Physics and instrumentation

Question 1

A patient scheduled to undergo chemotherapy for BRCA and referred for baseline equilibrium radionuclide angiocardiography (ERNA) for assessment of LV function to monitor for cardiotoxicity. Which of the following is true?
A. ERNA utilized technetium-99m sestamibi to take RBCs
B. Hydralazine, prazosin, heparin, and digoxin improve RBC labeling
C. Heart/lung ratio can be calculated with this technique
D. When calculated LV EF, background activity is added.

Answer 1

C. Heart lung ratio can be calculated with this technique

Question 2

Technetium 99m is used to radiolabel patients RBCs, there are three methods for radiolabeling what are they and describe them?

Answer 2

In vivo- pt receives IV stannous pyrophosphate pertechnetate - fastest and least expensive but has lowest labeling efficiency of the RBCs and has high background due to nonspecific labeling of circulating proteins.
in vitro 10-15ml of tech-99m are added outside the body, the RBCs are reinjected, Ultratag is available and allows for highest labeling efficiency and lowest background activity expensive and time consuming. 3rd in vivitro involves injection of the stannous pyrophosphate prior to removal of 10-15ml of the pt RBCs that are then mixed with tech-99m

Question 3

What common meds inhibit binding of tech-99m pertechnetate to the hgb molecule? How can you tell?

Answer 3

hydralazine prazosin heparin and digoxin -> poor binding is detected by finding free tech-99m pertechnetate in mucosa of the stomach and thyroid gland

Question 4

LVEF calculation?

Answer 4

(Background adjusted end diastolic counts - background adjusted LV counts at end systole)/Background adjusted end diastolic counts

Question 5

Heart lung ration what is it?

Answer 5

Measures how well teh ventricles compensate by comparing counts in heart and lung. Pooling of blood in lungs think HF

Question 6

Assessment of LV and RV using effective radionuclide angiocardiography is what class indication?

Answer 6

CLass 1 by ACC/AHA radionuclide guidelines

Question 7

Which of the following statements regarding first pass radionuclide angiography (FPRNA) is true?
A. FPRNA can detect and quantify left-to-right cardiac shunts
B. Tech-99m diethylaminetriamine pentaacetic acid (DTPA) can be used for FPRNA
C. FPRNA can evaluate right and LV systolic funciton
D. Optimal results are achieved in the upright and straight anterior views
E. Alll of above`

Answer 7

E all of above

Question 8

first pass radionuclide angiography (FPRNA) is used for what?

Answer 8

Measuring LV and RV function, detect and quantify atrial and ventricular shunts

Question 9

diethylaminetriamine pentaacetic acid (DTPA) is cleared by what?

Answer 9

kidneys

Question 10

Tech-99m sulfur colloid cleared by what

Answer 10

liver

Question 11

Tech-99m sestamibi and tetrofosmin when used to assess myocardial perfusion at rest or peak stress ideallly given in what?

Answer 11

small volumes 0.5 to 1ml Bolus

Question 12

first pass radionuclide angiography (FPRNA) can be performed when doing equilibrium radionuclide angiocardiography (ERNA) but by in vivo but not in vitro or in vivitro why?

Answer 12

Large volume administration, need large veins close to heart for rapid bolus of DTPA

Question 13

What view allows for RV and LV assessment

Answer 13

Straight upright anterior view

Question 14

First pass radionuclide angiography allows for RV fxn assessmennt what view is recommended?

