It’s about time we think about lowering radiation dose in obese patients too
It's about time we think about lowering radiation dose in obese patients too
Daniel A Kim 0 3
Mary Beth Farrell 0
Scott D. Jerome 0
0 Reprint requests: Mary Beth Farrell, MS, Intersocietal Accreditation Commission , Ellicott City, MD , USA
1 Intersocietal Accreditation Commission , Ellicott City, MD , USA
2 Division of Cardiovascular Medicine, University of Maryland School of Medicine , Baltimore, MD , USA
3 University of Maryland School of Medicine , Baltimore, MD , USA
Medical technology has advanced at a rapid pace,
particularly, the diagnostic imaging tools relied upon
daily to care for patients. Myocardial perfusion imaging
(MPI) uses advanced technology and
radiopharmaceuticals to detect, assess, and risk-stratify ischemic heart
disease.1,2 The level of radiation exposure from these
scans is often higher than other diagnostic imaging
procedures.3 Patients and health care providers are
increasingly more aware of and concerned about the
potential health risks associated with radiation
exposure.4 It is, therefore, prudent that the radiation dose
from diagnostic imaging scans be kept as low as possible
while maximizing image quality. Therein lies the
If we were to construct the ideal radiation reduction
strategy, it would be adaptable to patients of all ages,
body habitus, ambulatory status, and admission state.
Protocols should be flexible for both patients and
laboratories while hopefully improving workflow. Expensive
hardware and software would not be required, and there
should be associated cost savings. All of this must be
accomplished while concomitantly producing
highquality images that can be confidently used to make the
To address concerns related to radiation, the
American Society of Nuclear Cardiology (ASNC)
published several recommendations for reducing
radiation dose.5-7 Suggested approaches include utilization of
appropriate use criteria, stress-only imaging, limited use
of a dual isotope protocol, and PET imaging, where
appropriate. Other approaches rely on recent
improvements in camera hardware and software such as
highsensitivity cadmium zinc telluride (CZT) solid-state
detectors and iterative reconstruction resolution
recovery algorithms, which can allow injection of less
radiotracer and/or decrease image acquisition time.8,9
Along with specific techniques for lowering radiation
dose, the many recommendations emphasize
patientcentered imaging that tailors the imaging protocol
specifically to each patient.10-12
ASNC specifically advocated reducing radiation
exposure such that [50% of a facility’s MPI patients
receive a total effective dose B9 mSv.5 A recent study
published by Jerome et al. reviewed 5216 MPI studies
performed at 1074 Intersocietal Accreditation
Commission accredited facilities in 2012 and 2013.13 They
found most facilities were not meeting this radiation
dose goal. They reported the average effective dose was
14.9 ± 5.8 mSv, far above the B9 mSv goal. Only 1.4%
of all laboratories administered B9 mSv in [50% of
cases. Additionally, they found that only 0.4% of studies
performed were stress-only, and 7.5% of facilities
continued to use the dual isotope protocol. These findings
suggest that laboratories still encounter difficulties in
routinely lowering radiation dose effectively.
One particular struggle in reducing radiation
exposure is obtaining quality images in obese patients at a
lower radiation dose. Considering there are over 300
million obese people in the United States and with the
number growing, better options to imaging obese
patients are promptly needed.14 Increased body mass
results in photon attenuation which decreases the
signalto-noise ratio and increases scatter. The outcome is
image noise, artifacts, and nondiagnostic results.15,16
The obvious solution is to either increase image
acquisition time or increase radiopharmaceutical dose. Both
options are not without problems.
Longer acquisition time can lead to increased count
density but at the cost of patient comfort. In practice,
most patients cannot lie still for more than 20–25
minutes without moving and creating associated motion
artifacts. No known measures defining adequate count
density exist to help labs determine appropriate time per
stop or count density as camera sensitivity and
acquisition parameters vary widely.
