Nuclear - Physics Flashcards

Question

How can AC SPECT MPI be obtained in absence of a CT?

Answer 1

* applying attenuation correction requires a **transmission scan** * this scan contains the **tissue attenuation** and is also known as the **attenuation map** * such a scan can be obtained with a **line-source** using the same SPECT detectors * but can also be obtained - in a better quality - with a low-dose CT scan

Answer 2

**O-15** * beta-positive or positron emitter used as O-15 water to measure myocardial blood flow in cardiac PET

Answer 3

**O-15** * O-15 is a beta-positive or positron emitter used as O-15-water to measure myocardial blood flow in cardiac PET * not FDA approved, used in research in Europe

Answer 4

* alpha emitter * the Ra-223 decay chain will also emit beta-negative particles, but these are irrelevant for cardiac imaging * used in treatment of castration resistant prostate cancer with bone metastasis

Answer 5

**The physical half-life of Rb-82 is too short for transport from offsite** * 75 second half-life of Rb-82 means that in under 12.5 minutes (10 half-lives), there will be less than one-thousandth ( \< 1/1000) of the original activity left * Rb-82 is generated onsite from a Sr-82-/Rb-82 generator

Answer 6

**Annihilation photons in PET cannot be discriminated by energy windowing** * the signal in PET is carried by the annihilation photons which all have an energy of 511 keV, regardless of the radiotracer * radiotracer discrimination, based on discrimination of separate energy windows for the detected photons, cannot be used * Two data sets can be constructed based on energy discrimination * Because of the need for photon energy discrimination, the higher energy resolution provided by solid state CZTdedicated cardiac cameras has the potential of facilitating sumultaneous dual isotope imaging

Answer 7

**positively charged electron** * a nucleus with too many protons is unstable * a proton in the nuclus is transformed into a neutron * and a positively charged electron and a neutrino are ejected from the nucleus

Answer 8

* **positron combines with the negative electron** --\> annihilation reaction * massess are converted to energy * **mass-energy equivalent = 511 keV (two annihilation photons)** * photons leave the site of the event in nearly exact opposite directions **(180 degrees apart)**

Answer 9

**Use CZT technology with iterative reconstruction techniques** * can improve image quality through noise reduction and therefore allow a reduction in acquisition time and/or administered activity

Answer 10

* amount of photon counts (mainly determines scan quality) * scan time and activity are interchangeable

Answer 11

* increase amount of photon counts But * decrease the intrinsic **resolution** and **quality**

Answer 12

**No, the down-scatter of photons from Tc-99m into the lower TI-201 energy window will degrade the image** * without sophisticated algorithms to remove the high degree of cross talk, the TI-201 scan should be acquired on another visit

Answer 13

* Tc-99m --\> 6.01 h * TI-201 --\> 73.1 h

Answer 14

**The greater the scattering angle, the less energy the scattered photon has** * scattered photons degrade image quality * the lower energy limit of the imaging peak (typically 126 keV for the 140 keV Tc-99m peak) is set to reject many of these scatered photons: * ideally this would reject photons scattered through angles greater than 53 degrees

Answer 15

**A narrow energy window setting** * it is possible to discriminate against scattered photons by using pulse-height analyzer window (PHA) or energy window

Answer 16

* Renal - 27% * Fecal - 33% \*\*\*at 48 hours after injection

Answer 17

**Increased attenuation** * photon attenuation is much higher for tissue than air, more photons are attenuated in heavier patients * this effect (up to a certain range) can be compensated by a higher activity --\> number of detected photons remains the same

Answer 18

Pulse Height Analyzer (PHA) or Energy Window

Answer 19

**B - annihilation event** * annihilation event in which two photons are emitted in opposing directions * however, one of them is scattered and its direction is slightly changed * both photons are still detected within the set window time and recognized as a photon pair * However, the line of response is not correct: **a scatter coincidence**

Answer 20

* A * shows a **true event** in which the line of coincidence (blue line) passes through the point of annihilation

Answer 21

* B * annihilation event in which two photons are emitted in opposing dirrections * scatter coincidence

Answer 22

* C * two events but as they are not in opposite site of the scanner, they are not recognized as an event

Answer 23

* D * Random effect in which two separate events are recognized as one event

Answer 24

* E * Annihilation but one photon does not reach the detector due to attenuation and this event is therefore not registered

Answer 25

**15 mm** * the original shielding contains 3 half value layers (HVL) * 50% of the radiation is attenuated per HVL * to obtain total transmission of 12.5% (or shielding of 87.5%) will need 3 HVLs * 3 HVL's (to produced 12.5% total transmission) x 5 mm = * **15 mm**

Answer 26

**The scan quality will be lower due to increased scatter** * increase in scatter cannot be compensated by either an increase in activity or scan time, or by altering the energy acceptance window and will therefore negatively impact the image quality

