PET scan in cardiac imaging by Dr. Crystal KC

1. PET SCAN IN CARDIAC IMAGING
DR Crystal K C
2nd year Resident
MD Radiodiagnosis

2. Introduction
• Positron emission tomography (PET) is a
modern non-invasive imaging technique for
quantification of radioactivity in vivo.
• It involves the intravenous injection of a
positron-emitting radiopharmaceutical,
waiting to allow for systemic distribution, and
then scanning to detect and quantification of
patterns of radiopharmaceutical accumulation
in the body.

3. BASICS
• Positron Emission:
• Positron(e+ ) is the antimatter particle of the
electron(e_ ).
• Is emitted from the radionuclides such as F-
18, carbon-11 and oxygen -15.
• Most commonly used is the isotope of
fluorine.

4. Fluorine
• Atomic number: 9
• Electrons 2+7
• Proton: 9
• Neutrons: 10
• Nucleons : 10+9= 19
• 19
9F is stable.
• Isotopes: 18
9F – Is commonly used
radioisotope.

5. Decay of18
9F
•18
9F Decay
18
8O + e+

6. • O-18 and F-18 are isobars, that is, they have
the same mass number (A nucleons) but
different atomic numbers
• Z is 8 for oxygen and 9 for fluorine.
• F-18 is an unstable radioisotope and has a
half-life of 109 minutes.
• It decays by beta-plus emission or electron
capture and emits a neutrino and a positron.

7. Annihilation
Figure 1. Annihilation
reaction.
Positrons released
from the nucleus of
FDG annihilate with
electrons , releasing
two coincidence 511-
keV photons , which
are detected by
scintillation crystals
(blue rectangles).
N neutron, P proton.

8. Production of F-18
Figure 2. Production of F-18. After
acceleration in a cyclotron, negatively
charged hydrogen ions (red and blue
spheres) pass through a carbon foil in a
carousel, which removes the electrons
(blue spheres) from the hydrogen ion,
leaving behind high-energy protons (red
spheres). The protons are directed toward
a target chamber that contains stable O-
18–enriched water, thus producing
hydrogen (F-18) fluoride.

9. •H2(O-18) +H-1 +
energy H2(F-18).

10. • Typically, 0.3 mL of O-18–enriched water in a
silver container (called a slug) is the target for
production of 400–500 mCi of F-18 under
standard conditions by using the cyclotron.
• This process takes approximately 20 minutes.
• By varying the amount of O-18–enriched
water in the slug, larger quantities of F-18
fluoride can be produced.

11. Synthesis of FDG
• Bombarding O-18–enriched water with
protons in the cyclotron results in a mixture of
H2(F-18) and O-18–enriched water.
• Synthesis of FDG from this mixture is an
automated computer-controlled
radiochemical process that takes
approximately 50 minutes to complete.
• The FDG thus produced is a sterile, non
pyrogenic, colorless, and clear liquid.

12. Tumor Physiology and FDG uptake

13. Detection of Emission
• A positron is a positively charged electron
with the same mass as an electron that
annihilates with an electron within
milliseconds of its emission
• Release two photons (511 keV) moving in
opposite directions.
• These annihilation photons, and not
positrons, are detected during PET.

14. • The detectors in PET scanners are scintillation
crystals coupled to photomultiplier tubes
(PMTs).
• Compared with most radioisotopes used in
nuclear medicine, the radionuclides in PET
emit photons of much higher energies (511
keV for FDG vs 140 keV for technetium-99m).
• Hence, detectors with much higher stopping
power are required.

15. Figure : Photograph (frontal view) of a hybrid PET-CT
scanner shows the PET ring detector system (red ring). There
are up to 250 block detectors in the ring. Drawing shows a
detector block with 8x8 smaller scintillation crystals (green
and orange rectangles) linked to four photomultiplier tubes
(blue circles).

16. PET Detectors
Cerium doped Lutetium oxyorthosilicate (LSO)
o Emits five fold as much light as BGO crystals.
o Decay time for LSO is lower at 40 nsec (300nsec)
o This enables the necessary counts or scintillation
events required for image formation to be obtained
in less time when LSO crystals are used, thereby
significantly decreasing the scanning time and
increasing patient throughput.

