L 11: TP II pt data acquisition, treatment verification and corrections Flashcards
1
Q
Patient data that is needed
A
- Body contour outline
- Density of the internal structure
- Location
- Extent of the target volume
2
Q
CT, Housfield number formula
A
- Hounsfield unit represents a change of 0.1% in the attenuation coefficient of water.
- The Hounsfield numbers for most tissues are close to 0,
and approximately ** +1,000 for bone ** - CT numbers bear a linear relationship with attenuation coefficients.
*
3
Q
Ultrasound
A
- An ultrasound (or ultrasonic) wave is a sound wave having a frequency greater than 20,000 cycles per second or hertz (Hz).
- Ultrasound waves of frequencies 1 to 20 MHz are used in diagnostic radiology.
- The larger the difference in Z between the two media, the greater is the fraction of ultrasound energy reflected at the interface. For example, strong reflections of ultrasound occur at the air–tissue, tissue–bone, and chest wall–lung interfaces due to high impedance mismatch.
4
Q
PET-CT
A
- FDG is an analog of glucose that accumulates in metabolically active cells.
- When the positron is emitted by F18, it annihilates a nearby electron, with the emission of two 0.511-MeV photons in opposite directions.
- From the detection of these photons, computer software (e.g., filtered back-projection algorithm) reconstructs the site of the annihilation events
and the intervening anatomy.
5
Q
MRI
A
- MRI can be used to scan directly in axial, sagittal, coronal, or oblique planes.
- Other advantages over CT include not involving the use of ionizing radiation, higher contrast, and better imaging of soft tissue tumors.
- Some disadvantages compared with CT include lower spatial resolution; inability to image bone or calcifications, motion artifacts, longer scan acquisition time, interference with metallic objects.
- It is a resonance transition between nuclear spin states of certain atomic nuclei when subjected to a radiofrequency (RF) signal of a specific frequency in the presence of an external magnetic field.
6
Q
Tissue compensation
A
- Compensators are used to compensate for missing tissue at the surface or internal inhomogeneities such as lung. Their design takes into account the extent of missing tissue, compensator to surface distance (or thickness ratio), and the density of the compensator material.
