|
 |
|
LETTER TO EDITOR |
|
|
|
| Year : 2011 | Volume
: 36
| Issue : 4 | Page : 239-240 |
| |
On "ruby" in myocardial perfusion imaging
Dilip Gude
Department of Internal Medicine, Medwin Hospital, Nampally, Hyderabad, Andhra Pradesh - 500 001, India
| Date of Web Publication | 18-Nov-2011 |
Correspondence Address:
Dilip Gude
Department of Internal Medicine, AMC, 3rd Floor, Medwin Hospital, Chirag Ali lane, Nampally, Hyderabad, Andhra Pradesh - 500 001
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/0971-6203.89975
How to cite this article:
Gude D. On "ruby" in myocardial perfusion imaging. J Med Phys 2011;36:239-40 |
Sir,
I would like to comment on rubidium (Rb)-82 positron emission tomography (PET) in myocardial perfusion imaging. 82 Rb PET-CT is state of the art in quantifying myocardial blood flow (MBF) and it also gives important prognostic information apart from risk stratification and according management. 3D 82 Rb-PET shows highly reproducible same-day repeated measurements of data acquisition of MBF at rest and is sensitive to detect small, serial changes in rest MBF. [1] MBF thus measured is known to correlate over a wide range of flows with 2D 15 O-water PET as standard MBF measurements. [2] The perfusion patterns of stress 82 Rb-PET using regadenoson also correlate highly with the current dipyridamole imaging protocol. Left ventricular ejection fraction reserve during dipyridamole or regadenoson 82 Rb-PET is inversely related to ischemic burden and is a marker of multivessel CAD. [3] These observations are known to correspond clinically too as depicted in a study where dynamic 82 Rb measurements provided estimates of MBF (as tested by radiolabelled microspheres) in stunned and acutely and chronically infarcted tissue at rest and during hyperemia. [4] Predictors of a lower stress/rest MBF ratio (with an apparently normal 82 Rb-PET) are age, smoking, and coronary artery calcium scoring (CACS) > 400, diabetes, hypertension, and lower BMI. [5] 82 Rb is also known to gauge endothelial dysfunction. MBF measurements with 82 Rb detected coronary endothelial dysfunction in smokers comparable to 15 O-water PET (cold-pressor test). [6]
82 Rb-PET is shown to improve the cardiac-death risk stratification in coronary artery disease (CAD) patients. In a rest-stress 82 Rb PET MPI (myocardial perfusion imaging) the size of rest, and stress-induced perfusion defects measured in percentage of the left ventricular (LV) myocardium, grouped into 0%, 0-5%, 5-10%, 10-20%, and >20% pointed to annual cardiac mortality rates across stress perfusion defect size as 0.4%, 0.9%, 1.0%, 2.2%, and 3.2% respectively. [7] 82 Rb-PET MPI reclassified 15% of individuals into more appropriate cardiac death risk strata along with the reclassification of intermediate (36%) and high (30%) pre-PET risk groups. [7] In a low-risk chest pain population, cardiac 82 Rb-PET had true-positive cardiac catheterization rates comparable to prior studies of SPECT sestimibi imaging and coronary CTA imaging. [8] Likewise serial 82 Rb-PET MPI shows that for each 5% improvement in defect size (after revascularization) between scans, there is a 20% improvement in risk of both all-cause and cardiac-specific mortality. [9]
82 Rb-PET/CT also helps gauge the incidence of major adverse cardiac events (MACE) such as cardiac death, myocardial infarction, revascularization or hospitalization for cardiac-related event. In a study on patients with known or suspected CAD who underwent both a rest and adenosine stress cardiac 82 Rb PET/CT, annualized MACE rate was higher in those with ischemia compared to those without ischemia (60% vs. 8%). Those with lowest myocardial flow reserve (MFR) tertile (MFR<1.7) had higher MACE rate than the two highest tertiles (44% vs. 9% and 12%). [10] Cross sectional area (CSA) measurement with computed tomography angiography (CTA) of ≤1.35 mm 2 has a sensitivity of 91% and specificity of 54% for predicting 82 Rb MFR < 2; and a sensitivity of 64% and a specificity of 91% for predicting severely impaired 82 Rb MFR (< 1.5). [11]
82 Rb is easily available, has a fixed cost, enables high patient throughput with faster and easier qualitative evaluation of MBF and can be scheduled in emergencies unlike 13 N ammonia. Although 13 N ammonia may get better resolution than 82 Rb (owing to lower mean positron range), the logistical burden of coordination and the requirement of an onsite cyclotron apart from necessitating synchronization by numerous staff may limit its use. [12] 15 O-water also has high patient throughput, very low radiation burden and is generally considered a better MBF tracer (metabolically inert, freely diffusible, complete first-pass extraction and absence of washout in scar tissue) but it has low contrast between myocardium and blood in dynamic images (low signal-to-noise ratios of scans) and requires kinetic analysis and an on-site cyclotron. [13]
82 Rb is not without limitations. Being an uptake tracer, it might not differentiate between viable myocardium and scar tissue. Its low uptake and that it is not linearly dependent on MBF may lead to underestimation of MBF warranting high correction factors. These correction factors extrapolated from animal models may be inaccurate in humans and they may also increase noise levels. Additionally active uptake by the cell, might cause the several pathophysiological processes influence 82 Rb. [13] Concerns of contamination with radioactive elements have also been raised against 82 Rb especially after the documented incident of radiation exposure of about 90 mSv (normally 2.8 mSv) in two patients. Investigation pointed to contamination of 82 Rb (CardioGen-82) with strontium ( 82 Sr and 85 Sr). [14] Although it may be an isolated event, better/reliable generator performance and monitoring for such radiation activity are warranted.
