Principles and application of PET CT & PET MRPresentation Transcript
PRINCIPLES &PRINCIPLES &
APPLICATIONS OF PET - CTAPPLICATIONS OF PET - CT
and PET - MRand PET - MR
Moderator: Prof. (HOD) R .K. GOGOI
Cancer is one of leading causes of morbidity and mortality in
Most radiologic procedures map the anatomy and morphology of
tumors with little or no information about their metabolism
Positron emission tomography (PET) is a coalition of physics,
chemistry, physiology, and medicine united in an effort to measure
physiologic parameters noninvasively.
Positron Emission Tomography and Computed Tomography / MRI
is the combination of functional imaging as well as anatomical
1978 the first commercial
PET scanner was
70s and 80s PET was
mainly used for research
1990s being used in
First approval in 1998.
PRINCIPLE OF PETPRINCIPLE OF PET
The concept of PET is to radiolabel a bio-compound, inject it into the patient,
and then measure its bio-distribution as a function of time to determine
physiologic quantities associated with the biocompound.
All PET compounds are radiolabeled with positron-emitting radionuclides.
These radionuclides have decay characteristics that enable localization in the
A positron is emitted from the nucleus, travels a short distance, and annihilates
with its antiparticle (an electron), which results in two 5 I l-keV photons
traveling in opposite directions.
After both photons are detected, the activity is localized somewhere along the
line defined by the two detectors.
511 keV photon
511 keV photon
E = mc2
Synthesizing radiopharmaceuticals from the tracers
administering the radiopharmaceutical to a patient
measuring the resulting radioactivity distribution in an
organ of interest
interpreting activity distribution as a function of
A PET study consists of
PRODUCTION OF RADIONUCLIDEPRODUCTION OF RADIONUCLIDE
PET radionuclides are positron emitters.
There are 5 convenient nuclides-
HALF LIFE (min)
Rubidium- 82 1.23
Fluorine – 18 109
Oxygen- 15 2
Nitrogen- 13 10
Carbon- 11 20
Commonly produced isotopes : “F O N C”
SYNTHESIS OF F-18 &FDGSYNTHESIS OF F-18 &FDG
Over 500 PET compounds have been
synthesized since 1970.
Natural substrates such as amino acids,
analogues ,fluorinated glucose &drugs.
MC used is a glucose analogue, 2-[F18]fluoro-
Why is 18 F the most used positron emitter?
18F is a small atom.
its addition to a molecule does not deform it to the point
where it is not recognized by the body anymor
has a half-life of 109 minutes.
This is long enough to perform a complicated chemistry
(labelling) , and to allow transport over some distance.
It is also long enough to keep the radiation burden to patient
[18F]-labeled 2-deoxyglucose (FDG) is used in neurology,
cardiology and oncology to study glucose metabolism. FDG is
potentially useful in differentiating benign from malignant forms of
lesions because of the high metabolic activity of many types of
[15O]-labeled water is used to evaluate myocardial oxygen
consumption and oxygen extraction fraction. It can also be used to
measure tumor necrosis.
[13N]-labeled ammonia can be used to measure blood flow.
[11C]-labeled methionine and leucine can be used to evaluate
amino acid uptake and protein synthesis, providing an
indicator of tumor viability.
Radiolabeled fluorine ion [18F-] was once a standard agent for
clinical bone scanning.
A typical production schedule for FDG is 3hours in duration,
starting from the time the chemist walks into the laboratory
until the radiochemical is produced.
The synthesis is 50%-60% efficient, so accounting for this and
the radioactive decay, about 200 mCi (7.4 GBq) of FDG is
available at the end of the synthesis.
A patient usually receivesA patient usually receives 10 mCi (370 MBq).
If two scanners are available so that a patient can receive an injectionIf two scanners are available so that a patient can receive an injection
every half hour,every half hour, one production run will allow scanning aboutrun will allow scanning about six
patients per day..
