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NM > Molecular Imaging - Kidneys > Flashcards

Molecular Imaging - Kidneys Flashcards

1
Q

What do we need dynamic imaging for?

How do you do it?

A

To show the changes in rp distribution in time

  • Accquire multiple images in frame mode
  • Frame rate is determined by speed of underlying physiological process
  • Pharmaceutical chosen for organ of interest
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2
Q

What do kidneys do?

A

Filter the blood to extract metabolic waste products and regulate water/electrolyte balance

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3
Q

Physiological processes in Kidney

A
  • Glomerular filtration in renal corpuscule filters water and small molecules into Bowmans capsule (20%)
  • Fluid passes into proximal tubulus where slective reabsorption takes place of water and some other molecules
  • Active secretion (80%)- waste materials secreted into filtrate by into collecting tubule and into renal pelvis artery
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4
Q

From an Imaging Perspective what are the three main phases of kidney function?

A
  1. Perfusion - 0-30s after IV injections
  2. Filtration/Uptake - 1-5mins
  3. Excretion - >5mins
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5
Q

Acquisition Requirements: Frame Rate

A

Must be appropriate for speed of underlying physiological process Usually image for 30 minutes in adults and 40 minutes in paediatrics.

  1. Perfusion - 1 second images for 60 seconds
  2. Filtration/excretion 20/30 second images for 30-40 minutes.
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6
Q

Acquisition Requirements - Collimator Choice

A
  • Rapid imaging = low number of counts from each frame (perfusion phase), here sensitivity is more important than resolution. LEAP collimator.
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7
Q

Acquisition Requirements - Collimator Choice

A

Use whatever is appropriate for FWHM of LEAP collimator

  • Pixel size should be ≤ FWHM/3. FWHM of LEAP collimator is ~9m, hence pixel size ≤ 3mm
  • Field of View (FOV) ~ 390mm, FOV/pixel size ~ 130, hence required matrix size is 128x128
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8
Q

3 RPs for renal imaging?

Which one is used for static only?

A
  • Tc99m DTPA
  • Tc99m MAG3
  • Tc99m DMSA (used for static imaging only)
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9
Q

Tc99m DTPA ( Diethylene triamine penta-acetic acid)

What do you use it for?

Activity

Advantages & Disadvantages

A
  • Excreted by Glomerular filtration (98%), hence may be used to determine glomerular filtration rate.
  • Not bound in kidney, but low extraction efficiency (GF is 20% total filtration)
  • Adult dose 200MBq
  • Effective Radiation Dose 1.3mSv (higher than MAG3)
  • Low cost (~ £10 per kit)
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10
Q

Tc99m MAG3 (Mercaptoacetyltriglycine)

What do you use it for?

Activity

Advantages & Disadvantages

A
  • Useful for patients with suspected poor renal function and for paediatrics. Excreted by tubular secretion (98%). Not bound in kidney, hence high extraction efficiency (80% )
  • Adult dose 100MBq
  • Effective Radiation Dose 0.7mSv (lower than DTPA)
  • High cost (~ £100 per kit)
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11
Q

2 main and 4 lesser clinical applications for renograms

A
  1. Assessment of relative renal function (including pre-op/post-op assessment)
  2. Urinary tract obstruction
  3. Glomerular filtration rate
  4. Renal vascular disease
  5. Renal failure
  6. After transplantation
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12
Q

Relative Renal Function

How do you prepare patient?

What do you administer?

How do you image?

A

Drink 0.5L water, Void before imaging.

Iv injection at start, Adult dose 200MBq 99mTc DTPA or 100MBq MAG3.

Images Supine with LEAP coll. Accquire 60x1s frames, 58x30s frames, patient void, 3min post-static post micturation (kidney releases to bladder)

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13
Q

Relative Renal Function

First step before processing?

A

First step is to check for movement, 30min scan, corect for this and allign images with motion correction. Draw ROIs and allign kidneys to ROI in each frame.

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14
Q

Relative Renal Function

How do you make time-activity curve?

A

Create time activity curve from images: draw ROIs over kidnets, heart, bladder & background. Create curves by plotting counts in each region against time. QUANTITATIVE

Showing comparitive function of kidneys - perfusion curve

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15
Q

Relative Renal Function

Background correction

when do you need to do it?

why do you need to do it?

How do you do it?

A
  • Perfusion curves don’t need to be background corrected as RP is pretty much still in arteries. After, RP is present in other organs as well ask kidneys e.g. liver
  • Planar images compress 3D into 2D image, so some counts in the kidney region will have come from over and underlying anatomy.
  • Correct for this to remove counts from ROI from anything other than the kidney.
  • Best way to do it is to use region close to kidney that avoids other organs e.g. ureters. 1 region for each kidney. or single ROI in the middle
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16
Q

Relative Renal Function

Background correction Maths

A
  • Left kidney ROI area = LKA (const)
  • Left kidney ROI counts = LKAC (varies in time)
  • Left bkgrnd ROI area = LBA (const)
  • Left bkgrnd ROI counts = LBAC (varies in time)
  • Background Corrected Counts in Left Kidney ROI = CLKAC (varies with time)
    • CLKAC = LKAC – ( LBAC * LKA/LBA)

Counts in left kidney - background counts weighted by the relative area of the two ROIs.

17
Q

Describe the 3 quantitative things you can get from relative renogram curves

A

Relative Renal Function

  • Compare function/uptake of each kidney by integrating the background corrected curves from 1-3mins.
  • Relative function of each kidney is a percentage of total kidney function. Right kidney % = right counts (bgd corrected) /total counts (bgd correctd) * 100
  • Normal range 43% to 57%

Time to peak

  • Clearence of RP fro mkidney depends on transit time through the kidney. At peak of curve, uptake and clearence erach equilibrium. After eqm, amount of RP in kidneys decreases. Normal range for time-to-peak is 2-5mins

Transit time

  • Whole kidney tansit time - time for bolus of RP to pass through kidey and renal pelvis artery
  • Parenchymal transit time - without renal pelvis
  • Transit times obtained via deconvolution:
    • O(t) = I(t) * R(t)
    • Renal function curve (renogram) = input curve (use heart curve as bolus of activity) * retention function (passage through the kidney & gives transit time.
    • I(t) & O(t) are known, deconvolve to get retention function R(t)
18
Q

Unirary tract obstruction:

Aim of exam

A

pelvi-ureteric junction obstruction. Need to dstinguish between true and non-obstructive dilaton of the renal pelvis artery.

Use a diuretic to increase flow rate of uring and assess change in rate of drainage.

19
Q

Unirary tract obstruction:

what do we measure?

What are the possible outcomes?

A
  • Plot time-activity curves in real time.
  • If TACs do not show spontateous clearence after 10 mins, administer 20mg of diuretic IV.
  • If clearence curves post-diuretic drop to half peak within 10 mins (normal)
  • If half-time drainage is longer than 10 mins (true obstruction of renal pelvis)

NM (8 decks)

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