Answer 27

**Collimator hole geometry** * resolution recovery models the collimator hole length and width to correct for: * distance dependent blurring * loss of resolution

Answer 28

**15%** (130 to 150 keV) or **20%** (126 to 154 keV)

Answer 29

**Decrease the size and severity of stress perfusion defects** * as the cutoff frequency is lowered, more high frequency data are eliminated from the reconstructed SPECT image * lowering the cutoff frequency --\> high frequency noise and also the sharpness and severity of discrete perfusion defects are decreased

Answer 30

* gamma ray photon interacts with electrons in body and loses a part of its energy to an electron * with reduced energy, compton-scattered photon is deflected from its original path * photons scattered by a large angle have lower energy * can discriminate against them using PHA or energy window

Answer 31

**Increased tissue layer --\> increased scatter**

Answer 32

when high energy photons result in septal penetration and further loss of resolution

Answer 33

* **resolution recovery** * iterative reconstruction * noise reduction/modulation

Answer 34

solid-state CZT dedicated cardiac SPECT devices * current solid-state CZT dedicated cardiac SPECT devices use stationary gantries * COR is irrelevant to gantries that do not rotate during acquisition

Answer 35

**a wobble in a loose detector head having potentially fatal clinical consequences** * would precede most catastrophic mechanical failures (rare crush injuries) * would contribute greatly to the misalignment detected by COR

Answer 36

* determines if the heads of the system are aligned to the center of the field-of-view being imaged * point source in the center of the field-of-view (FOV) should remain in the center of the projection data given by each head * in unaligned systems, the projection of the point will drift as the heads rotate * Correction: * hardware * reconstruction software

Answer 37

**less effective for radionuclides with a high photon energy** * the attenuaton coefficient decreases for photons with higher energy * collimators with higher septal thickness are then required --\> limit the efficiency of the collimator

Answer 38

* fraction of photons (Y rays) passing through the collimator per emitted photon by the source--\> that actually project the Y-ray image onto the detector * decreases for a larger hole length --\> as less photons pass through the collimator * typically only a few percent or less

Answer 39

* increasing **length of a collimator** by a factor of 2 --\> * **efficiency will decrease** by a factor of more than 4

Answer 40

decreases linearly with decreasing diameter

Answer 41

improves intrinsic resolution

Answer 42

* filters noise * contributes greatly to "signal-to-noise" ratio

Answer 43

**increased number of detectors** * increased number of individual detectors - 19 detector modules (all consisting of) * 32x32 detectors * small pixel size (2.46x2.46mm) * negligible crosstalk

Answer 44

* positron range * non-colinearity * detector element size * pixel size in reconstructed images

Answer 45

affects the performance of a scintillation camera at high count rates

Answer 46

solid-state detectors offer **better energy resoltuion** with **high detection efficiency** * they use silicon diodes instead of PMT's

Answer 47

**straight upright anterior view** * has the advantage of stabilizing the patient's chest against the detector and positioning the patient so that the right and left ventricles will be in the field of view **shallow RAO view** * enhances right atrial-RV separation

Answer 48

* measure LV and RV function * quantify atrial and ventricular shunts

Answer 49

**1 in 10,000 (0.01%)** * typical LEHR collimatory has a sensitivity of around 200 cpm/μCi for technetium-99m, which equals (3.3 cps)/3.7x10⁴ Bq) = 0.9 x 10 ^-4

Answer 50

**Resolution worsens, sensitivity remains approximately constant** * collimator blur increases with distance --\> decreased resolution * number of counts passing through the collimator does not change appreciably as distance increases

Answer 51

**X-ray emission** * Tl-201 decays by electron capture to mercury-201 * mercury-201 is in an excited state and releases **x-rays with energies near 70keV**

Answer 52

* Transmission source AC * CT-based AC

Answer 53

**calculated AC from external boundaries** * does not directly measure * calculates based on assumptions of uniform attenuation * used successfully for brain SPECT or PET since attenuation coefficient is approximately constant over the entire slice * cardiac imaging has a **large variance in attenuation coefficient** (lungs vs. other tissues such as diaphragm and breast) --\> making calculated method unreliable

Answer 54

**Daily** * should be checked each day before use * to be sure the energy window has not drifted and * energy spectrum is of the appropriate shape * Energy specturm of a radionuclide source is acquired --\> photopeak is checked (either automatically or visually) to confirm that it is centered in the energy window

Answer 55

**High-voltage supply to the photomultiplier tube (PMT)** * PMT consists of a photocathode that is light sensitive and a series of metallic plates (dynodes) * high voltage is applied to the plates --\> when a light photon strikes the crystal --\> the photoelectron is absorbed by the photocathode --\> multiplied by each dynode --\> pulse is generated, which is proportional to the amount of energy of the isotope interacting with the crystal * voltage to these plates has to be very stable, and a slight variation will greatly affect the pulse generated