Principle of metabolic imaging with FDG
Glucose 18 FDG Blood vessel
Glucose 6 Phosphate 18FDG 6 Phosphate
Fructose 6 Phosphate
Anaerobic resp Citric acid cycle
SCANNER DESIGNSCANNER DESIGN
A positron emission
tomography (PET) scanner
is a large machine with a
round, doughnut shaped
hole in the middle
Within this machine are
multiple rings of detectors
that record the emission of
energy from the radiotracer
in your body.
A nearby computer aids in
creating the images from
the data obtained by the
camera or scanner.
SCANNER DESIGN….SCANNER DESIGN….
Detectors are 18-40 rings of crystals forming a
cylindrical field of view about 15cm long that can
acquire many slices of coincidence data
PET scanners use crystals with higher density &
higher Z numbers due to sensitivity
Group of crystals is put together into a block
Four PMT’s to each block of crystal
Use “electronic collimation” to detect location of
SCANNER DESIGN….SCANNER DESIGN….
Localizing the site of impact is achieved by
measuring the light detected in each PMT
Signal is then amplified
System must be able to determine which signals
come from paired 511keV photons and record the
time of detection (timing discriminator)
Coincidence circuit then examines signals to
confirm it if it occurred with in the time window
CRYSTALS USED IN PETCRYSTALS USED IN PET
BGOBGO – Bismuth Germinate
LSOLSO – Lutetium
GSOGSO – Gadolineum
YLSOYLSO – Yttrium Lutetium
COINCIDENCE DETECTIONCOINCIDENCE DETECTION
Photons should arrive with in a certain time of
A coincidence timing window allows detection
of the PMT electrical signal from photon pair
If it falls within timing window it is registered
as a true event
When two different annihilation events are
detected with in the timing window is known as
DATA ACQUSITIONDATA ACQUSITION
The detection of photon pairs by opposing
crystals create one event (LOR)
Millions of these event will be stored with in
sinograms and used to reconstruct the image
Spatial resolution is determined by the size of
crystal and their separation and is typically 3-
PET is 50-100 times more sensitive and
produces higher quality than a SPECT
Reconstruction is similar to SPECT
PET reconstruction can be performed with
a variety of algorithms
o Filtered back projection
o Iterative reconstruction(ordered subset
ATTENUATION CORRECTIONATTENUATION CORRECTION
Mathematical attenuation correction techniques may
be used if tissue attenuation is the same at all areas
within a transaxial slice .
Measured attenuation may be performed by two
– Transmission scan using a radioactive source rotating it
around the patient
– CT scan to measure tissue density
The ability to correct for attenuation improves quality
and permits absolute quantification of radioactivity in
Resolution in PET is determined by three factors:
distance the positron travels before it annihilates with an electron,
variation in angle between the two annihilation photons, and
physical size of the detectors.
A positron will travel between 0.5 and 2 mm in tissue before
annihilation, depending on its energy.
Typical detector sizes are 1 -3 mm.
The best possible resolution of a PET scanner is 1-2mm.
Typical clinical scanners have a resolution of approximately
PET vs. CT & MRIPET vs. CT & MRI
PET CT and MRI
Shows extent of disease
Detects changes in body
Can help in monitoring
treatment and shows it’s
Simply confirms the presence
of a mass
Reveals disease earlier, can
Can detect whether a mass is
benign of malignant
Can detect abnomalities before
there is an anatomical change
SAFETY ASPECTS OF PETSAFETY ASPECTS OF PET
PET has 511Kev gamma rays energy, that is 3 times of
140Kev gamma ray energy of Technitium99m
Due to their high energy 16 times more lead is required to
obtain the same stopping effect for 511Kev photons as
compared to 140Kev photons
SAFETY ASPECTS OF PETSAFETY ASPECTS OF PET
So Tungsten shielding
is used for Positron
It provides 1.4 times
the shielding capability
for the same thickness
CONTRA INDICATIONSCONTRA INDICATIONS
Use of caffeine, tobacco, or alcohol in
past 24hours before scan
Using medicines that change metabolism
PRINCIPLE OF PET-CTPRINCIPLE OF PET-CT
PET-CT FUSIONPET-CT FUSION
FDG PET is a strictly functional modality and lacks anatomic landmarks.