Answer 14

right anterior oblique to enhance atrial RV separation

Question 15

Approximately what fraction of 140 keV gamma rays (Tech-99m) pass through a typical low-energy high resolutiorn LEHR ,parallel hole collimator?
A. 1 in 10 (10%)
b. 1 in 100 (1%)
c. 1 in 1,000(0.1%)
D. 1 in 10,000 (0.01%)

Answer 15

D a typical low energy high resolution collimator ahs a sensitivity of around 2000cm/micrCi for tech-99m, which equals (3.3cps)/3.7x10^4 Bq) = 0.9x10^-4cps/Bq. Considering crystal efficiency of about 90% and that the 140 keV emission efficiency of tech-99m is 89%, the collimator efficeincy is 1.1X10^-4 or about 1 in 10,00

Question 16

If a gamma camera wiht parallel hole colllimator is moved farther away from the patient how are resolution and sensitivity affected?
a. resolution worsens and sensitivity remains approximately constant
b. sensitivity worsens, and resolution remains approximately constant
c. both resolution and sensitivity worsen
d. both resolution and sensitivity remain approximately constant

Answer 16

A collimator blur increases wiht distance and thus resolution worsens, the number of coutns passing through the collimator does not change appreciably as distant increases

Question 17

For thallium - 202 imaging, the photons detected in the 70 keV windor are broduced by which mechanism?
A. bremsstrahlung
b. gamma ray emission
c. internal conversion
d. x ray emission

Answer 17

D Thalllium 201 decays by electron capture to mercury -201, mercury - 201 is excited state and releases xr wiht energies near 70kEV

Question 18

In a planar gated blood pool study 121,344 net coutns are measured in the LV at end diastole, and 53,311 net counts are measured at end systole what is lVEF? assume backgroudn count subtraction hasbeen performed

Answer 18

LVEF is end diastole - end systole/ end diastole
(121,344-53,311)/121,344= 56%

Question 19

Which of the following methods of attenuation correction (AC) is not acceptable for nuclear cardiology?
A. transmission source attenuation correction (AC)
B.calculated AC from external boundaries
C. CT based AC
D. none of the choices (all are acceptable)

Answer 19

B. Transmission and CT based AC use a radioactive source or CT to create density or attenuation maps that are applied to the emission activity from the heart during reconstruction. Calculated AC does not directly measure the attenuation but calculates it based on assumptions of uniform aattenuation and has been used successfully for brain SPECT or PET sincee the attenuation coefficient is approximately constant over the entir slice. However, cardiac imaging has large variance in attenuation coefficient (lungs vs diaphragm and breast) and calculated methods are not reliable

Question 20

The frequency of energy peaking for a gamma camera should be performed?
a daily
b. weekly
c. only after camera service
d. monthly

Answer 20

A the gamma camera should be checked each day before use to ensure energy window has not drifted and spectrum is appropriate. the energy spectrum of the radionuclide source is acquired and photopeak is checked to confirm centered in energy window

Question 21

The tech-999m photopeak on a gamma scintillation camera is progressively increasing. The most likely cause for photopeak shift is?
a. high energy collimator
b. energy window set at wrong peak
c. high voltage supply to the photomultiplier tube
d. software issue

Answer 21

C. the PMT consists of a photocathode that is light sensitive and a series of metallic plates dynodes. A high voltage is applied to the plates and when a light photon strikes the crystal the photoelectron is absorbed by the photocathode and is multiplied by each dynode and a pulse is generated which is proportional to the amount of energy of the isotope interacting with the crystal. The voltage has to be very stable and a slight variation will greatly affect he pulse generated

Question 22

To check if PMTs are working proprely on a gamma camera, whcih of the tests should be performed?
a. ceneter of rotation
b. linearity
c. flood field uniformity
d. resolution

Answer 22

C. flood field uniformity - a uniform source of radioactive source (flood sheet) is placed on the camera detector to check if all the PMTs are operational. If a PMT is malfunctioning then a blank spot is observed on the flood scan

Question 23

The intereaction of a tech-99m gamma photon wiht the scintillation camera is primarily by:
a. compton effect
b. photoelectric effect
c. pair production
d. scatter effect

Answer 23

B in photoelectric absorption the gamma ray transfers all its energy to an orbital electron of the absorbing material and a photoelectron is released.