Likewise, there are no clear guidelines for
weightbased dosing in obese patients. Most published
recommendations only suggest dosing schemes for
lighterweight patients5 or dosing using advanced technology
instead of conventional SPECT cameras.17 This issue is
so multifaceted that the authors of the 2015 European
Association of Nuclear Medicine Guidelines for MPI
state that ‘‘it is not possible to make precise
recommendations regarding injected activities as hard
evidence documenting superior results with certain
activities is not available.’’18 The most recent ASNC
SPECT Imaging Guidelines are also noncommittal with
regard to dosing strategies for obese patients.19 The
guidelines suggest, ‘‘as a strategy to be considered,’’ a
two-day protocol for patients weighing more than 250
lbs. using 18 to 30 mCi of a Tc99m tracer administered
each day. A one-day protocol can also be followed using
10 mCi of Tc99m for patients with a BMI 30 to 35 kg/
m2 or 12 mCi for patients with a BMI [35 kg/m2 for the
first dose and three times the amount used for the second
dose. The recommendations also suggest the substitution
of PET in place of SPECT imaging for overweight
patients as an option. Clearly, there is no consensus on
the best approach.
In the current issue of Journal of Nuclear
Cardiology, Oddstig et al. tackled the question of reducing
radiation dose by evaluating a linear weight-adjusted
low-dose protocol for obese patients. Based on their
prior study of a low-dose protocol for nonobese patients
using 2.5 MBq/kg body weight, they projected this
concept for patients who were obese in an attempt to
expand the 2.5 MBq/kg to all types of patients.20 In this
prospective study, patients weighing less than 110 kg
received 2.5 MBq/kg of 99Tc-tetrofosmin, while for
patients weighing 110 to 120 kg and [120 kg, a fixed
dose of 430 and 570 MBq, respectively, were used.
Images were obtained using a conventional gamma
camera with resolution recovery software or a newer
CZT cameras, with about half of the subjects imaged in
each of the two groups.
A subgroup consisting of sixteen patients with body
weights over 110 kg were resampled into a reduced
acquisition time based on a mathematical calculation
that corresponded to an administered activity of 2.5
MBq/kg. Those that received a reduced imaging time
were found to have total counts in the left ventricle that
were similar to counts from the nonobese patients who
received the same dose. Two blinded observers
measured perceived quality and found the quality between
the fixed dose and shorter imaging time to be identical.
Given these findings, Oddstig et al. concluded that the
traditional higher administered activity and prolonged
acquisition time for obese patients were not necessary to
obtain an adequate myocardial perfusion study in terms
of image quality and ischemia quantification.
This innovative dosing scheme is to be commended,
but it is not without limitations. First, the results are a
theoretical representation of a proof of concept. In the
methods, the investigators did not acquire actual images
from lower administered radiotracer doses. Count rates
were simulated using the acquired count rate; then, a
new acquisition time was calculated to correspond to the
number of counts that would have been acquired if the
administered activity was 2.5 MBq/kg.
The authors acknowledge that the study only
examined four patients with a weight of [120 kg on the
CZT camera due to positioning challenges. The overall
number of obese patients was still small at 33 patients,
and those patients had a wide range of BMIs (31 to 58
Thirdly, the investigators imaged patients using a
GE Discovery 530 CZT camera and GE Ventri
conventional camera with resolution recovery reconstruction.
Both cameras models are relatively new on the market,
utilizing state-of-the-art technology. In 2013, Bateman
et al. reported an average camera age of 7.7 ± 4.8
years.21 A recent query of the Intersocietal Accreditation
Commission database shows that the average camera age
of facilities applying for accreditation in 2015 was
11.5 ± 5.1 years. Therefore, in order for the results of
this study to apply to a majority of facilities, the results
would need to be validated on a wide variety of camera
types which are in use by most laboratories.
