Blood volume determination, a nuclear medicine test in evolution

Pressure-Volume Profiles in Heart Failure Across Sexes and Phenotypes

Studies have shown poor correlation between intra-cardiac pressures and blood volume (BV) measurements including HF. The impact of sex and left ventricular ejection fraction (LVEF) on this relationship has not been studied. We obtained pressure (pulmonary artery diastolic pressure (PADP)) and volume (total blood volume (TBV) and estimated stress blood volume (eSBV)) measurements from HF patients at the time of CardioMEMS implantation. A total of 20 patients were included. There was no significant difference between PADP, TBV, and eSBV between sexes. There was only a moderate correlation between PADP and eSBV in men but not in women or with TBV in both sexes. HFrEF had higher PADP and eSBV than HFpEF. There was a consistent lack of correlation between PADP and both TBV and eSBV. Further studies evaluating mid- to long-term implications of pressure-volume profiles as well as changes following decongestion therapy are warranted to better understand the pressure-volume interplay and determine appropriate decongestion strategy for each pressure-volume phenotype.

[Discontinuation of Chromium-51 for clinical use: What are the possible alternatives for radiopharmacies and nuclear medicine departments?]

OBJECTIVES

Last October, the nuclear medicine departments were informed of the closure of the chromium-51 production line for clinical use. This radionuclide has different diagnostic indications in nephrology and hematology. It was therefore essential to set up alternative exploration protocols to overcome this production stoppage.

METHODS

Chromium-51 EDTA has been replaced by technetium-99m DTPA for the determination of glomerular filtration rates. Sodium chromate was substituted by sodium pertechnetate for the determination of globular volumes. A retrospective analysis of the chromium-51 data was performed followed by a prospective study, from January to December 2019 for technetium tracers.

RESULTS

One hundred and forty-four patients were included in the study. Forty-two EDTA-⁵¹Cr and 30 DTPA-^99mTc exams were conducted and compared. There were no significant differences between the methods used to assess renal function (P=0.355). For the determination of blood cell and plasma volumes, 47 tests with ⁵¹Cr and ¹²⁵I and 25 tests with ^99mTc and ¹²⁵I were performed and compared. There were no significant differences in the determination of total (P=0.325) and globular (P=0.148) volumes.

CONCLUSIONS

The study carried out shows that there is no significant difference between the results obtained with chromium-51 and technetium tracers. As a result, clinical activity was maintained in good conditions.

Ultrafiltration in Acute Heart Failure

Congestion is the predominant cause of more than 1 million annual heart failure hospitalisations and recurrent fluid overload predicts poor outcomes. Unresolved congestion trumps serum creatinine increases in predicting adverse heart failure outcomes. No pharmacological approach for acute heart failure has reduced these deleterious consequences. Simplified ultrafiltration devices permit fluid removal in lower acuity hospital settings, but results regarding safety and efficacy have been variable. However, adjustment of ultrafiltration rates to patients’ vital signs and renal function has been associated with more effective decongestion and fewer heart failure events. Many aspects of ultrafiltration, including patient selection, fluid removal rates, venous access, prevention of therapy-related complications and costs, require further investigation.

Bench to Bedside: Albumin Binders for Improved Cancer Radioligand Therapies

Radioligand therapy (RLT) relies on the use of pharmacophores to selectively deliver ionization energy to cancers to exert its tumoricidal effects. Cancer cells that are not directly targeted by a radioconjugate remain susceptible to RLT because of the crossfire effect. This is significant given the inter- and intra-heterogeneity of tumors. In recent years, reversible albumin binders have been used as simple "add-ons" for radiopharmaceuticals to modify pharmacokinetics and to enhance therapeutic efficacy. In this Review, we discuss recent advances in albumin binder platforms used in RLT, with an emphasis on 4-( p-iodophenyl)butyric acid and Evans blue derivatives. We focus on four biological systems pertinent to oncology that utilize this class of compounds: folate receptor, integrin αvβ3, somatostatin receptor, and prostate-specific membrane antigen. Finally, we offer our perspectives on albumin binders for RLT, highlighting future areas of research that will help propel the technology further for clinical use.