Question 24

what is compton scaatter

Answer 24

occurs when gamma photon transfers only part of its energy to an orbital electron the scattered photon travels in a differenct direction and may further interact in the material

Question 25

The tech-99m peak to be acquired within a 20% window the window setting should be? a. 112 to 168 kev b. 126 to 154 kev c. 0 to 140 kev d. 112 to 140kev

Answer 25

B. tech 99m has a mean photopeak energy of 140kev. a 20% window centered on the photopeak the window width is 140(0.2)=28. This gives a range of 14kev on either side thus 126 to 154

Question 26

The best method to check for patient motion on a cardiac single photon emission CT study is to ? a. use a ramp filter during reconstruction b. review the long and short axis images c. check projection images in a cine format d. ask technologist if patient moved

Answer 26

C this can potentially be fixed by motion correction, however, somtimes requires new study. a ramp filter is routinely used during reconstruction by filtered back projection and does not give any information on motion

Question 27

Motion gives what artifacts?

Answer 27

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

Question 28

In cardiac spect study, the acquired planar projections are first reconstructed into which body plane? a. transaxial b. long axis c. coronal d. planar

Answer 28

A transaxial - 32 to 64 planar projections are acquired 180 degrees around the pt perpendicular to the long axis of the body, and the initial reconstruction is into the transaxial plane. from transaxial plane then the long axis of the heart is defined and subsequently conventional vertical and horizontal long axis and the short axis images are reconstructed

Question 29

In a multigated acquisition (MUGA) study, the caridac cycle is divided in 20 equal time frames, and the pt heart rate is 60 bpm. Avg time per frame is? a. 5s b. 50s c. 0.05s d. 0.5s

Answer 29

C. 60s/(HRx the number of frames) 60/(60x20)=0.05

Question 30

Dual head camera detectors are mounted next to each in a 90 deg orientation to the gantry for a caridac study, this is done why? a. resolution is improved b. time is reduced in half compared to full 180deg rotation c. scatter is reduced. d. resolution is increased

Answer 30

B. in a SPECT study typically 64 projections are obtained over 180 deg at 3 deg increments, and each projection usually takes 20s. a total of ~21mins will be required: with 2 detectors at 90deg orientation time to acquire is half 11 mins

Question 31

The amount of energy deposited by the radiation per unit length in an absorber is known as? a. specific ionization b. linear transfer energy c. range of radiation d. exposure

Answer 31

B. Linear energy transfer (LET) is the amoutn of energy deposited per unit length of the absorber, and units are keV/micrometer. electromagnetic and beta particles have low LET, since they lose little energy per interaction. alpha particles are heavy particles and lose energy very rapidly and have high LET

Question 32

Attenuation artifacts are prevalent in spect imaging modalities. which is true? a. anterior wall attenuation si present in males more than females b. specificity of diagnosing the rca disease is compromised in males c. gated spect images are of little help in ruling out attenuation artifacts d. attenuation artifacts affect sensitivity of spect imaging but not specificty

Answer 32

B. inferior wall attenuation is often present in male patients aka diaphragmatic attenuation and ant attenuation is often in female pts aka breast. normal systolic thickening on gated spect in afixed dfect on both rest and stress images represents an attenuation artifact rather than scar-> reduced systolic thickening

Question 33

Using AC and resolution compensation has been recently introduced in spect imaging. Which is true: a. reduces the sensitivity of spect to detect CAD b. improves the sensitivitiy of spect to detect multivessel cad c. improves the number of false neg spect studies d. reduces the number of false positive spect studies

Answer 33

D. AC significantly improved normalcy rates compared to uncorrected perfusion data using either corrected images or corrected data and quantitative analysis, NO impact on sensitivity, detection of multivessel CAD is reduced

Question 34

WHen comparing pharmacologic spect vs pharmacologic PET all are true except: a. pet has a higher spatial resolution b. pet perfusion tracers have a shorter half-life c. quantification of absolute myocaridal blood flow is more feasible wiht pet d. pet agents are readily and widely available

Answer 34

PET agents used currently for perfusion have limited availability

Question 35

What percentage of 140kev gamma rays tech-99m is attenuated by 10cm of water (attenuation coef of water at 140kev is 0.15cm^-1? a. 22% b 44% c. 56% d. 78%

