(8/26/10) - Intro to Imaging

Types of Imaging
1. Identify the energy source used to obtain images of the body in each of the four primary imaging modalities in use today (radiography, computed tomography, magnetic resonance and ultrasound).

*Radiography – X-rays

*Computed Tomography – X-rays

*Magnetic resonance – radio frequency transmitter – creating magnetic field

*Ultrasound – mechanical pressure wave

Common Views
2. Identify the common views of the body obtained in radiography (CXR). Distinguish a PA from an AP projection in terms of how they are obtained. Identify which of these views is preferred.

The common views are posteroanterior (PA), anteroposterior (AP), lateral, oblique. In PA the xray travels from the back to the front, whereas in AP it travels from the front to the back. Appearences of both are similar. Lateral comes in from the side. PA preferred over AP.

Orthogonal Radiographs
3. Indicate why it is necessary in some instances to obtain two orthogonal radiographs of the 3-dimensional human body.

Two orthogonal radiographs allow for a more precise localization of placement in the body of a point of interest as one radiograph only gives you a two-dimensional view. ==

Tissue Density and Appearance
4. Describe the effect of tissue density on X-ray absorption and identify the typical appearance of the following tissues on a radiograph: air, fat, water, and metal or bone.

The denser a material, the more of X-ray that is absorbed, and the less that shines through. Air and fat both appear black, although air is a little more black. Water (tissues, muscles) appear different shades of gray. Metal and bone appear white.

Contrast
5. Identify the general purpose of contrast media. Distinguish the uses of iodinated contrast in CT and of barium in gastrointestinal imaging.

Contrast media is used to distinguish between normal and abnormal tissues, to define vascular anatomy, and to improve visualization of some organs. There is varying degree of uptake of the contrast in different types of tissues, and the more contrast a tissue takes up, the whiter it appears. Iodinated contrast used in CT is often injected right into the vasculature (for angiography) and makes the vasculature really defined. Quick acting. Some oral tablets can be given to visualize the gall bladder. The barium for GI imaging is given orally. It defines the mucosal pattern very well.

6. Identify the contraindications for iodinated contrast on CT. Iodinated contrast should not be used for patients in renal dysfunction, hypersensitivity, diabetes, and vascular disease. (Even the low osmolar ones).

Planes of Section in CT Images
7. List the planes of section that can be viewed with computed tomography and be able to identify these planes of section in CT images.

*Axial or transverse – horizontal slices

*Sagittal – slice from posterior to anterior

*Coronal – lateral slice

Image Densities in CT
8. Compare the image densities obtained in CT with those obtained in CXR.

They are the same because both technologies use x-rays.

Common Indications for CT
9. Identify common indications for CT.

CT shows slices of anatomical structure, which CXR shows the entire anatomical structure. CT also captures its information in such a way that the output is digital, which allows for ease of communication of the information.

From table 1.2 (pg 7), common indications for CT imaging: trauma, suspected/known intracranial hemorrhage, abdominal injury, fracture detection/ evaluation, spine alignment, detection of foreign bodie (esp. joints), diagnosis of primary and secondary neoplasms, tumor staging

Plane of Sections in MRI
10 Identify the plane of sections that can be obtained using magnetic resonance (MR).

MR can be used to obtain coronal, sagittal, or axial images, although it is better than CT at coronal and Sagittal, while CT is better at axial images.

What's Best For Soft Tissue Contrast?
11. Rank, in order from best to least, the ability of MR, CT and CXR to provide soft tissue contrast.

MRI, CT (because we can use contrast), CXR

Disadvantages and Contraindictions for MRI
12. Identify the disadvantages and contraindications for MRI.


 * Disadvantages: More expensive than CT, Long scan times may result in claustrophobia and motion artifacts, limited availability


 * Contraindications: Pregnancy (unless absolute emergency), cerebral aneurysms clipped by ferromagnetic clips, cardiac pacemakers, inner ear implants, metallic foreign bodies in and around the eyes.

Hydrogen Atoms and Proton Density in MRI
13. Describe the effect of hydrogen atoms and proton density resulting images in MRI.

Hydrogen atoms have single positive charge and spin, and as result have little magnetic fields surrounding each of them. When MRI transmits radio frequency, creating a magnetic field, the hydrogen atoms become excited and align themselves to the big field. Upon elimination of the big field, the H atoms drop back to their ground state and release energy which is received by MRI machine and translated to picture.

T1- and T2-weighted MRI
14. Distinguish the appearance of fat and water in T1- and T2-weighted (T2W) magnetic resonance images. Be able to distinguish T1W from T2W images.

In T1 images fat appears white and water (in tissues) is a detailed gray. In T2 images water appears to be a lighter gray and fat appears gray.

15. Distinguish the different uses of T1W- and T2W MR imaging.

T1 images used when seeking anatomical information because they provide better resolution. T2 images used when seeking certain pathologies because they provide better contrast. (because T2 causes water to light up to a greater extent).

Ultrasound
16. Identify the entity received by an ultrasound transducer and how images are generated. What two types of tissue are not well visualized with US?

The transducer in a US machine emits high frequency sound waves (1 to 10 MHz) which go into the tissue and depending on the differences in densities between to tissues may be reflected back to the transducer. Based on signals received image can be formed. Two types of tissue not visualized well with US are bone and lung tissue.

Common Uses of US imaging
17. Identify the common uses of US imaging, its advantages and disadvantages.

*Common uses: obstetrics, pediatric brain, testicle and prostate, female pelvis, chest for flexural fluid drainage, abdomen (kidney, pancreas, liver, and gallbladder), vascular disease, rotator cuff of the shoulder

*Advantages: multiple plane imaging including obliques, safe – no known biological harm at diagnostic sound frequency levels, painless (noninvasive), inexpensive, equipment cost is less than CT and MRI, real time or cine is possible, portable

Disadvantages: requires technical skill of operator, not good for bone and lung imaging

Least to most harmful to patient
19. Rank, in order from least to potentially most harmful to the patient: MRI, CT, CXR and US.

US, MRI, CXR, CT (not sure about order of CXR and CT, just guessed CT most harmful because a CT study takes more time) //CT is definitely more harmful because it is equal to 3 years of background radiation exposure, whereas CXR is equal to only a few days\\

Be able to recognize...
18. Be able to distinguish CT, MR and US images.

·     Fat: CT: black; T1 MRI: white; T2 MRI: light gray''' '''

·     Muscles: CT: gray, MRI: black''' '''

·     Bone cortex: CT: white, MRI: dark''' '''

·     Bone marrow: CT: gray, MRI: dark''' '''

20. Be able to differentiate between the right and left sides of the body in CXR and CT. Be able to identify anterior and posterior surfaces of the body in sagittal CT images.
 * Patient is facing you (so your left is their right)
 * For sagittal images, left is anterior; right is posterior

21. Be able to recognize barium on GI studies, and intravenous contrast in CT and MRI.
 * will look very bright

22. Name the imaging modality of choice for pregnant patients.
 * Usually US (maybe MRI); CT is used only when it is an emergency (MRI takes a long time)