Myocardial perfusion imaging

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Myocardial perfusion imaging
thallium-201 for the rest images (bottom rows) and Tc-Sestamibi for the stress images (top rows)
SynonymsMyocardial perfusion scintigraphy
ICD-10-PCSC22G
MeSHD055414
OPS-301 code3-704, 3-721
eMedicine2114292

Myocardial perfusion imaging or scanning (also referred to as MPI or MPS) is a

myocardium).[1]

It evaluates many heart conditions, such as

left ventricular ejection fraction (LVEF) of the heart. This scan is done in conjunction with a cardiac stress test. The diagnostic information is generated by provoking controlled regional ischemia in the heart with variable perfusion
.

Planar techniques, such as conventional

infarcted and viable myocardium.[3] The usual isotopes for such studies are either thallium-201 or technetium-99m
.

History

The history of

radioactivity. Measured over time, this sequential acquisition of radioactivity produced what was known as "circulation time". The longer the "circulation time", the weaker the heart. Blumgart's emphasis was twofold. First, radioactive substances could be used to determine cardiac physiology (function) and should be done so with the least amount of radioactivity necessary to do so. Secondly, to accomplish this task, one needs to obtain multiple counts over time.[citation needed
]

For decades no substantial work was done, until 1959. Dr.

nitroglycerin emphasized several points.[6] First, like Blumgart, he emphasized that evaluation of cardiac function required multiple measurements of change over time and these measurements must be performed under same state conditions, without changing the function of the heart in between measurements. If one is to evaluate ischemia (reductions in coronary blood flow resulting from coronary artery disease) then individuals must be studied under "stress" conditions and comparisons require "stress-stress" comparisons. Similarly, if tissue damage (heart attack, myocardial infarction, cardiac stunning or hibernation) is to be determined, this is done under "resting" conditions. Rest-stress comparisons do not yield adequate determination of either ischemia or infarction. By 1963, Dr. William Bruce, aware of the tendency of people with coronary artery disease to experience angina (cardiac chest discomfort) during exercise, developed the first standardized method of "stressing" the heart, where serial measurements of changes in blood pressure, heart rate and electrocardiographic (ECG/EKG) changes could be measured under "stress-stress" conditions. By 1965 Dr. William Love demonstrated that the cumbersome cloud chamber could be replaced by a Geiger counter, which was more practical to use. However, Love had expressed the same concern as many of his colleagues, namely that there were no suitable radioisotopes available for human use in the clinical setting.[7]

Use of thallium-201

By the mid-1970s, scientists and clinicians alike began using

thallium-201 as the radioisotope of choice for human studies.[8] Individuals could be placed on a treadmill and be "stressed" by the "Bruce protocol" and when near peak performance, could be injected with thallium-201. The isotope required exercise for an additional minute to enhance circulation of the isotope. Using nuclear cameras of the day and given the limitations of Tl-201, the first "stress" image could not be taken until 1 hour after "stress". In keeping with the concept of comparison images, the second "stress" image was taken 4 hours after "stress" and compared with the first. The movement of Tl-201 reflected differences in tissue delivery (blood flow) and function (mitochondrial activity). The relatively long half-life of Tl-201 (73 hours) forced doctors to use relatively small (74–111 MBq or 2–3 mCi) doses of Tl-201, albeit with relatively large dose exposure and tissue effects (20 mSv). The poor quality images resulted in the search for isotopes which would produce better results.[9]

The introduction of technetium-99m isotopes

By the late 1980s, two different compounds containing technetium-99m were introduced: teboroxime

sestamibi. The utilization of Tc-99m would allow higher doses (up to 1,100 MBq or 30 mCi) due to the shorter physical (6 hours) half life of Tc-99m. This would result in more decay, more scintillation and more information for the nuclear cameras to measure and turn into better pictures for the clinician to interpret.[citation needed
]

Major indications

Radiation dose

From 1993 to 2001, myocardial perfusion scans in the US increased >6%/y with "no justification".

nuclear cardiology where the evidence is most strong".[13][16]

Many radionuclides used for myocardial perfusion imaging, including

mSv).[17] The Cardiac PET tracer nitrogen-13 ammonia, though less widely available, may offer significantly reduced doses (2 mSv).[17][18][19][20] Stress-only protocols may also prove to be effective at reducing costs and patient exposure.[21]

References

  1. ^ Myocardial+Perfusion+Imaging at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
  2. PMID 23971065
    .
  3. ^ Merck manuals > Radionuclide Imaging Last full review/revision May 2009 by Michael J. Shea, MD. Content last modified May 2009
  4. ^ Blumgart HL, Yens OC. Studies on the velocity of blood flow: I. The method utilized. J Clin Investigation 1927;4:1-13.
  5. PMID 14340959
    . Retrieved 27 April 2012.
  6. ^ Gorlin R, Brachfeld N, MacLeod C. and Bopp P. Effect of nitroglycerin on the coronary circulation in patients with coronary artery disease or increased left ventricular work. Circulation 1959;19:705-18.
  7. ^ Love WD. (1965) Isotope Technics in Clinical Cardiology. Circulation 32:309-15.
  8. ISBN 9780781720076
    .
  9. PMID 19356572
    .
  10. PMID 1473653
    .
  11. PMID 24556531
    .
  12. ^
    PMID 19710480
    .
  13. ^
    PMID 15129710
    .
  14. PMID 19955531
    .
  15. ^ "Myocardial perfusion scintigraphy for the diagnosis and management of angina and myocardial infarction". NICE. 26 November 2003. Retrieved 14 December 2017.
  16. S2CID 31369868
    .
  17. ^
    PMID 21098448
    .
  18. ^ "Notes for Guidance on the Clinical Administration of Radiopharmaceuticals and use of sealed Radioactive Sources" (pdf). Department of Health. Public Health England. 22 February 2017.
  19. ^ A revised effective dose estimate for the PET perfusion tracer Rb-82, deKemp et al, J NUCL MED MEETING ABSTRACTS, 2008. 49(MeetingAbstracts_1): p. 183P-b-.
  20. ^ Radiopharmaceuticals for nuclear cardiology: radiation dosimetry, uncertainties, and risk., Stabin et al, J Nucl Med, 2008. 49(9): p. 1555-63.
  21. ^ Stress-only Nuclear Myocardial Perfusion Imaging[permanent dead link], Heston TF, Internet Med J, accessed 17-Feb-2012.
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