Answer 56

**Flood-field uniformity** * a uniform source/radioactive source (flood sheet) is placed on the camera detector to check if all the PMTs are operational * if a PMT tube is malfunctioning, then a blank spot is observed on the flood scan * Large white area shows the abnormality, the rest of the detector is uniform

Answer 57

* Energy peaking - **daily** * Uniformity test - **daily** * Linearity and resolution - **weekly** * Sensitivity test - **weekly**

Answer 58

verifying that the pulse height analyser's energy window is over the photopeak energy

Answer 59

* 5 UFOV's (universal field of view's) from the uncollimated camera with a point source * sheet source (Cobalt 57) with collimated camera

Answer 60

**photoelectric effect** * gamma ray transfers **all of its energy** to an orbital electron of the absorbing material and a photoelectron is released \*\*\*\*Compton scatter --\> occurs when the gamma photon transfers only part of its energy

Answer 61

**126 keV - 154 keV**

Answer 62

**check projection images in a cine format**

Answer 63

* misalignment of the apex * matching 180-degree areas of decreased intensity in the anterior and inferior walls * hotspots in the septum or lateral wall * "blobs" or a ring of activity in the anterior wall or an "apical nipple"

Answer 64

**Transaxial**

Answer 65

**0.05 seconds** * 60 s / (HR x number of frames) * 60 / (60 x 20) = 0.05s

Answer 66

**the time is reduced in half compared to full 180-degree rotation** * typically 64 projections are obtained over 180 degrees at 3-degree increments, and each projection usually takes about 20s --\> 21 minutes total required * If 2 detectors at 90-degree orientation are used, the time to acquire 64 projection will be half --\> 11 minutes

Answer 67

amount of energy deposited per unit length of the absorber * units are expressed as keV/μm

Answer 68

* electromagnetic and beta particles --\> **low LET** * lose little energy per interaction * alpha particles --\> **high LET** * heavy particles and lose energy very rapidly

Answer 69

* males --\> **diaphragmatic (inferior) attenuation** * females --\> **breast (anterior) attenuation**

Answer 70

**Reduces the number of false-positive SPECT studies** * AC significantly improved the normalcy rate compared to uncorrected perfusion data using either the corrected images (96% vs. 86%) or the corrected data and quantitative analysis (97% vs. 86%) * No impact on sensitivity

Answer 71

**PET agents (Rb-82 and N-13) have limited availability**

Answer 72

* **78%** * **Compton scattering**

Answer 73

* Parallel-hole collimation * Converging collimation * fan-beam, cone-beam, cardiofocal * Pinhole collimation \*\*\*\*\***Diverging collimation no longer used**

Answer 74

**Compact size and lower weight** * PMTs are several inches long and much larger/heavier than solid-state photodiodes

Answer 75

* Accuracy of PET AC * MRI safety associated with cardiac implants * MRI safety associated with radiopharmaceutical administration

Answer 76

* Retrospective EKG or respiratory gating * Troubleshooting patient motion * Smaller data files (gated and dynamic studies) **\*\*\*higher count statistics - no effect on the sensitivity of the camera or number of counts**

Answer 77

* better image quality * potential for lower radiation dose * ability to recover some spatial resolution * by modeling the scanner's inherent resolution (aka point spread function) --\> spatial resolution is enhanced (to some degree) **\*\*\*need to acquire only half the projections**

Answer 78

**to control excessive image noise** * a sufficient number of iterations is necessary to ensure convergence and accuracy * however, a large number of iterations --\> amplifies noise * typical clinical protocol * specifies an optimal number of iterations to limit noise * while ensuring accuracy * along with a filter to smooth out fluctuations in the reconstructed images

Answer 79

**the respiratory phase affects PET attenuation correction** * important during CT-AC acquisition to ensure that the respiratory phase is near end expiration to best match the anatomy of the free-breathing PET scan * if lungs are inflated in the CT images, the position of the heart shifts relative to the PET data

Answer 80

**Transmission attenuation correction (using external Ge68 or Cs137 sources)** * transmission imaging with external sources involves photons with the same or similar energy, and the measurement of attenuation is accurate for PET attenuation correction for both body tissue and metallic implants * CT photons have much lower energy (40-100 keV range) and interact with metallic implants primarily by photoelectric absorption and are much more strongly absorbed

Answer 81

**First perform rest/stress Tc-99m SPECT --\> F18-FDG PET study** * Tc-99m SPECT collimators are designated as "low-energy collimators" --\> collimate 140keV photons * F18-FDG PET requires "high-energy" photons (511 keV) that would easily penetrate the collimator and contribute excessive background counts

Nuclear - Physics Flashcards

(106 cards)