis. This report is then transmitted to the ordering physician, either routinely or emergently.

• Initially, radiology was the science of 'X-rays', but today it involves a variety of imaging techniques to study and investigate patients so that a diagnosis can be achieved.

• In addition, therapeutic procedures are performed by radiologists under image guidance, a branch also known as interventional radiology.

What are the Different Imaging Modalities Radiography “plain films”

Computed axial tomography “CT”(Positron Imaging Tomography “PET”, Single Photon Emission CT “SPECT”, Combined PET-CT) Magnetic resonance imaging “MRI”

Ultrasound “US”

Interventional radiology “angio”

How to Approach Reading any Image

Identify the patient

When was the image taken

Are these the proper images

The five densities

Are the images technically adequate

Radiography – X - Ray Also called “plain films” or “standard films”

Image formed using broad beam ionizing radiation

The image formed is related to the subjects density

May involve the use of contrast agentsIodinated BariumAir

High Energy Photon --Kilo Electron Volts

Ionizing Radiation

Exposes Film / Detector

Projection Data

X-RAY

X-rays are short-wave electromagnetic radiation produced by accelerating electrons across an evacuated tube onto a tungsten anode using a high voltage.

• An X-ray tube is similar to a light bulb with a filament and a current to heat the filament.

• There is also a high voltage to accelerate the electrons from the filament at a target.

• This collision releases the x-ray radiation that is used to image the patient.

X-RAYS PLAIN FILM RADIOGRAPHY - Clinical uses

Chest Bones Spine / Extremities / Skull Soft tissue Mammography / Abdomen

These are the 5 typical body regions that the plain x-ray is used to evaluate.

Air / Gas

Soft Tissue / Fluid filled space

Bone

Fat

Metal

X - RAY --- FIVE BASIC DENSITIES

• The x-rays can traverse tissue to create the image.

• We can only separate the 5 basic densities noted. Air / Gas, Soft tissue / Fluid filled space, Bone, Fat & Metal.

• Here we see the Air in the lungs, the soft tissue of the heart and the bone density of the ribs.

• Water will appear of the same density as soft tissue and cannot be separated. Fat is difficult to see on the chest and better noted on abdominal x-rays

CONTRAST RADIOGRAPHY

Injection, ingestion, or other placement of opaque material within the body.

Improves visualization and tissue separation.

Can demonstrate functional anatomy and pathology.

Contrast agent: dense fluids containing elements of high atomic number

• Administering a contrast agent modifies the image to give more information.

Clinical uses :-

• Typical ones are barium, an inert particulate contrast used in GI tract evaluation.

• Iodine, a water soluble agent which can be injected into the vascular tree.(ANGIOGRAPHY) + intravenous agents to visualize the renal tract (intravenous pyelogram - IVP)

• Interventional procedures

UPPER GI--(GASTRO INTESTINAL)ORAL BARIUM CONTRAST

ARTERIOGRAM INTRAARTERIAL IODINE CONTRAST

• The contrast agent -Barium- will outline the GI tract, determine size and show patency or obstruction.

• The contrast agent-Iodine can be injected and is water soluble.

• In the blood stream, it will outline the vessel and demonstrate anatomy.

• Iodine is also filtered by the kidney and can show information about tissue function

Computed Axial TomographyComputed Tomography (CT scan): medical imaging procedure that utilizes computer-processed X-rays to produce tomographic images or 'slices' of specific areas of the body.

It Involves ionizing radiation. The X-ray tube is rotated around the patient and X-rays pass through them and are detected by photomultiplier tubes at the opposite end of the beam. Different tissues absorb or 'attenuate' the X-ray beam by different amounts.

A computer processes the information about the attenuation in each picture element (pixel) into an axial image of the area being examined.

In conventional CT the images are acquired a slice at a time with a slice thickness varying from 2 to 10 mm.

In helical (spiral) CT the image is acquired volumetrically in a continuous movement with no gaps between the slices imaged. This enables the images to be manipulated in different planes and also allows structures to be viewed in three dimensions.

Uses - CT

• Oncology staging

• Trauma assessment

• Guiding biopsies

• Radiotherapy planning

COMPUTED TOMOGRAPHY CT

HIGH ENERGY PHOTON

IONIZING RADIATION

EXPOSES DETECTOR

TOMOGRAPHIC DATA

• In CT scanning, we are able to get slice images or tomographic.

• TOMO=Slice, then Tomography=Slice Imaging• Detectors in the CT scanner count the x-ray

photons that traverse the patient from a rotating x-ray tube and use this data to assign a numerical value (CT number) to the tissue within the patient.

• The computer then assigns a whiteness or blackness to the tissue based on its CT number

LT

Here the yellow line is showing the level where the CT section is made through the upper abdomen at the level of the liver.

Interventional RadiologyInterventional radiology (IR or VIR): a medical sub-specialty of radiology which utilizes minimally-invasive image-guided procedures to diagnose and treat diseases.

Also called angiography or “angio” or “IR” Image formed using broad beam ionizing radiation

(fluoroscopy) Usually involves the use of iodinated contrast agents

and long catheters Many varied techniques including the use of CT or

MRI

Nuclear Medicine

Nuclear medicine: a medical specialty involving the application of radioactive substances in the diagnosis and treatment of disease.

The radioisotopes produce gamma-rays that are emitted by the patient following intravenous injection of the isotope.

The rays are detected by a gamma camera.

Radioisotope investigation allows the assessment of function as well as structure.