Blood volume measurement using cardiovascular magnetic resonance and ferumoxytol: preclinical validation

BACKGROUND

The hallmark of heart failure is increased blood volume. Quantitative blood volume measures are not conveniently available and are not tested in heart failure management. We assess ferumoxytol, a marketed parenteral iron supplement having a long intravascular half-life, to measure the blood volume with cardiovascular magnetic resonance (CMR).

METHODS

Swine were administered 0.7 mg/kg ferumoxytol and blood pool T1 was measured repeatedly for an hour to characterize contrast agent extraction and subsequent effect on Vblood estimates. We compared CMR blood volume with a standard carbon monoxide rebreathing method. We then evaluated three abbreviated acquisition protocols for bias and precision.

RESULTS

Mean plasma volume estimated by ferumoxytol was 61.9 ± 4.3 ml/kg. After adjustment for hematocrit the resultant mean blood volume was 88.1 ± 9.4 ml/kg, which agreed with carbon monoxide measures (91.1 ± 18.9 ml/kg). Repeated measurements yielded a coefficient of variation of 6.9%, and Bland-Altman repeatability coefficient of 14%. The blood volume estimates with abbreviated protocols yielded small biases (mean differences between 0.01-0.06 L) and strong correlations (r2 between 0.97-0.99) to the reference values indicating clinical feasibility.

CONCLUSIONS

In this swine model, ferumoxytol CMR accurately measures plasma volume, and with correction for hematocrit, blood volume. Abbreviated protocols can be added to diagnostic CMR examination for heart failure within 8 min.

Evans Blue Dye: A Revisit of Its Applications in Biomedicine

Evans blue (EB) dye has owned a long history as a biological dye and diagnostic agent since its first staining application by Herbert McLean Evans in 1914. Due to its high water solubility and slow excretion, as well as its tight binding to serum albumin, EB has been widely used in biomedicine, including its use in estimating blood volume and vascular permeability, detecting lymph nodes, and localizing the tumor lesions. Recently, a series of EB derivatives have been labeled with PET isotopes and can be used as theranostics with a broad potential due to their improved half-life in the blood and reduced release. Some of EB derivatives have even been used in translational applications in clinics. In addition, a novel necrosis-avid feature of EB has recently been reported in some preclinical animal studies. Given all these interesting and important advances in EB study, a comprehensive revisiting of EB has been made in its biomedical applications in the review.

Extracorporeal Ultrafiltration for Fluid Overload in Heart Failure: Current Status and Prospects for Further Research

More than 1 million heart failure hospitalizations occur annually, and congestion is the predominant cause. Rehospitalizations for recurrent congestion portend poor outcomes independently of age and renal function. Persistent congestion trumps serum creatinine increases in predicting adverse heart failure outcomes. No decongestive pharmacological therapy has reduced these harmful consequences. Simplified ultrafiltration devices permit fluid removal in lower-acuity hospital settings, but with conflicting results regarding safety and efficacy. Ultrafiltration performed at fixed rates after onset of therapy-induced increased serum creatinine was not superior to standard care and resulted in more complications. In contrast, compared with diuretic agents, some data suggest that adjustment of ultrafiltration rates to patients’ vital signs and renal function may be associated with more effective decongestion and fewer heart failure events. Essential aspects of ultrafiltration remain poorly defined. Further research is urgently needed, given the burden of congestion and data suggesting sustained benefits of early and adjustable ultrafiltration.

Potential Applications of Using 68Ga-Evans Blue PET/CT in the Evaluation of Lymphatic Disorder: Preliminary Observations

Purpose

Potentials of ⁶⁸Ga-NEB as a PET tracer in the evaluation of a variety of lymphatic drainage disorders were analyzed.

Methods

⁶⁸Ga-NEB was injected subcutaneously, and the PET/CT images were acquired in 13 patients with different suspected lymphatic drainage abnormality. The ⁶⁸Ga-NEB PET/CT findings were compared with ^99mTc-SC lymphoscintigraphy.