Unless anatomic correlation is available to delineate normal structures,
pathologic sites of FDG accumulation can easily be confused with normal
physiologic uptake, leading to false-positive or false-negative findings.
Coregistration of PET scans with CT using a combined PET-CT scanner
improves the overall sensitivity and specificity of information provided by
PET or CT alone .
advantage is ability to correlate findings at two complementary imaging
modalities in a comprehensive examination. Hence, PET-CT provides more
precise anatomic definition for both the physiologic and pathologic
uptake seen at FDG PET
Max coverage during combined study
Distance betwn pet and ct scanner
SCANNING TECHNIQUESCANNING TECHNIQUE
Nil orally for approximately 4–6 hours
avoid caffeinated or alcoholic beverages but can have water
during this period.
blood glucose level of less than 150 mg/dL is desirable.
Avoid strenuous activity to avoid physiologic muscle uptake of
water-soluble iodinated contrast media orally for bowel
opacification except for head and neck study.
10 mCi injected intravenously
Patient activity and speech are limited for 20 minutes
immediately following injection
Pet study is started 60 mins after injection.
Contrast material–enhanced helical CT is performed following injection of
125 mL of a contrast medium at a rate of 4 mL/sec by using a power
Whole-body PET-CT study scanning begins at the level of the skull base
and extends caudally to the level of the symphysis pubis.
The PET scanner is located behind the CT scanner and housed in the same
extended-length gantry. PET is performed following the CT study without
moving the patient in the caudocranial direction,starting at the thighs to
limit artifacts from the FDG metaboliteexcretion into the urinary system
Typical scout image obtained during an FDG PET-CT study. The blue-purple rectangle
represents CT coverage during the study, and each overlapping green rectangle
represents PET coverage.
INTERPRETATION OF IMAGESINTERPRETATION OF IMAGES
PET provides images of quantitative uptake of the
radionuclide injected that can give the concentration of
radiotracer activity in kilobecquerels per milliliter .
Methods for assessment of radiotracer uptake –
• visual inspection
• standardized uptake value (SUV)
• glucose metabolic rate
LIMITATIONS AND ARTIFACTS OF PET-CTLIMITATIONS AND ARTIFACTS OF PET-CT
1.Patient motion 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
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
or catheterizing the bladder.
2.Attenuation (transmission) correction artifacts highly attenuating
objects in the path of the CT beam, such as hip prostheses,
pacemakers, dental devices, and contrast-enhanced vessels
ADVANTAGES OF PET-CTADVANTAGES OF PET-CT
1. helpful in accurate localization of small areas of increased radiotracer
activity that would have been difficult or not possible to localize on
PET images alone .
2. helps in distinguishing structures that normally show high metabolic
activity from those with abnormally increased activity.
3. PET-CT combines the advantages of the excellent functional
information provided by PET and the superb spatial and contrast
resolution of CT
4. Finally, attenuation correction for quantitative or semi quantitative
assessment of data is possible by using the CT data,
Whole-body PET/MRIWhole-body PET/MRI::
The Future in OncologicalThe Future in Oncological
PET/MRIPET/MRI: TECHNICAL EVOLUTION: TECHNICAL EVOLUTION
The idea to combine PET and MRI arose as early as the mid
1990s, even before PET/CT was introduced.
The PET/MRI combination requires 3 risky technologic steps
that modify state-of-the-art PET and MRI.
1. First, the photomultiplier technology must be replaced with magnetic
field–insensitive photodiodes .
2. Second, compact PET detectors must be constructed so that it shouldn't
interfere with the field gradients or MR radiofrequency.