82 Rb PET is certainly an invaluable tool in tracking CAD and guiding therapeutic management for risk minimization.
 References | |  |
| 1. | Manabe O, Yoshinaga K, Katoh C, Naya M, Chiba S, Klein R, et al. Repeatability of myocardial blood flow measurements with 3D data acquisition using Rubidium-82 PET. J Nucl Med 2010;51(Suppl 2):101. 
|
| 2. | Manabe O, Yoshinaga K, Katoh C, Naya M, Chiba S, Klein R, et al. Quantification of myocardial blood flow with Rubidium-82 3D-data acquisition - Comparison with O-15 labeled water dynamic PET. J Nucl Med 2010;51(Suppl 2):156.
|
| 3. | Hsiao E, Ali B, Blankstein R, Kwong R, Di Carli M, Dorbala S. A pilot study of left ventricular ejection fraction reserve during regadenoson rubidium-82 myocardial perfusion imaging and the magnitude of ischemia and CAD. J Am Coll Cardiol 2010;55;A66.E617.
|
| 4. | Lekx KS, deKemp RA, Beanlands RS, Wisenberg G, Wells RG, Stodilka RZ, et al. Quantification of regional myocardial blood flow in a canine model of stunned and infarcted myocardium: Comparison of rubidium-82 positron emission tomography with microspheres. Nucl Med Commun 2010;31:67-74.
[PUBMED] [FULLTEXT] |
| 5. | Rader VJ, Courter SA, Case JA, Kennedy KF, Bateman TM. Abstract 14503: Prevalence and Correlates of Impaired Myocardial Blood Flow Reserve in Patients With Normal Myocardial Perfusion Rubidium-82 Positron Emission Tomography. Circulation 2010;122(Meeting Abstract Supplement):A14503.
|
| 6. | Yoshinaga K, Manabe O, Katoh C, Chen L, Klein R, Naya M, et al. Quantitative analysis of coronary endothelial function with generator-produced 82Rb PET: Comparison with 15O-labelled water PET. Eur J Nucl Med Mol Imaging 2010;37:2233-41.
[PUBMED] [FULLTEXT] |
| 7. | Williams BA, Merhige ME, LaMonte MJ, Leonard D, Greene R, Trevisan M, et al. Abstract 323: The Incremental Prognostic Value of Myocardial Perfusion Parameters as Measured by Rubidium-82 Positron Emission Tomography. Circulation 2009;120:S319-20.
|
| 8. | Osborne AD, Moore B, Ross MA, Pitts SR. The feasibility of Rubidium-82 positron emission tomography stress testing in low-risk chest pain protocol patients. Crit Pathw Cardiol 2011;10:41-3.
[PUBMED] [FULLTEXT] |
| 9. | Merhige M, Williams BA. Abstract 21379: The Prognostic Value of Longitudinal Change in Myocardial Perfusion Defect Size as Measured by Rubidium-82 Positron Emission Tomography. Circulation 2010;122:A21379.
|
| 10. | Fahrad H, Dunet V, Soubeyran V, Camus F, Allenbach G, Prior JO. Abstract 20265: Myocardial Blood Flow Quantification with Rubidium-82 Cardiac PET has Incremental Prognostic Value in Patients with Known or Suspected Coronary Artery Disease. Circulation 2010;122:A20265.
|
| 11. | Ziadi MC, Galiwango P, DeKemp RA, Yam Y, Ruddy TD, Beanlands RS, et al. Validation of an anatomic measure of coronary stenosis with computed tomography angiography to predict hemodynamic significance of disease defined by flow quantification using rubidium-82 positron emission tomography. J Am Coll Cardiol 2010;55;A74.E696.
|
| 12. | Berger KL (2007). Discussions in PET Imaging. [Last retrieved on 2011 Sep 22]. Available from: http://imaging.ubmmedica.com/dimag/dpi/ge/pdf/dpi655.pdf [Last accessed on 2011 Aug 17].
|
| 13. | Harms HJ, Lammertsma AA, Lubberink M, Knaapen P, De Haan S. Quantitative myocardial blood flow imaging using PET/CT. Medicamundi 2010;54:32-40.
|
| 14. | U.S. Food and Drug Administration (2011). FDA Drug Safety Communication: FDA alerts healthcare professionals to stop performing heart scans with CardioGen-82 due to potential for increased radiation exposure in patients. [Last retrieved on 2011 Sep 21]. Available from: http://www.fda.gov/Drugs/DrugSafety/ucm265278.htm [Last accessed on 2011 Aug 17].
|
|
|
|
|
|
|
|
|