17. Bismuth germinate (BGO)
• Absorption efficiency of BGO crystals is greater than
that of LSO crystals.
• The coincidence detection efficiency is approximately
80% for photon.
Cerium- doped gadolinium silicate (GSO)
• Can detect gamma rays over wide energy spectrum
from low-energy 28–35-keV photons from iodine-125
to 511- keV annihilation photons from FDG.

18. PET- CT Fusion
• PET is limited by poor anatomic detail, and
correlation with some other form of imaging,
such as CT/ MRI is desirable for differentiating
normal from abnormal radiotracer uptake.
• Precisely coregistered functional and anatomic
images can be obtained by performing a PET
study and a CT study on the same scanner
without moving the patient.

19. • As with CT imaging, MR imaging provides
accurate anatomic detail but also advanced
soft tissue contrast, allowing improved
discrimination of lesions and pathological
changes.
• Less radiation than PET/CT to the young pts
and those who has to undergo repeated
scans.

21. Scanning Technique
FDG myocardial metabolism imaging protocol:
• 4 hours fasting.
• Check blood glucose level with glucose strip.
• Ensure hyperinsulineamic euglycemic condition.
RBS <
100mg/dl
Give 90mg
glucose
Wait for 1 hr Give 2 U
Insulin
10mCi of FDG
i/v
RBS 100-150 5U Insulin 10mCi FDG
RBS 150-200 10U Insulin 10mCi FDG
RBS >200 Give 15U
Insulin
Check RBS after
30min
Put in sliding
scale
10mCi FDG

22. • Perform scan after 40 mins of injection of FDG.
• Inhibit speak for 20mins .
• No streneous exercise.
• Void urine and check whether diuretics used or
not.
• Process data and dipslay attenuation corrected
images in cardiac axis projections (short axis ,
vertical long axis and horizontal long axis).

23. 13 NH3 Non gated Rest- stress
Myocardial Perfusion imaging protocol
• 12 lead ECG and BP monitoring.
• Inject 30mCi 13 NH3 and scan after 5 mins.
• Give dipyridamole at 0.142mg/kg/min for 4
mins.
• Then again give 30mCi 13 NH3 and scan after 5
mins.
• Give aminophyline at 100mg iv slowly.
• Process data.

24. Terms used Myocardium Coronary
artery disease

25. i
Important prognostic
information can be obtained
by myocardial perfusion
imaging.
Normal findings at Stress-
rest myocardial perfusion
indicates that a person have
very low less than 1% event
rate future cardiac death or
non fatal MI , even when
Echocardiography and
angiographic findings are
positive.

26. Infarcted Myocardium

27. Hibernating Myocardium
• Retains cellular integrity despite reduced
perfusion but cannot sustain high energy
requirement of contraction.
• FDG pet is considered the standard of
reference for detecting hibernating
myocardium that may be amenable to
revascularization.

28. Hibernating Myocardium

29. SPECT vs PET

30. PET imaging of atherosclerotic disease
• Atherosclerosis is a leading cause of morbidity and
mortality.
• The disease is more than simply a flow-limiting
process and that the atheromatous plaque
represents a nidus for inflammation with a
consequent risk of plaque rupture and
atherothrombosis, leading to myocardial infarction or
stroke.
• Positron emission tomography (PET) has allowed the
metabolic processes within the plaque to be
detected and quantified directly.

31. • Frequently used invasive angiography remains the
gold standard anatomical imaging technique, non-
invasive modalities (CT angiography or perfusion) are
increasingly being used for individuals with stable
symptoms and low to moderate risk profiles.
• But these gives detail about the atherosclerotic
stenosis of the coronary vessels and fails to describe
about the stability of the plaque.

32. • Significant atheroma burden with a high risk
of subsequent cardiac events may be present
in the absence of luminal stenosis due to
outward artery remodeling.
• Positron emission tomography (PET) is one
such imaging modality that can detect and
quantify the pathophysiological processes
associated with atherogenesis and subsequent
plaque destabilization.

33. PET Radioligands
• Inflammation (with radioligands targeting
macrophages, including
18Ffluorodeoxyglucose, somatostatin receptor
ligands, and translocator protein ligands).
• Microcalcification :18F-sodium fluoride.
• Hypoxia :18F-fluoromisonidazole.