3. Finally, the MRI scanner must be adapted to accommodate the PET
detectors and to allow simultaneous data acquisition without mutual
Based on the technologic challenges to combine PET and MRI into a
single gantry, Philips and Siemens proposed 2 fundamentally different
prototype PET/MRI designs.
In the Siemens prototypes include 4 dedicated brain PET scanners
that fit into a standard 3-T clinical MRI scanner.
The PET/MRI system, together with a dedicated radiofrequency head
coil, allows simultaneous PET/MRI data acquisition of the human
brain or body extremities.
Philips developed a PET/MRI design in which the gantries are
approximately 2.5 m apart but share a common patient handling
system. This implementation does not allow for simultaneous data
acquisition and, therefore, results in longer examination times.
Scanner DesignScanner Design
CLINICAL POTENTIAL OF PET/MRICLINICAL POTENTIAL OF PET/MRI
It is reasonable to expect that brain PET/MRI will provide new
insights in the field of neuroscience and neurologic disorders, such as
neuro degeneration, brain ischemia, neuro oncologyor seizures .
It is feasible with current prototypes and future-generation systems to
simultaneously study brain function, metabolism, oxygen
consumption, and perfusion.
In oncology, an accurate spatial match between PET and MRI data is
mandatory for both radiation therapy planning and biopsy guidance.
Combining PET with cardiac MRI may enable detection and
differentiation of vulnerable plaques and diseased myocardium.
Advantage of PET/MRI over PET/CT
1. is not associated with significant radiation exposure
2. has a much higher soft tissue contrast.
3. MRI allows for additional techniques - such as angiography, functional MRI
,diffusion ,spectroscopy and perfusion techniques within one single
PHYSIOLOGIC VERSES PATHOLOGIC FDG UPTAKEPHYSIOLOGIC VERSES PATHOLOGIC FDG UPTAKE
of FDGof FDG
There are several sites of normal physiologic accumulation ofFDG. FDG
accumulation is most intense in the cerebralcortex, basal ganglia,
thalamus, and cerebellum. The myocardiumexpresses insulin-sensitive
glucose transporters, which facilitatethe transport of glucose into muscle. A
recent meal often causes intense myocardial FDGuptake because of the
associated elevated serum insulin levels
Because FDG appears in the glomerular filtrate and, unlike glucose,is not
reabsorbed in the tubules, intense FDG activity is seenin the intrarenal
collecting systems, ureters, and bladder
The most common areas of normal distribution of FDG
include the brain, myocardium, and genitourinary tract.
SEMI QUANTITATIVE VALUE- CALCULATION OF INTENSITY
OF FDG UPTAKE IN REGION OF INTERST.
SUV-5 Indicates five times the average uptake.
RISUV - new index, Retention Index SUV after 3 hours.
STANDARDISED UPTAKE VALUE
Physiologic FDG uptake
The distribution of FDG
within a normal individual (MIP).
•Moderate to high FDG uptake is noted in patients with thymic
rebound andshould not be confused with asymmetric uptake due
to lymphoma in this location .
•In pediatric patients, anatomic correlation is necessary following
chemotherapy to differentiate the enlarged thymus from residual or
recurrent disease at this location, especially with focal thymic
Physiologic thymic uptake in a 23-year-old woman with a
history of Hodgkin disease of the chest who was referred for
Low to moderate FDG uptake is noted in the distal esophagus,
particularly in patients with gastroesophageal reflux secondary
to inflammatory changes.
However, high-grade uptake in the same location maybe
caused by malignant processes (ie, carcinoma of the distal
esophagus, usually associated with morphologic esophageal
Nonneoplastic esophageal uptake in a 21-year-old woman with a
history of non-Hodgkin lymphoma
Esophageal adenocarcinoma in a 52-year-old man who was
referred for presurgical evaluation.