Answer 35

D. fraction of nonattenuated gamma is e^-(ux), where u is the attenuation coefficient and x is length e^(0.15cm^-1 x 10cm) =0.22 and 1-0.22=78

Question 36

In above situation tech-99m in water the interaction of gamma rays with the medium is dominated by which process? a. photoelectric absorption b. compton scattering c. rayleigh scattering d. pair production

Answer 36

B. Compton scattering dominates. photoelectric absorption is approx proportional to z3/e3 and is negligible at 140kev for a low-z material like water. fRayleigh scattering is not significant at photon energies used in nuc med. Pair production requires photon energies of at least 1.0MeV = 2x511keV

Question 37

Cardiac spect cameras currently utilize any of the following collimation methods except a. parallel hole b. converging c. diverging d. pinhole

Answer 37

C diverging - nearly all spect camera use parallel hole collimation. some new design use converging such as fan beam, cone beam, or cardiofocal. Coverging collimation is better because the heart is projected over a large area of the detector providing higher sensitivity than parallel hole collimation. Another new design is multipinhole collimation where severeal miniature detectors each having pinhole collimator are arranged so that all pinholes are focused on the heart. higher sensitivity and resolution are possible wiht this. diverging is not really used.

Question 38

Some solid state cameras use photoiodes coupled to pixelated scintillation crystals. What is a mian advantage of this design, compared to conventional gamma cameras having a large - area scintillation crystal wiht photomultiplier tubes? a. higher sensitivity b. higher energy resolution c. higher spatial resolution d. compact size and lower weight

Answer 38

D. PMTs are several inches long and as a result a gamma camera is about a foot or more in depth and is HEAVY (thick lead shielding). solid state photodiodes are very thin. they are thin and lightweight and can be used in small cameras suitable for cardiac imaging. sensitivity is governed mainly by collimator design as long as sufficient thickness to absorb photons, energy resolution is comparably or a bit worse, spatial resolution depends ono collimator design, resolution is comparable

Question 39

Other solid state detectors use semiconductor crystals such as cadmium zinc telluride (CZT), instead of scintillation crystals. What is a main advantage of semiconductor crystals compared to conventional gamma cameras having a large area scintillation crystal with PMT? a. hgiher sensitivity b. higher energy res c. higher spatial res d. lower cost

Answer 39

B. Higher energy res, in semiconductor solid state detector electrons produced by absorption of an emission photon are amplified and detected directly. this is much more efficient compared to a scintillation dtector which involves several steps; conversion of electrons to scintillation photons, transport of scintillation photons to the PMTs, conversion of scintillation photons into electrons in the photocathodes of the PMTs, and amplification and detection of electrons in the PMTs. The detected electrons in the solid state detector have better statistical accuracy, and the energy resolution is higher. sensitivity is governed mailny by the collimator design, assuming the crystal has sfufficient thickness to absorb most emissions photons. The intrinsic spatial resolution of a semiconductor solid state detector is often better than that of conventional gamm camera, extrinsic spatial resolution depends mainly on the collimator design. The cost per unit area of semiconductor solid state detectors i smuch higher htan that of a conventional gamma camera. thus solid state detectors are only practical with clever camera designs using small area detectors such as multipinhole collimation or multiple pivoting small detectors.

Question 40

All of the following are challenges associated with PET/MR for cardiac imaging except: a. pet resolution and sensitivity b. accuracy of pet attenuation correction c. mri safety assoc with cardiac implants d. mri safety assoc with radiopharmaceutical administration

Answer 40

A. PET resolution and sensitivity for pet/mr are comparable to pet/ct. Bone can cause large photopenic regions in MRI images and cause significant errors in pet attenuation correction

Question 41

Modern PET scanners can acquire raw data in list mode, as opposed to sinograms. All of the following are advantages of list mode acquisition except: a. higher count statistics b. retrospective ecg or respiratory gating c. troubleshooting patient motion d. smaller data files

Answer 41

A. in list mode acquisition the location and timing of each event is stored in a list. gated and dynamic studies are stored more efficiently in list mode resulting in smaller data files. studies can be retrospectiviely processed with different gating parameters or different timing of dynamic sequencys. List mode does not hcange the sensitivity of the camera or increase number of counts required.