34. Pathophysiology
• Glucose transporter member (GLUT) 1 and 3, which
are upregulated during atherogenesis due to hypoxia
within the atheroma core.
• Silvera et al. imaged individuals with vascular risk
factors and found FDG TBR(Tissue to background
ratio) mean to be higher for lipid-rich plaques, which
are often vulnerable to rupture, than for collagen-
rich or calcified plaques with a lower risk of rupture.

35. Standarized Uptake Ratio
• The SUV is a semiquantitative assessment of the
radiotracer uptake from a static (single point in
time) PET image. The SUV of a given tissue is
calculated with the following formula:
tracer activity in tissue
injected radiotracer dose/patient weight
• The mean SUV is the mathematical mean of all
the pixels in the region of interest
• The minimum and maximum SUV are values of
the pixel with the lowest and highest SUV,
respectively.

36. • TBR was devised to correct for blood uptake of
radiotracer, the (blood pooling) effect.
• TBR is calculated as the ratio of the SUV of the
arterial wall to the SUV in the mid-lumen of a
large vein with no evident spill-over effect
from neighboring tissues.

37. Findings
• FDG uptake has been shown to identify symptomatic
carotid plaques that were non-stenotic on high-
resolution MRI, supporting the concept that the
severity of stenosis is not the sole determinant for
plaque rupture.
• Similarly, carotid SUVmean and TBRmean are
significantly higher for cohorts with acute coronary
syndrome than for those with chronic stable angina.

38. FDG-PET/CT showing
areas of focal radiotracer
uptake in the wall of the
descending aorta
(arrows)

39. • Dynamic contrast enhanced(DCE) MRI has
been shown to have superior spatial
resolution than PET/CT, and contrast
enhancement has been particularly effective
in the assessment of fibrous cap thickness and
lipid core volume, where the former enhances
while the latter fails to enhance.

40. 18F-Sodium Fluoride
• Inflammation is not the sole metabolic process
contributing to plaque vulnerability
• Inflammation within the atheroma can promote
microcalcification, the formation of deposits of calcium
smaller than 50 μm, through cytokine-mediated
promotion of osteoblast-like cells derived from vascular
smooth muscle cells.
• Both macrophage burden and osteogenic activity
increased with plaque progression.
• Microcalcification may predispose to plaque rupture
either through mechanical disruption to the fibrous cap
and/or provoking ongoing inflammation around the
deposits.

41. • 18F-sodium fluoride (NaF) used in PET imaging is able to
identify areas of microcalcification in vivo because the
radiolabeled fluoride is taken up at sites of mineralization,
where it replaces the hydroxyl group of hydroxylapatite.
• A prospective study has shown that NaF TBRmax is higher
in individuals with coronary artery disease, stable angina,
or previous cardiovascular events .
• Increased tracer uptake has been shown to be associated
with symptomatic coronary plaques, with the increased
uptake seen in morphologically high risk but unruptured
plaques suggesting that uptake reflects the
microcalcification process rather than increased surface
area following plaque rupture.

42. Lower limb 18F-NaF
imaging: non-contrast CT
(top left) with a rim of
calcification of the vessel,
18F-NaF PET (top right), and
fused 18F-NaF PET/ CT
(bottom left) of the
femoral artery (arrow) at the
level of the adductor canal,
demonstrating significant
vessel uptake in this
symptomatic patient. In
addition, there is prominent
uptake seen in the
vessel at the same level on
the coronal image (bottom
right)

43. Quantifying Hypoxia
• Atherosclerosis is often associated with hypoxia,
presumably due to an increasing oxygen demand
from foam cells.
• This likely results from reduced diffusion efficiency
from lumen to wall as plaque thickness increases.
• Whereas structural imaging techniques can assess
the size of the necrotic core of the plaque, PET
imaging using 18F-fluoromisonidazole (FMISO) can
measure the effects of hypoxia within the core
directly.

44. Cardiac Tumors
• Primary cardiac tumors are rare, with an
incidence ranging from 0.001% to 0.028% in
autopsy reports.
• Approximately 20%–25% of these tumors are
malignant, with angiosarcoma being the most
common malignant cardiac tumor.
• In contrast, secondary cardiac tumors, such as
metastasis to the heart from other malignant
tumors, occur more frequently.