THE ROLE OF PET/CT IN LUNG CANCER
Assessment of the solitary pulmonary nodule (SPN)
Staging of non-small cell lung cancer (NSCLC)
Assessment of mediastinal lymphadenopathy
Identification of distant metastatic disease
Detection of recurrent disease
Solitary pulmonary noduleSolitary pulmonary nodule
? Benign or malignant
No activity. Diagnosis: benign bronchocoele
nodules are malignant.
If an FDG positive
nodule is found, it
should be assumed to
be malignant until
Without the aid of
PET/CT it can be
difficult to distinguish
active tumor from
collapsed lung or
Identification of distant metastatic disease
Evidence suggests that the
removal of a solitary adrenal
deposit at the time of resection
of the lung primary results in
an increased life expectancy.
Liver, adrenal, brain and bony
deposits are common with
lung cancer but many of the
lesions are undetected in
the course of conventional
PET/CT IN RADIOTHERAPY PLANNING
Patient for radiotherapy. Where does the tumor end and the
collapsed lung begin ?
The Role of PET/CT in Lymphoma
Assess response to therapy/residual disease
Identify recurrent disease
Initial diagnosis and staging
Identify suitable sites for biopsy
An example of stage 4
disease. NHL with
disease in the
neck, and abdomen
ASSESSMENT OF TREATMENT
Pretherapy and post
studies showing a
response to therapy.
Brown fat activation can cause
confusion and care must
be taken to ensure that each area of uptake
corresponds to fat. Activated brown fat is
seen more commonly in thin individuals
during the winter months, but there is also
an increased incidence in women and in
patients suffering from lymphoma
Head and Neck
Moderate to high FDG uptakeis noticeable in the muscles,
including the ocular muscles.
may be a potential source of false-positive findings inpatients
with malignant head and neck tumors.
Contraction-induced FDG uptakein cervical muscles in tense
patients can be confused with lymphnode metastasis which
constitutes a serious problem in patients with
asymmetric muscleuptake due to prior neck dissection.
FDG accumulates in the striated laryngeal muscles in
proportion to contractile activity during speech.
This phenomenon is a major concern and may lead to false
readings in patients with head and neck cancers .
Rigorous approach to preventing physiologic FDG uptake in
thelaryngeal muscles should be adopted to avoid false-positive
Physiologic laryngeal uptake in a 52-year-old woman
with squamous cell carcinoma of the floor of the mouth.
Primary tumor of the larynx in a 45-year-old man with epiglottic
carcinoma who was referred for presurgical evaluation.
NEUROLOGY INDICATIONSNEUROLOGY INDICATIONS
Tumor recurrence versus radiation necrosis
Monitoring response to therapy
SEIZURE FOCUS IDENTIFICATION
Brain injury- vascular, trauma
Psychiatry- depression, schizophrenia,anxiety
Movement disorders with 18F-dopa
Miscellaneous- infection, substance abuse,eating disorders
rt parietal gbm
LOSS OF VISION BOWEL & BLADDER INCONTINENCE
SINCE I MONTH
High precision Radiation therapy Planning
in the lesion
Comparison of MRI time-to-peak (TTP) and PET O2
extraction fraction (OEF) images
Extensive hypo metabolism of entire brain
parenchyma, except thalami & basal ganglia
PET in NeurologyPET in Neurology
The Active Human BrainThe Active Human Brain
PET in Brain DisordersPET in Brain Disorders
Simultaneous PET/MRI study in
Hypo metabolism in left temporal lobe secondary to epilepsy
Abdomen and Pelvis
Moderate to highFDG uptake is visible in the muscles that contribute to
breathingin patients with chronic obstructive pulmonary disease.
due todifficulty in breathing and use of accessory muscles to facilitate
In addition, due to an imbalance between oxygen supplyand increased demand,
the decrease in oxygen delivery causesa switch to anaerobic metabolism.
Hence, the increaseduptake seen in the diaphragmatic cruces may be the result
of accentuated abdominal breathing effort and the anaerobic metabolismthat
leads to increased FDG uptake similar to the physiologicalterations in cancer
Any disease process involving theceliac or perigastric lymph nodes (eg,
lymphoma, nodal metastaticdisease) can be difficult to interpret in patients with
diaphragmaticuptake, especially in the posttherapy setting.