Question 42

In the past spect and pet images were reconstructed using filtered backprojection algorithm. recently iterative reconstruction has become common. in advanced implementation of iterative reconstruction the blur in the raw data associated iwht the detector and collimator is modeled. this method has all of the following advantages except: A. better image quality b. potential for lower radiation dose c. need to acquire only half the projections d. ability to recover from spatial resolution.

Answer 42

C. modeling the scanner's inherent resolution (aka point spread function) spatial resolution is enhanced. with equal scan time and injected dose, image quality has been shown to improve when using the more accurate model of the system. similar image quality may be attained with fewer coutns, sometimes advertised as half-time imaging. One approach is to reduce injected activity reducing radiation dose to the patient. another is to reduce scan time -> improve throughput -> minimize patient motion and should improve quality.

Question 43

When using iterative reconstruction the number of iterations is specified for stopping the program. why is this done? a. to prevent impractical computation time b. to control excessive image noise c. optimize spatial resolution d. math number of projections (equal to iterations x subsets)

Answer 43

B. sufficient number of iterations is necessary to ensure convergence and accuracy. however large number of iterations amplifies noise. number of iterations is divisible by the number of subsets.

Question 44

For cardiac PET acquired wiht a pet/ct why is it important to control the respiratory phase of the CT porition of the exam? a. resp phase affects the yocardial distribution of the fdg b. resp phase affects myocardial distribution of the perfusion tracer c. resp phase affects pet attenuation correction data d. resp phase affects scatter in the pet data

Answer 44

C. tradition dedicated pet scanners acquire transmission attenuation data under free breathing conditions so anatomy of the attenuation map mathches that of the pet data. pet/ct images are acquired rapidly and the annatomy of the ct images corrresponds to a specific respiratory phase as the beam passes each slice and may not match the anatomy of the pet data. under free breathing PET most of data is acquired at end expiration. if lungs are inflated in CT images position of the heart shifts relative to pet data. lateral wall of the myocaridum in the ct images corresponds to the lung region of the pet data, and cna result in ct based attenuation correction underestimates the attenuation of the pet lateral wall and cause a significant artifactual defect. CT AC should be acquired at or near end expiration

Question 45

Which method of cardiac pet attenuation correction is not susceptible to artifact from metallic implants? a. transmission attenuation correction b. ct based attenuation correction c. mr based AC d. all are not affected by metallic implants

Answer 45

A. PET photons have high energy 511kev and interact with all materials predominantly by Compton scattering. Transmission imaging wiht external sources involves photons with the same or similar energy and athe measurement of attenuation is accurate for pet attenuation correction for both body tissue and metallic implants. CT photons have much lower energy mostly 40-100keV. These lower energy photons interact iwht soft tissue primarily by Compton scattering, however with metallic implants by photoelecctric absorption and are much more strongly absorbed. CT image significantly overestimates teh attenuation of metallic implants. THe CT image is used for PET attenuation correction, it overcorrects for attenuation and could result in artificially high uptake near the implant.

Question 46

A cardiac imaging department w/o access to N13 ammonia or a Rubidium generator, wishes to perform a rest/stress tech-99m spect study in addition to a viability fdg pet study. In which order should these studies be scheduled? a. first fdg pet study then rest/stress spect b. first rest/stress spect and then fdg pet c. perform fdg pet in between the rest and stress spect d. order don't matter

Answer 46

Spect collimators are low energy collimators are designed to colliate 140kev photons. high energy photons from F18 easily penetrate the collimator and contribute excessive background counts in the spect images. A PET scanner operates in coincidence mode and only counts events when two 511kev photons are detected simultaneously. single photons from tech-99m decay are not counted. Thus SPECT should be first and then PET given PET will count only 511 kev photons and spect cameras would have excess background counts in the spect images.