Results

⁶⁸Ga-NEB activity could be clearly observed in the lymphatic route on the PET/CT images from all the patients. In 5 (38.5%) of 13 patients tested, ⁶⁸Ga-NEB PET/CT provided more information than the ^99mTc-SC lymphoscintigraphy.

Conclusions

⁶⁸Ga-NEB PET/CT can be used as an alternative of ^99mTc-SC lymphoscintigraphy in the evaluation of lymphatic disorders, which enables fast results and might be more accurate than the conventional ^99mTc-SC lymphoscintigraphy.

Markers for blood-brain barrier integrity: how appropriate is Evans blue in the twenty-first century and what are the alternatives?

In recent years there has been a resurgence of interest in brain barriers and various roles their intrinsic mechanisms may play in neurological disorders. Such studies require suitable models and markers to demonstrate integrity and functional changes at the interfaces between blood, brain, and cerebrospinal fluid. Studies of brain barrier mechanisms and measurements of plasma volume using dyes have a long-standing history, dating back to the late nineteenth-century. Their use in blood-brain barrier studies continues in spite of their known serious limitations in in vivo applications. These were well known when first introduced, but seem to have been forgotten since. Understanding these limitations is important because Evans blue is still the most commonly used marker of brain barrier integrity and those using it seem oblivious to problems arising from its in vivo application. The introduction of HRP in the mid twentieth-century was an important advance because its reaction product can be visualized at the electron microscopical level, but it also has limitations. Advantages and disadvantages of these markers will be discussed together with a critical evaluation of alternative approaches. There is no single marker suitable for all purposes. A combination of different sized, visualizable dextrans and radiolabeled molecules currently seems to be the most appropriate approach for qualitative and quantitative assessment of barrier integrity.

Dose correction for post-contrast T1 mapping of the heart: the MESA study

Post-contrast myocardial T1 (T1(myo,c)) values have been shown to be sensitive to myocardial fibrosis. Recent studies have shown differences in results obtained from T1(myo,c) and extracellular volume fraction (ECV) with respect to percentage fibrosis. By exploring the relationship between blood plasma volume and T1(myo,c), the underlying basis for the divergence can be explained. Furthermore, dose administration based on body mass index (BMI), age and gender can mitigate the divergence in results. Inter-subject comparison of T1(myo,c) required adjustment for dose (in mmol/kg), time and glomerular filtration rate. Further adjustment for effective dose based on lean muscle mass reflected by blood/plasma volume was performed. A test case of 605 subjects from the MESA study who had undergone pre- and post-contrast T1 mapping was studied. T1(myo,c) values were compared between subjects with and without metabolic syndrome (MetS), between smoking and non-smoking subjects, and subjects with and without impaired glucose tolerance, before and after dose adjustment based on plasma volume. Comparison with ECV (which is dose independent), pre-contrast myocardial T1 and blood normalized myocardial T1 values was also performed to validate the correction. There were significant differences in T1(myo,c) (post plasma volume correction) and ECV between current and former smokers (p value 0.017 and 0.01, respectively) but not T1(myo,c) prior to correction (p = 0.12). Prior to dose adjustment for plasma volume, p value was <0.001 for T1(myo,c) between MetS and non-MetS groups and was 0.13 between subjects with and without glucose intolerance; after adjustment for PV, p value was 0.63 and 0.99. Corresponding ECV p values were 0.44 and 0.99, respectively. Overall, ECV results showed the best agreement with PV corrected T1(myo,c) (mean absolute difference in p values = 0.073) and pre-contrast myocardial T1 in comparison with other measures (T1(myo,c( prior to correction, blood/plasma T1 value normalized myocardium). Weight-based contrast dosing administered in mmol/kg results in a bias in T1 values which can lead to erroneous conclusions. After adjustment for lean muscle mass based on plasma volume, results from T1(myo,c) were in line with ECV derived results. Furthermore, the use of a modified equivalent dose adjusted for BMI, age, sex and hematocrit can be adopted for quantitative imaging.