The proposed dosing scheme also may be limited in
terms of practicality. Administering an exact dose of
radiotracer may be problematic. Calibration of smaller
doses may limit flexibility and negatively affect the
ability to administer doses to patients who arrive late for
their study. In addition, adhesion of both Tc99m
radiopharmaceuticals to the syringe can be problematic. A
recent study suggested that 20.1% ± 8.0% of the
sestamibi dose can remain in the syringe.22 Dispensing the
hypothesized lower amount proposed by Oddstig et al.
could result in actual administered doses less than
intended and risk compromising image quality. This
could be compounded because most facilities in the
United States utilize delivered unit doses. Finally,
Jerome et al. found that most labs routinely use 10 and
30 mCi Tc99m MPI doses for all patients.13 The new
dosing scheme would require labs to obtain height and
weight and then calculate the exact dose to be ordered.
This would create a small, albeit noticeable amount of
additional work for technologists and potential loss of
flexibility. All of these practical limitations are
surmountable but would need to be considered by a
laboratory prior to implementation.
The intention of this study was to achieve a
reduction in radiation dose given to the obese patient.
With the hypothesized approach of administering a
lower dose, which the authors have shown works in
‘‘normal’’ weight patients as well as obese patients,
there is an unintended benefit of using less Tc99m
overall—even worldwide. In the recent past, we suffered
Tc99m shortages, and another shortage may gloom our
future.23 If the author’s strategy proves to be effective
and adopted widely, further study of the amount of
Tc99m usage throughout the world needs to be looked at
as this may have a major impact on the supply/demand
and future generator production.
In summary, before the hypothesized, 2.5 MBq/kg
administration schedule can be added to the arsenal of
radiation reduction techniques, further dedicated
research is needed to confirm the practicality of this
approach, the maintenance of image quality and
accuracy. Studies need to be performed actually
administering the proposed individual weight-based
dose and overcoming the challenges cited above. The
investigators are to be congratulated for ‘‘thinking
outside of the box’’ and proposing a novel method to lower
radiation dose, especially in obese patients where there
is a performance gap. In their study, they were mindful
of the effect of lower doses on image quality, reinforcing
that image quality must never be jeopardized at the
expense of lowering dose. Their proposed dosing
strategy follows the principles of patient-centered imaging
and is another step toward the goal of personalized
medicine. The results of this study appear to be
promising in reducing radiation dose for obese patients,
and research on additional strategies to lower and
standardize radiation doses in obese patients is encouraged.
1. Klocke FJ , Baird MG , Lorell BH , et al. ACC/AHA/ASNC guidelines for the clinical use of cardiac radionuclide imagingexecutive summary: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (ACC/AHA/ASNC Committee to Revise the 1995 Guidelines for the Clinical Use of Cardiac Radionuclide Imaging) . Circulation 2003 ; 108 : 1404 - 18 .
2. Holly TA , Abbott BG , Al-Mallah M , et al. Single photon-emission computed tomography . J Nucl Cardiol 2010 ; 17 : 941 - 73 .
3. Chen J , Einstein AJ , Fazel R , et al. Cumulative exposure to ionizing radiation from diagnostic and therapeutic cardiac imaging procedures: a population-based analysis . J Am Coll Cardiol 2010 ; 56 : 702 - 11 .
4. Fazel R , Shaw LJ . Radiation exposure from radionuclide myocardial perfusion imaging: concerns and solutions . J Nucl Cardiol 2011 ; 18 : 562 - 5 .
5. Cerqueira MD , Allman KC , Ficaro EP , et al. Recommendations for reducing radiation exposure in myocardial perfusion imaging . J Nucl Cardiol 2010 ; 17 : 709 - 18 .
6. Dorbala S , Blankstein R , Skali H , et al. Approaches to reducing radiation dose from radionuclide myocardial perfusion imaging . J Nucl Med 2015 ; 56 : 592 - 9 .
7. Fazel R , Gerber TC , Balter S , et al. Approaches to enhancing radiation safety in cardiovascular imaging: a scientific statement from the American Heart Association . Circulation 2014 ; 130 : 1730 - 48 .