The commonest radioisotope used is technetium, which has a half-life of 6 h. Radioisotopes can be tagged with other substances that are selectively taken up by the parts of the body which are being examined.

Common radioisotope investigations

1- Bone scan - Tc phosphonate to look for metastases2- Lung ventilation - Tc DTPA aerosol, krypton gas3- Lung perfusion - Tc micro-aggregate albumin to assess perfusion4- ventilation/perfusion scans for investigation of pulmonary emboli

5- Cardiovascular - thallium scanning to look for cardiac perfusion abnormalities 6- Renal tract - DMSA, DTPA, MAG 3 for assessing renal structure (DMSA) and function (DTPA and MAG 3) 7- Thyroid - iodine or technetium to assess thyroid function/nodules

UltrasoundUltrasound: an oscillating sound pressure wave with a frequency greater than the upper limit of the human hearing range.

Also called “sono” or “echo” or “US” Image formed by transmitting and receiving high

frequency sound waves Image “slices” reconstructed by computation The image formed is related to interfaces between

tissue areas of differing sound transmission characteristics

Image display on computer or multiple films

Ultrasound does not involve ionizing radiation.

It uses the principle of high-frequency sound waves, which when reflected back from structures in the body can be converted into a grey-scale image.

Ultrasound is a real-time examination, which means that a moving image of the body is seen on a screen, as are the scans.

Doppler ultrasound is used to measure blood flow in vascular structures and depends on the principle that there is a shift in reflected sound frequency from flowing blood in vessels.

Advantages

• Non-ionizing (no radiation)• Safe• Can be used to follow up

patients• Images in real-time –

instantaneous• Can be performed at the

bedside• Relatively cheap

Disadvantages

• Difficult in obese patients• Views are often obscured by

air/bowel gas

BASIC ULTRASOUND PHYSICS

Acoustic WindowsDense & elastic structuresLiverSpleen

Fluid-filled structuresHeartUrinary bladder

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Typically the ultrasound probe is placed over areas that transmit the sound best for imaging. These regions are called acoustic windows.

ULTRASOUNDideal for fluid filled structures

Gallbladder

Kidney

Obstetrics

Magnetic Resonance ImagingMagnetic resonance imaging (MRI): a medical imaging technique that uses a magnetic field to visualize internal structures of the body in detail. Also called “MRI” (used to be NMRI) Image formed by transmitting and receiving radio

waves inside a high magnetic field Image “slices” reconstructed by computation The image formed is related to:

Scanner settingsPatient hydrogen densityPatient hydrogen chemical/physical environment

Image display on computer or multiple films

MRI: an imaging modality involves the use of radio-waves and magnetic fields to create an image of the body.

It does not involve ionizing radiation.

The patient is placed in a magnet and a radio-wave applied.

The nuclei of hydrogen atoms in water and fat absorb these waves and emit radiofrequency energy and this can be manipulated by computer to produce an image.

Imaging can be conducted in several planes, e.g. coronal, sagittal and axial.

Imaging depends on the fact that pathological tissues return a different signal to normal tissue and this property is utilized in trying to make a diagnosis from the images.

USES - MRI

• Brain, especially pituitary, posterior fossa• Spinal cord• Musculoskeletal• Abdomen/pelvis• gynecological malignancy• liver

Contra-indications – MRI(Limitations within the MRI room)

• Pacemakers

• Metallic foreign bodies etc

• Claustrophobia

Hydrogen protons in a magnetic field

Radio wave signal transmission

No ionizing radiation

Tomographic data

MAGNETIC RESONANCE

With magnetic resonance, the tissue response to magnetic fields and radio waves serves as the basis for imaging. The images are slices or tomographic and the plane of section can be determined by the machine.

MAGNETIC RESONANCE

EXAMPLES

Brain

Spine

RT

Anterior

Posterior

Anterior

Posterior

Anterior Posterior

Knee

Ionizing Radiation

Radiation causes ionization of atoms and molecules.

Ionization is the underlying mechanism for most radiation detectors and also is responsible for most radiobiological effects.

Biological Effect of Radiation

Why should we protect ourselves from radiation?

Direct molecular absorption of energy

DNA most susceptible

Indirect Action-Radiolysis of Water

Ionization Dissociation

Free Radical Biological Damage

Cause damage to (DNA/RNA) which become non-functional

Somatic Effects

Acute or early (deterministic)within daysdose dependentSeen in accidents and nuclear wars Affects acutely bone marrow, GI tract and skin

and less neurological system. Latent or delayed (stochastic).

not seen for yearscancer, cataract, shortened life span

Principals of Radiation Protection

Time Distance Shielding ALARA (As Low As Reasonably

Achievable)

TIME

• The total radiation exposure to an individual is directly proportional to the time he is exposed to the source.

• Therefore, it is wise to spend no more time than necessary near the source of radiation.

DISTANCE

• The intensity of radiation from a source varies inversely with the square of the distance.

• Therefore, radiation workers should maximize the distance between themselves and the radiation source.

Shielding

• Lead is most commonly used to shield photons in diagnostic imaging.

AngiographyAngiography: a medical imaging technique used to visualize the inside of blood vessels and organs of the body, with particular interest in the arteries, veins and the heart chambers. Real time X-ray study Catheter placed through femoral artery is directed

up aorta into the cerebral vessels. Radio-opaque dye is injected and vessels are

visualized Gold standard for studying cerebral vessels.

Angiography

AP Right ICA Lateral Right ICA

AP Right Vertebral