Nuclear Medicine Flashcards
PET scanning mechanism
tracer accumulates in tissues of interest
radioactive tracer emits positrons during decay
positron travel short distance before annihilating with electron in the surrounding tissue
this creates energy in the form of 2 back to back / DIAMETRICALLY OPPOSITE 511 kiloeletronvolt gamma photons emitted in opposite directions
circle of gamma detectors measure pairs of gamma photons -i.e. arriving in the same small period nanoseconds of time - said to be in coincidence
locating exact position of collision
the positron assumed to met electron somewhere along the line of response
millions of lines of response recorded to map out 3 d distribution of positron emitting radionucleotide in the body
reconstruction gives pixel values proportion to radioactivity concetration in area of bodu
definition nuclide istope radioisotope radionuclide radiopharmaceutical
nuclide
atom with arrangement of protons, neutrons and electrons
isotope
nuclide with same number of protons, atomic number - neurtrons and protons and chemical properties
radioisotope
unstable isotope, emits radiation as nuclei undergo rearrangament more stable form
radionuclide
radioactive atom
nomenclature element plus atomic mass number
radiopharmaceutical = combination radionuclite with compound with physiological properties
what does gamma camera detect
distribution of radioactive substances in vivo
half life of technetium 99m
what is m
what is radiation emitted
6 hours
m is for metastable
emits gamma ray
why is Tc99m suitable
non toxic no immune response no pharm ation in isolation can mix with range of compounds eg Tc99m colloid for sentinel LN biopsy Tc99m MDP bone scan
what is used for glomerular filtration
chromium Cr 51 edetate (Cr 51-ethylenediamine tetraacetic acid; Cr 51-EDTA)
Tc-99m DTPA (diethylene-triamine-pentaacetate
how to do radiopharm scan
adequate hydration
bladder empty
sitting/prone gamma camera to back
inject radiopharmaceutical and acquire images 20-40 minutes
empty bladder to reduce dose to pelvic organs
3 phases of renogram
vascular phase
first few seconds,
phase should be removed from generated renogram
uptake phase from 1 min onwards
rate rises porportional to kidney function
2-5 min peak, rapid rise
transit phase
renal handling tracer gradual slope
elimination phase
any time after 3 min
after reaches peak
balance between uptake and elimination
rising curve uptake exceeds elimination
horizontal curve uptake and elimination balanced
1st Phase
Rapid uptake by tubular cells
(isotope reaches kidney within approx 15 seconds)
Reflects speed of injection and renal blood flow
2nd Phase – Renal handling
The transfer of tracer across tubular cells into lumen of nephron
3rd Phase – Excretory phase
Reflects efficiency of excretion
DTPA
where excreted
inert
90% excreted by glomeruli
no secretion or filtration
MAG 3 excretion
95% tubular secretion
can measure effective renal plasma flow as surrogate of GFR
MAG-3 principally excreted by tubular secretion 90%; 10% filtered
MAG3 is cleared by a combination of glomerular fi ltration and tubular
secretion, so it has greater kidney uptake, leaving less in the blood background. It is
therefore the preferred radiopharmaceutical
DMSA
better for function as has cortical parenchymal activity
anterior and posterior views
dose of furosemide
when to give
0.5 mg/kg up to 40mg
can give at T+20 if not emptied by 20 minutes
data acquisition for another 15 mins
if equivocal response then maximal diuretic response can be F-15
if venous access difficult eg in children, furosemide give immediately before radioactive tracer through same cannula F+0
types of renogram curve
type 1 normal
type 2 obstructed
type 3 a hypotonic - normal drainage from hypotonic renal pelvis, rises initially but rapid fall with diuretic
type 3b equivocal = rises initially but neither falls rapidly nor continues to rise following injection of furosmide
type 4 Homsy sign
transient response to diuretic, represents obstruction, VUR can look similar, represents intermittent hydronephrosis, giving -15 diuretic eliminates homsy sign
bone scan compound
methylene diphosphonate
what is energy of gamma rays emitted from pet
two of 511kEV gamma rays emitted in opposite directions
fdg
18F flurodeoxyglucose
This is an analogue of glucose, which is trapped
within cells following phosphorylation by hexokinase
half life of 18F
110 minutes
half life of 18F
110 minutes
half life 11C
20 minutes
11C pet vs 18F FDG pet for prostate ancer
FDG - low metabolic rate of prostate cancer
C11 better as map to lipid metabolism/cell membrane integrity
what is SUV
pixel values from pet scan expressed as units of kBq/kl normalised to injected activity and patient body weight to produced standardised uptake values SUV
how is renogram performed
patient well hydrated
drink 300-500mls water prior
empty bladder imm before test
positioned seated with back to camera to aid normal gravitational drainiage or supine with camera underneath couch
injection of radiopharmaceutical
immediately gamma camera starts acquiring dynamic series of images
one frame every 20s for 30-40 minutes
if kidney not drained by 40 min, and patient lying down, patient asked to stand up and final static image acquired
then patient empties bladder and post mic image acquired
drawing regions of interest
around kidney and other area for background activity
use of background curves
used to subtract background contribution from each kidney curve, resulting curve is the renogram
how is relative function calculated from mag 3
from first 1-3 minutes of renogram, rutland plot most accurate
Homsy’s sign
If the renogram curve initially starts to fall after
furosemide but then begins to rise again after a few minutes, this is known as
Homsy’s sign (Fig. 22.1d ). It is indicative of intermittent obstruction which only
occurs at high urine fl ow rates. In these cases, an F-15 renogram will probably
appear obstructed.