45. • Preoperative differentiation of the benign and
the malignant tumors is necessary.
• Catheter-based biopsy is not suited in most of
the tumors.
• CT/ MRI may help in differentiation but
without sufficient accuracy.
• Molecular imaging methods such as 18F-FDG
with PET can visualize tumor metabolism and
thereby assess metabolic activity.

48. Cardiac Tumors

49. • FIGURE 3. A 59-y-old
woman presenting with
pleural, eripcardial
effusion and chest pain.
Cardiac CT revealed left
ventricular epicardial
tumor (A, arrow). MR
images show
hypervascular epicardial
tumor (C, T2
hyperintense; D, contrast-
enhanced T1) and large
pericardial effusion. 18F-
FDG PET/CT revealed low
uptake within tumor (B,
arrow)

50. Cardiac tumors
A 48-y-old man presenting
with incidentally diagnosed
cardiac mass in left atrium on
echocardiography: transaxial
slices zoomed to heart (left),
maximum-intensity projection
of trunk (middle), and
histology image (right).
SUVmax of cardiac tumor
(yellow arrows) was not
increased against background,
and there were no further
18F-FDG–positive lesions
throughout whole-body 18F-
FDG PET/CT. Histologic work-
up after tumor resection
revealed benign primary
cardiac myxoma.

51. Cardiac tumors
• A 48-y-old woman initially
presenting with dyspnea
and pleural effusion:
transaxial slices zoomed to
heart (left), maximum
intensity projection of trunk
(middle), and histology
image (right). Thorax CT
revealed right atrial tumor
mass, which on PET showed
strong 18F-FDG uptake
(green arrows). Whole-body
18FFDG PET/CT assessed
diffuse bone marrow
metastases (pink arrows,
right). Histologic work-up of
tumor biopsy revealed
malignant primary cardiac
tumor and angiosarcoma.

52. Cardiac Sarcoidosis
• MR imaging informs about myocardial structure, function,
and the pattern of injury whereas 18F-FDG–PET informs
about myocar
• MR+PET+ patients demonstrated increased 18F-FDG uptake
co-localizing with regions of LGE (Late Gadolinum E
Enhancement) images and were considered to have
imaging evidence of active cardiac sarcoidosis.
• MR+PET– patients had characteristic LGE appearances but
no increase in 18F-FDG activity, suggesting chronic scarring
secondary to “burnt-out” sarcoidosis, whereas MR–PET–
patients had no evidence of cardiac sarcoidosis
involvementdial and extra-cardiac inflammation.

53. Sarcoidosis
Magnetic resonance (MR) and
positron emission
tomography (PET) images
from 4 patients with active
cardiac sarcoidosis in whom
characteristic patterns of
myocardial late gadolinium
enhancement (left
column) co-localize with
increased 18F-
fluorodeoxyglucose uptake
(fused images, right column)

54. Myocarditis
• Patients with myocarditis commonly present with
troponin-positive chest pain but a normal
coronary angiogram.
• MR scanning is already widely used to confirm
the diagnosis and rule out myocardial infarction
based on the characteristic pattern of mid-wall
LGE.
• In certain cases, addition of 18F-FDG–PET
scanning might prove complementary, indicating
whether the underlying disease process is active.

55. Myocarditits
MR/PET imaging of a 25-year-old
woman with pericarditic chest
pain. (A) The late gadolinium
enhancement (LGE) images
demonstrate linear mid-wall LGE
consistent with
myocarditis. (B) Increased 18F-
fluorodeoxyglucose (18F-FDG)–
PET uptake co-localized with LGE
on fusion image indicating active
disease

56. Cardiac Amyloidosis
• MR scanning is a well-established tool in the
diagnosis of cardiac amyloidosis.
• However, MR scanning is unable to
differentiate between the 2 predominant
forms of amyloid: acquired monoclonal
immunoglobulin light-chain and transthyretin
related (TTR).
• Different prognoses and emerging treatments.

