RAB: Ch. 1 Intro To Medical Imaging

Question 1

Who discovered X-rays

Answer 1

Wilhelm Conrad Roentgen; November 8, 1895

Question 2

Radiography is performed with an x-ray source on one side of the patient and a (typically flat) x-ray detector on the other side. A short-duration (typically less than ½ second) pulse of x-rays is emitted by the ______, a large fraction of the x-rays interact in the patient, and some of the x-rays pass through the patient and reach the detector, where a radiographic image is formed

Answer 2

X-ray tube

Question 3

The homogeneous distribution of x-rays that enters the patient is modified by the degree to which the x-rays are removed from the beam (i.e., attenuated) by ___ and ___ within the tissues

Answer 3

Scattering and absorption

Question 4

The detector used in radiography can be photographic film (e.g., ______ radiography) or an electronic detector system (i.e., ____ radiography).

Answer 4

Screen-film; digital radiography

Question 5

The beginning of diagnostic radiology is represented by this famous radiographic image, made by Roentgen on December 22, 1895 of his wife’s hand (B). The bones of her hand as well as ___ rings on her finger are clearly visible.

Answer 5

Two rings

Question 6

Rrefers to imaging in which the energy source is outside the body on one side, and the energy passes through the body and is detected on the other side of the body

Answer 6

Transmission imaging

Question 7

Refers to the case when each point on the image corresponds to information along a straightline trajectory through the patient

Answer 7

Projection imaging

Question 8

Refers to the continuous acquisition of a sequence of x-ray images over time, essentially a real-time x-ray movie of the patient.

A transmission projection imaging modality, and is, in essence, just real-time radiography.

Use x-ray detector systems capable of producing images in rapid temporal sequence.

Answer 8

Fluoroscopy

Question 9

Uses much lower x-ray energies than general purpose radiography;

Answer 9

Mammography

Question 10

Used for screening asymptomatic women for breast CA.

Used to aid in diagnosis of women with breast symptoms such as presence of a lump.

Answer 10

Screening mammography

Diagnostic mammography

Question 11

Some digital mammography systems are now capable of tomosynthesis, whereby the x-ray tube (and in some cases the detector) moves in an arc from approximately ___ to ___ degrees around the breast. This limited angle tomographic method leads to the reconstruction of tomosynthesis images (Fig. 1-3B), which are _____ to the plane of the detector, and can reduce the superimposition of anatomy above and below the in-focus plane.

Answer 11

7 to 40 degrees;
Parallel

Question 12

Magnetic resonance imaging (MRI) scanners use magnetic fields that are about ____ to _______ times stronger than the earth’s magnetic field. Most MRI utilizes the nuclear magnetic resonance properties of the ____ —that is, the nucleus of the hydrogen atom, which is very abundant in biological tissues (each cubic millimeter of tissue contains about 1018 protons). The proton has a magnetic moment and, when placed in a 1.5 T magnetic field, the proton _____ (wobbles) about its axis and preferentially absorbs radio wave energy at the resonance frequency of about 64 million cycles per second (megahertz—MHz)

Answer 12

10,000 to 60,000 times;
Proton
Precesses (wobbles)
64 million cycles per second

Question 13

In MRI, the patient is placed in the magnetic field, and a pulse of radio waves is generated by _______ (_____) positioned around the patient.

Answer 13

Antennas (“coils”)

Question 14

The protons in the patient absorb the radio waves, and subsequently reemit this radio wave energy after a period of time that depends upon the spatially dependent magnetic properties of the _____. The radio waves emitted by the protons in the patient are detected by the ____ that surround the patient. By slightly changing the strength of the magnetic field as a function of _______ in the patient using magnetic field _______, the proton resonance frequency varies as a function of position, since frequency is proportional to magnetic field strength. The MRI system uses the frequency and phase of the _______ radio waves to determine the position of each signal from the patient. One frequently used mode of operation of MRI systems is referred to as spin echo imaging.

Answer 14

Tissue
Antennas
Position
Gradients
Returning

Question 15

________ energy in the form of high-frequency (“ultra”) sound can be used to generate images of the anatomy of a patient. A short-duration pulse of sound is generated by an ultrasound _______ that is in direct physical contact with the tissues being imaged. The sound waves travel into the tissue, and are ______ by internal structures in the body, creating echoes. The reflected sound waves then reach the ______, which records the returning sound. This mode of operation of an ultrasound device is called _______ imaging.

Answer 15

Mechanical
Transducer
Reflected
Echoes
Transducer
Pulse echo imaging

Question 16

An interface between tissue and ___ is highly echoic, and thus, very little sound can penetrate from tissue into an air-filled cavity. Therefore, ultrasound imaging has less utility in the thorax where the air in the lungs presents a barrier that the sound beam cannot penetrate. Similarly, an interface between tissue and ____ is also highly echoic, thus making brain imaging, for example, impractical in most cases.

Answer 16

Air; bone

Question 17

Doppler ultrasound makes use of a phenomenon familiar to train enthusiasts. For the observer standing beside railroad tracks as a rapidly moving train goes by blowing its whistle, the pitch of the whistle is higher as the train approaches and becomes lower as the train passes by the observer and speeds off into the distance.

The change in the pitch of the whistle, which is an apparent change in the frequency of the sound, is a result of the Doppler ____. The same phenomenon occurs at ultrasound frequencies, and the change in frequency (the Doppler ______) is used to measure the motion of blood

Answer 17

Doppler effect

Doppler shift

Question 18

_______________ is the tomographic counterpart of nuclear medicine planar imaging, just like CT is the tomographic counterpart of radiography.

A nuclear camera records x- or gamma-ray emissions from the patient from a series of different angles around the patient.

These projection data are used to reconstruct a series of tomographic emission images which provide diagnostic functional info. Their tomographic nature allows physicians to better understand the precise distribution of the radioactive agent, and to make a better assessment of the function of specific organs or tissues within the body

Answer 18

Single photon emission computed tomography (SPECT)

Question 19

__________ positively charged electrons, and are emitted by some radioactive isotopes such as fluorine-18 and oxygen-15. These radioisotopes are incorporated into metabolically relevant compounds, such as 18F-fluorodeoxyglucose (18FDG), which localize in the body after administration.

The decay of the isotope produces a positron, which rapidly undergoes a very unique interaction: the positron (e) combines with an electron (e) from the surrounding tissue, and the mass of both the e and the e is converted by annihilation into pure energy, following Einstein’s famous equation E  mc2. The energy that is emitted is called _________ _________.

Answer 19

Positrons

Annihilation radiation

Question 20

Annihilation radiation production is similar to gamma ray emission, except that _____ photons are produced, and they are emitted simultaneously in almost exactly opposite directions, that is, 180 degrees from each other

Answer 20

Two

Question 21

A __________ scanner utilizes rings of detectors that surround the patient, and has special circuitry that is capable of identifying the photon pairs produced during annihilation.

The PET detector system is more sensitive to the presence of radioisotopes than SPECT cameras, and thus can detect very subtle pathologies

Answer 21

positron emission tomography (PET)

Question 22

Manifests as differences in the grayscale values in the image

Answer 22

Contrast

Question 23

The ability to see small detail. An imaging system has higher _____ resolution if it can demonstrate the presence of smaller objects in the image. The limiting _____ resolution is the size of the smallest object that an imaging system can resolve

Answer 23

Spatial resolution