F-15 renogram curve when will have max diuresis
will have max diuresis by time renogram started
if curve rises mean ob at high flow
however no indication how kidney handles normal urine flows
how DMSA scan is done name where bind emitting radiation where accumulates how long wait which images taken
dimercaptosuccinic acid gamma emitting binds to PCT accumulates slowly renal cortex only small amount excreted patient waits for 2-4 hours to sufficient cortical uptake
supine on imaging couch
static views from kidney posterior anterior left posterior oblique and right posterior oblique
each view takes about 5 mins to get 200,000 to 500,000 counts
gamma camera in dmsa scan
using
how long per image
how calculate geometric mean
Gamma camera: detects gamma rays and their position, via collimator and photomultiplier
LEHR collimator, approx 5 mins per image (200,000-500,000 counts)
Static views from posterior, anterior, LPO and RPO
Region of interest around each kidney, exclude non-renal background
Relative function calculated from posterior and anterior view (geometric mean)
what is megabecquerel
1MBq = million atoms disintegrating/sec
1Gray
absorption of 1J of energy/kg (=100rads
Effective radiation dose (Sv)
Gy x type of radiation x tissue type/volume/time
MAG 3
how many mBq
mSV
secretion and filtration
Mercaptoacetyltriglycine
Renography
99Tm, 100MBq, 0.7mSv
90% tubular secretion, 10% filtered
why need geometric mean in dmsa
geometric mean adjusts for differential distance of kidneys from gamma camera
in patient with stone disease what level function consider nephrectomy
Depends on a number of factors including age / fitness for relative interventions, overall renal function, particular condition
<10% function usually nephrectomy
>20% renal preservation
10-20% depends on above factors
principle of radioisotope renography
Radioisotope imaging involves labelling of organic compounds with a radioactive isotope that emits gamma irradiation.
Gamma rays penetrate through tissues and get detected by a gamma camera.
principle of radioisotope renography
Radioisotope imaging involves labelling of organic compounds with a radioactive isotope that emits gamma irradiation.
Gamma rays penetrate through tissues and get detected by a gamma camera.
picture taking interval MAG 3 scanr
Images are collected onto a film at 30s intervals for the first 3 mins and then at 5 min intervals
total 40 mins
radiation dose MAG 3
0.7mSV
what is mag3 renogram represent
Relationship between supply and excretion is known as the time-activity curve aka ‘Renogram’
2/3 of MAG-3 taken up by kidney with each passage of blood through the kidney
Peak of activity is reached when MAG-3 delivery to the kidney via renal artery is equivalent to excretion
technetium 99
decay half life
daughter nuclide of
produced in a generator and extracted by
Decay half life of 6 hours- Daughter nuclide of Mo 99 by decay in a metastable state.
Produced in generator and extracted by column chromatography
half life of Cr51
27 hours
dose of MAG3 given
50-70MBq of agent is given iv (flush with saline)
how is bone scan performed
radiation dose
Injection of Tc99 Methylene Diphosphonate IV, Wait 3 hours. Gamma camera scan. AP, PA and other views PRN. 3.6mSv (equivalent to 180 CXRs and similar to an IVU).
MDP binding site
The phosphonate compounds bind to bone by chemo-adsorption to the hydroxyapatite crystal
release of gamma rays by Tc 99
Technetium 99m decays by releasing 140-kV gamma rays, which are detected by a gamma camera.
The appearance of activity on the scan usually reflects osteoblastic activity in bone.
causes of superscan
Diffuse metastatic disease Prostate carcinoma Breast carcinoma TCC Multiple myeloma Lymphoma
dose DMSA scan
0.8mSV - 1mSV
vs MAG3 0.4-0.7mSV
gamma camera
gamma rays hit scintillation crystal
which make scintillation light which is collected by photomultiplier tubes
converted to volts which make up picture