57. • Patients with TTR amyloid exhibited increased
myocardial activity of the PET bone tracer 18F-
fluoride than patients with acquired
monoclonal immunoglobulin light-chain
amyloid.
• Moreover, increased PET activity was
observed to co-localize with the pattern of
injury observed on LGE.

58. Limitations of PET- CT
Misregistration artifact:
• Patient motion in PET-CT imaging can produce significant
artifacts on the fused images and may cause confusion as
to the correct position of the origin of the detected photon.
• Patient motion is minimized by carefully instructing
patients not to move during the study.
• Placing them in a comfortable position before the start of
the study
• Ensuring that they are not taking diuretics, which may
otherwise require them to evacuate the bladder during the
study
• Having patients empty their bladder before the start of the
study

59. • Respiratory, cardiac and the bowel motions
are unavoidable.
• Patient motion may appear as a mismatch
between two sets of images.
• By comparing the activity of the tracer over
normal organs and their CT images artifacts
can be determined and can be accounted for
interpretations of the images.

60. Misregistration artifact. FDG
PET–CT was performed for staging
in a patient with carcinoma of the
left breast. Axial fused FDG PET–CT
image shows a lymph node in the
left axilla (straight arrow). Focal
ypermetabolism in the node
(curved arrow) appears lateral to its
expected location in the axilla and
overlies axillary fat instead
of the node. Misregistration
between the CT and PET images is
due to patient motion between the
CT and PET portions of the
examination.

61. Attenuation correction artefacts.
Attenuation correction artifact.
(a) Attenuation-corrected
coronal fused FDG PET–CT
imageshows a focus of intense
hypermetabolism in the right
supraclavicular region (arrow).
(b) Attenuation-uncorrected
fused FDG PET–CT image
obtained at the same level
shows that the apparent focus
of hypermetabolism is an
attenuation correction artifact
from a pacemaker (arrow)

62. Attenuation (transmission) correction
artifacts
• Attenuation (transmission) correction artifacts
can occur where there are highly attenuating
objects in the path of the CT beam, such as
hip prostheses, pacemakers, dental devices,
and contrast- enhanced vessels.
• PET-CT attenuation corrects (overcorrects
photopenic areas adjacent to high attenaution
structures at CT and makes them
hypermetabolic.

63. Patient with transthyretin-
related amyloidosis
(ATTR). (A) Short-axis fused
MR/PET image
demonstrating increased
myocardial 18F-sodium
fluoride uptake co-localizing
to areas of LGE (white
arrows) in the inferolateral
wall.

64. • If the patient has undergone strenuous
activity preceding or following injection of
FDG, normal muscles may take up the
radiotracer and show increased activity on the
PET images.This is usually easy to distinguish
from malignancy by comparison with the CT
images for a focal mass or lesions.
• FDG uptake in normal muscle is diffuse and
frequently symmetric.

65. Normal physiological uptake
• brain tissue
• skeletal muscle, especially after strenuous activity
and laryngeal muscles following speech
• myocardium
• gastrointestinal tract, e.g. intestinal wall
• genitourinary tract: FDG is excreted via the renal
system and passes into the collecting systems
• brown fat
• thymus
• bone marrow

66. False-positive FDG uptake
This may occur due to the following conditions:
• granulomatous disease
• abscess
• surgical changes
• foreign body reaction
• excessive bowel uptake with metformin therapy
• inflammation (although at times e.g. evaluating
for vasculitis, this may be the finding of interest)

67. THANK YOU

68. Refrences
• An Introduction to PET-CT Imaging; Vibhu Kapoor et al;
RadioGraphics 2004; 24:523–543.
• PET Imaging of Atherosclerotic Disease: Advancing Plaque
Assessment from Anatomy to Pathophysiology Nicholas R. Evans et
al. April 2016.
• Cardiac PET/CT for the Evaluation of Known or Suspected Coronary
Artery Dise Marcelo F. Di Carli ase et al; RadioGraphics 2011;
31:1239–1254.
• Differentiation of Malignant and Benign Cardiac Tumors Using 18F-
FDG PET/CT;Kambiz Rahbar et al:J Nucl Med 2012; 53:1–8.
• SPECT and PET CT in coronary artery disease,Hossein Jodvar;
Radiographics 1999.