8. Pagnanelli R , Borges-Neto S . Technical aspects of resolution recovery reconstruction . J Nucl Cardiol 2016 ; 23 : 149 - 52 .
9. Einstein AJ , Blankstein R , Andrews H , et al. Comparison of image quality, myocardial perfusion, and left ventricular function between standard imaging and single-injection ultra-low-dose imaging using a high-efficiency SPECT camera: the MILLISIEVERT study . J Nucl Med 2014 ; 55 : 1430 - 7 .
10. Einstein AJ , Berman DS , Min JK , et al. Patient-centered imaging: shared decision making for cardiac imaging procedures with exposure to ionizing radiation . J Am Coll Cardiol 2014 ; 63 : 1480 - 9 .
11. Walsh MN , Bove AA , Cross RR , et al. ACCF 2012 health policy statement on patient-centered care in cardiovascular medicine: a report of the American College of Cardiology Foundation Clinical Quality Committee . J Am Coll Cardiol 2012 ; 59 : 2125 - 43 .
12. Depuey EG , Mahmarian JJ , Miller TD , et al. Patient-centered imaging . J Nucl Cardiol 2012 ; 19 : 185 - 215 .
13. Jerome SD , Tilkemeier PL , Farrell MB , Shaw LJ . Nationwide laboratory adherence to myocardial perfusion imaging radiation dose reduction practices: a report from the intersocietal accreditation commission data repository . JACC Cardiovasc Imaging 2015 ; 8 : 1170 - 6 .
14. Duvall WL , Croft LB , Corriel JS , et al. SPECT myocardial perfusion imaging in morbidly obese patients: image quality, hemodynamic response to pharmacologic stress, and diagnostic and prognostic value . J Nucl Cardiol 2006 ; 13 : 202 - 9 .
15. Wackers FJ . Cardiac single-photon emission computed tomography myocardial perfusion imaging: finally up to speed? J Am Coll Cardiol 2010 ; 55 : 1975 - 8 .
16. Burrell S , MacDonald A. Artifacts and pitfalls in myocardial perfusion imaging . J Nucl Med Technol 2006 ; 34 : 193 - 211 .
17. Marcassa C , Zoccarato O , Calza P , Campini R . Temporal evolution of administered activity in cardiac gated SPECT and patients' effective dose: analysis of an historical series . Eur J Nucl Med Mol Imaging 2013 ; 40 : 325 - 30 .
18. Verberne HJ , Acampa W , Anagnostopoulos C , et al. EANM procedural guidelines for radionuclide myocardial perfusion imaging with SPECT and SPECT/CT: 2015 revision . Eur J Nucl Med Mol Imaging 2015 ; 42 : 1929 - 40 .
19. Henzlova MJ , Duvall WL , Einstein AJ , Travin MI , Verberne HJ . ASNC imaging guidelines for SPECT nuclear cardiology procedures: Stress, protocols, and tracers . J Nucl Cardiol 2016 ; 23 : 606 - 39 .
20. Oddstig J , Hedeer F , Jogi J , Carlsson M , Hindorf C , Engblom H . Reduced administered activity, reduced acquisition time, and preserved image quality for the new CZT camera . J Nucl Cardiol 2013 ; 20 : 38 - 44 .
21. Patil H , Abdallah M , Bateman T. Correlates between camera age, patient volume, and laboratory accreditation: A snapshot of equipment utilization in the practice of nuclear cardiology in the US . J Nucl Med 2013 ; 54 : 516 .
22. Swanson TN , Troung DT , Paulsen A , Hruska CB , O'Connor MK . Adsorption of 99mTc-sestamibi onto plastic syringes: evaluation of factors affecting the degree of adsorption and their impact on clinical studies . J Nucl Med Technol 2013 ; 41 : 247 - 52 .
23. Thomas GS , Maddahi J. The technetium shortage . J Nucl Cardiol 2010 ; 17 : 993 - 8 .