Physiologic diaphragmatic uptake in a 49-year-old woman with a
history of abdominal lymphoma and severe COPD who was
referred for posttherapy follow-up.
Low to moderate uptake is usually observed in
Focal and irregular uptake in the stomachis
usually due to a malignant process;
nevertheless, local gastritiscannot be excluded
with certainty without the help of CT.
Physiologic gastric uptake in a 52-year-old man with colorectal
cancer who had undergone surgical tumor resection.
Gastric cancer in a 59-year-old woman
The importance of FDG PET in the evaluation of colorectal
canceris well established.
Both small and large bowel may demonstratevarying degrees
of FDG uptake, usually with a diffuse and linearpattern.
However, focal physiologic uptake is not an uncommon
finding in short segments of the bowel.
UnlessCT correlation is available, the configuration of uptake
in thesecases may be indistinguishable from malignant
Adenocarcinoma of the cecum in a 77-year-old man.
Gallbladder uptake of FDG is not a common finding.
When activity is observed in this anatomic location,
choleductalcancer, adenocarcinoma of the gallbladder,
and primary or metastaticdisease of the liver should be
considered in the differentialdiagnosis.
CT correlation is most helpful in delineatinganatomic
landmarks and distinguishing a benign gallbladder
variantfrom malignant lesions.
Chronic cholecystitis in a patient with papillary thyroid
cancer who underwent thyroidectomy
Liver metastasis in a 55-year-old man with rectal adenocarcinoma.
Unlike glucose, FDG is not reabsorbed by the renal tubules
Thus, significant FDG accumulation is seen in theintrarenal
collecting system and renal pelvis.
This accumulationmay interfere with the identification of
renal parenchymal orpelvic urothelial tumors.
However, anatomicinformation provided by CT allows proper
assessment and characterizationof renal masses
Renal cell carcinoma in a 60-year-old woman
Focal FDG accumulation in the ureters is a
common finding dueto the pooling of radiotracer
in the recumbent patient.
althoughthe intensity and location of uptake
usually allow accurateidentification of the ureters
in patients with abdominal malignancies, this
finding can be misdiagnosed as pelvic lymph
node metastasisor nodal lymphoma.
Physiologic uptake in the renal pelvis in a 66-year-old man
with a history of colorectal cancer .
There is usually no FDG accumulation in the uterus, althoughfocal
FDG uptake in the uterus during menstruation has beendescribed.
can beattributed to heavy bleeding or to necrotic endometrial
epitheliumdue to sudden reduction of estrogen and progesterone
levelsat the end of the secretory phase of the menstrual cycle.
Itmay not be possible to differentiate this uptake pattern fromuterine
carcinoma, even with the help of PET-CT .
However, FDG uptake is usually more irregular, diffuse, and
extensive in uterine cancer .
Physiologic uterine uptake in a 40-year-old woman with a
history of lymphoma who was referred for posttherapy
Endometrial cancer in a 66-year-old woman.
Cardiac PET andCardiac PET and Myocardial perfusion ImagingMyocardial perfusion Imaging
Rb Distributed in the myocardium depending on the regional blood flow
Rb delivery limited to ischemic or underperfused areas
These areas will appear as defect on initial images
On delayed images(2-4hrs) post inj
Defects resolves due to redistribution which reflects not only eventual
accumulation of Rb in viable ischemic zones but release & washout from
normally perfused area
(Areas of myocardial infarction or fibrosis present as permanent defects
due to lack of perfusion)
CARDIAC PET and PET CT IMAGING
The stress images
show a severe
that is completely
reversible at rest
The first heart has a mycardial infarction. The
arrows point to damaged areas (‘dead’
tissue).Therefore it is assumed that the patient
will not benefit from heart surgery.
