Mid Term Revision

Imaging Procedure 1

Dr Mohamed El Safwany, MD.

Creating the ImageCreating the Image

• ScatterScatter–Creates fogCreates fog

–Lowers contrast (more grays)Lowers contrast (more grays)

• Increases as Increases as

–kV increaseskV increases

–Field size increasesField size increases

–Thickness of part increasesThickness of part increases

Effects of collimation on scatterEffects of collimation on scatter

• Collimate to area Collimate to area of interest -of interest -reduces scatter reduces scatter and radiation and radiation dose to the dose to the patientpatient

GridsGrids

• A device with lead strips that is placed A device with lead strips that is placed between the patient and the cassettebetween the patient and the cassette

• Used on larger body parts to reduce the Used on larger body parts to reduce the number of scattering photons from number of scattering photons from reaching the imagereaching the image

Grid is placedGrid is placedbetween patient (behind table or upright between patient (behind table or upright

bucky) & cassettebucky) & cassetteIf placed BACWARDS CAN CAUSE If placed BACWARDS CAN CAUSE

GRID ERRORSGRID ERRORS

Factors that affect the detail of Factors that affect the detail of an imagean image

SID SID Source to Image DistanceSource to Image Distance

• The greater the distance between the The greater the distance between the source of the x-ray (tube) and the image source of the x-ray (tube) and the image receptor (cassette), the greater the image receptor (cassette), the greater the image sharpness.sharpness.

• Standard distance = 40 in. most examsStandard distance = 40 in. most exams

• Exception = Chest radiography 72 in.Exception = Chest radiography 72 in.

*See page 74 in your book*See page 74 in your book

Shape DistortionShape Distortion

• Misrepresentation of the shape of an Misrepresentation of the shape of an objectobject

• Controlled by alignment of the beam, part Controlled by alignment of the beam, part (object), & image receptor(object), & image receptor

• Influences: Central ray angulation & body Influences: Central ray angulation & body part rotationpart rotation

Bone Classification

• Long

• Flat

• Short

• Irregular

Centers of Endochondral Ossification

• Primary center- midbody or diaphysis

• Secondary center- ends or extremities of the long bones or epiphysis– Epiphyseal plates: found between the

diaphysis and the epiphysis until skeletal growth is complete

Anatomic Position

• Upright, arms adducted, palms forward, head and feet directed straight ahead

• Viewing Radiographs: Display x-rays so that the

patient is facing the viewer in anatomic position

R

Body Planes, Sections and Lines

• Sagittal- any longitudinal plane dividing the body into right and left parts

• Mid-sagittal or median plane- divides the body into equal right and left halves

• Coronal- longitudinal plane dividing the body into anterior and posterior parts

• Mid-coronal- divides the body into equal anterior and posterior parts

• Horizontal or axial plane- transverse plane passing through the body at right angles to the longitudinal plane; divides into superior and inferior portions

• Oblique plane- longitudinal or transverse that is on an angle or slant to the sagittal, coronal or horizontal planes.

Understanding CT and MRI Images

• Longitudinal sections can be taken in sagittal, coronal or oblique planes

• Transverse (axial) or cross sections

Gastrointestional Fluoroscopy

• Esophogram/Barium Swallow

• Modified Barium Swallow/Dysphgiagram

• Upper GI

• Small Bowel Series

• Enteroclysis

• Contrast Enema

• Defecography

Single Contrast vs Double Contrast

• Single Contrast– Generally uses just thin Barium– Distends lumen with high density material– Easier for patient/less mucosal detail

• Double Contrast/Air Contrast– Thick barium coats lumen– Effervescent tablets ingested to distend lumen with air– Produces ‘see-through’ images with greater mucosal

detail – Greater sensitivity for small lesions, polyps, ulcers

Contrast Enemas

• Barium or Gastrograffin

• Double contrast or single contrast

• Generally less sensitive than endoscopy

• Requires bowel prep to assess for mucosal lesions

• Requires some element of patient cooperation

Hysterosalpingogram

• Used to evaluate endometrial canal and fallopian tubes

• Infertility and uterine anomalies

• Dye injected into cervical os under fluoro

• Injection continued with goal to opacify the fallopian tubes and spill contrast into peritoneum

Magnetic Resonance Imaging (MRI)

• Multi-planar scanning• Without ionizing radiation• Images generated using powerful magnets and

pulsed radio waves passing through the body• Data from Pt’s body used to generate image • Field strength of magnets 0.3-3.0 Tesla

MR Contrast Agents• Intravenous contrast---Gadolinium chelate-based

contrast agents

• Gadolinium is a paramagnetic lanthanide that is toxic as a free metal

• Contrast to evaluate BBB, intracranial edema and hemorrhage

• Novel agents being developed as tagged Monoclonal antibodies for Molecular Imaging

MR Applications• Neuro-imaging

-Excellent tool due to high soft tissue contrast resolution

-Abundant water content of CNS allows for imaging soft intracranial tissue

• Head and Neck imaging-Multi-planar capability allows for monitoring extent of

disease

-Differentiating subtle soft tissue boundaries of head and neck

Aims:•Basics

•Best exam results•Appreciate the role radiology plays

Densities The big two densities are:

) 1 (WHITE - Bone

) 2 (BLACK - Air

The others are:

) 3 (DARK GREY- Fat

) 4 (GREY- Soft tissue/water

And if anything Man-made is on the film, it is:

) 5 (BRIGHT WHITE - Man-made

Inspiration/Expiration

Anatomy

Heart (continued)

Lateral CXR (continued)

Heart •Size of heart

•Size of individual

chambers of heart

•Size of pulmonary vessels

•Evidence of stents, clips, wires and valves

•Outline of aorta and IVC and SVC

Typical Mammography Unit

Equipment is C-armSID is fixed at 24 – 26”

Compression Device

Made of firm plastic

Amount of compression: between 25 and 40 pounds pressure

Compression may be uncomfortable!

Digital Mammography

State of the art!

• No film or chemical processing

• Images easily sent over internet

• Much better definition

Routine mammography projections

Craniocaudal (CC)

Mediolateral oblique (MLO)

CT Terminology

• Attenuation is measured in Hounsfield units– Scale -1000 to 1000

• -1000 is air• 0 is water• 1000 is cortical bone

• Attenuation– Hyperattenuating (hyperdense)– Hypoattenuating (hypodense)– Isoattenuating (isodense)

CT Terminology

• What we can see– The brain is grey

• White matter is usually dark grey (40)• Grey matter is usually light grey (45)• CSF is black (0)• Things that are brite on CT

– Bone or calcification (>300)

– Contrast

– Hemorrhage (Acute ~ 70)

– Hypercellular masses

– Metallic foreign bodies

CT Terminology

• Window Width– Number of Hounsfield units from black to

white

• Level or Center– Hounsfield unit approximating mid-gray

CT Terminology

• DICOM– Digital Imaging and Communications in

Medicine– DICOM provides standardized formats for

images, a common information model, application service definitions, and protocols for communication.

Radiation Safety

• Terminology– Gy = Gray is the absorbed dose (SI unit)

• The equivalent of 1 joule/kg of tissue• Rad = radiation absorbed dose

– Sv = Sievert is the dose equivalent (SI unit)• Absorbed dose multiplied by a quality factor• Rem = radiation equivalent man

Radiation Safety

• Effects of X rays.– Absorption of photons by biological

material leads to breakage of chemical bonds.

– The principal biological effect results from damage to DNA caused by either the direct or indirect action of radiation.

Good Luck