The second heart is normal
Example: Myocardial Viability
PET IN INFLAMMATORY CONDITIONS
Hepatic and splenic uptake of FDG are generally low grade and
In the setting of infection, splenic uptake can be intense.
Acquired Immuno-deficiency Syndrome.
Till now, gallium imaging radionuclide imaging - study of choice in evaluating
opportunistic infections in AIDS patients.
FDG – PET – helpful in many CNS conditions in AIDS patients.
Lymphoma and toxoplasmosis are frequent CNS complications – not always
distinguishable at CT and MRI.
CNS LYMPHOMA- Highly metabolically active.
TOXOPLASMOSIS- metabolically inactive.
FDG PET of Infection and Inflammation1
Toxoplasmosis in an AIDS patient
Acquired Immuno-deficiency Syndrome
CNS lymphoma in a different AIDS patientCNS lymphoma in a different AIDS patient
2. Fever of unknown origin.
FDG PET- LT PL EFF: HYPERMETABOLIC FOCUS SUB PLEURAL
CTPA- LEFT LOWER LOBE PULMONARY EMBOLI,
WEDGE SHAPED PULMONARY INFARCT.
FINAL DIAGNOSIS- PULMONARY EMBOLISM C INFARCTION.
Increased metabolic activity in inflammation
results in increased FDG uptake.
Also occur in
a. inflammatory arthritis
b. acute fractures,
c. normally healing bone after surgery.
Differentiation between inflammatory and
Traditionally, a single time point SUV of 2.0–3.0 hasbeen proposed as the
optimal threshold for separating malignantfrom benign lesions.
With the exception of granulomatous lesions- malignant lesions shows
increased SUV values on delayed images i.e., increased RI SUV
( RETENTION INDEX SUV ).
DUAL TIME FDG PET imaging at two intervals appears promising now.
Lesions with decreased SUV s over time are likely to have a benign
etiology. Malignant lesions tend to have increase in SUV over time.
PET vs. SPECTPET vs. SPECT
PET have superior sensitivity and resolution
Greater flexibility of incorporating positron
labels into biomolecules
PET is more expensive and requires the
presence of an onsite cyclotron
Positron Emission Mammography
PEM is a specialized & improved
form of PET for imaging breasts
and other small body parts.
Camera and detectors are closer to
the area affected with cancer which
produces a very sharp detailed
image of tumors and cancerous
Can see cancers as small as 1.5 –
2mm about the width of a grain of
Also allows for the earlier
detection of elusive cancers such
as DCIS (ductal carcinoma in situ).
Breast PET MRIBreast PET MRI
Schematic diag of pet insert and mri coil
Understand the differences between whole-body PET and PEM
better spatial resolution (1-2 mm vs. 5-10 mm). This comes at the
cost of field-of-view
•Closer proximity of PEM detectors increases geometric
Allows lower dose/faster imaging/longer uptake time
differences between mammography and PEM
Transmission vs. Emission Imaging
Anatomical vs. Functional Imaging
Planar vs. Tomosynthesis (or Tomographic)
•Planar is single projection view with considerable tissue
•Tomosynth./tomographic is 3-dimensional volumetric image
Utilities, cost, dose
Detection of coincidence photons emitted during positron annihilationis the key to
PET imaging, whereas accurate coregistration ofthis quantitative/functional
information with the CT data isthe key to successful PET-CT imaging.
Specific attention topatient preparation, data acquisition, data reconstruction,and
image interpretation is crucial to obtaining high-qualityPET-CT images.
Fusion of the anatomic and functional imagesby using a dedicated PET-CT /Pet
mri scanner is exploited for optimalresults required in the management of complex
clinical scenariosfaced by our clinical colleagues. Having witnessed an impressive
technologic development of PET detector technology, first PET/MRI prototype
systems, and MRI-based PET attenuation correction, as well as encouraging clinical
and specifically preclinical PET/MRI results, we now seek opportunities to translate
these technologic advances into clinical benefits