Radiation dosimetry of 82Rb in humans under pharmacologic stress

(82)Rb is used with PET for cardiac perfusion studies. Using human biokinetic measurements, in vivo, we recently reported on the resting-state dosimetry of this agent. The objective of this study was to obtain (82)Rb dose estimates under stress.

METHODS

(82)Rb biokinetics were obtained in 10 healthy volunteers (5 male, 5 female; mean age ± SD, 33 ± 10 y; age range, 18-50 y) using whole-body PET/CT. The 76-s half-life of (82)Rb and the corresponding need for pharmacologic vasodilation require that all imaging be completed within 10 min. To accommodate these constraints, while acquiring the data needed for dosimetry we used the following protocol. First, a whole-body attenuation correction CT scan was obtained. Then, a series of 3 whole-body PET scans was acquired after a single infusion of 1.53 ± 0.12 GBq of (82)Rb at rest. Four minutes after the infusion of a 0.56 mg/kg dose of the vasodilator, dipyridamole, 3 serial whole-body PET scans were acquired after a single infusion of 1.50 ± 0.16 GBq of (82)Rb under stress. The time-integrated activity coefficient (TIAC) for stress was obtained by scaling the mean rest TIAC obtained from our previous rest study by the stress-to-rest TIAC ratio obtained from the rest-stress measurements described in this report.

RESULTS

The highest mean organ-absorbed doses under stress were as follows: heart wall, 5.1, kidneys, 5.0, lungs, 2.8, and pancreas, 2.4 μGy/MBq (19, 19, 10.4, and 8.9 mrad/mCi, respectively). The mean effective doses under stress were 1.14 ± 0.10 and 1.28 ± 0.10 μSv/MBq using the tissue-weighting factors of the International Commission on Radiological Protection, publications 60 and 103, respectively.

CONCLUSION

Appreciable differences in source-organ biokinetics were observed for heart wall and kidneys during stress when compared with the previously reported rest study. The organ receiving the highest dose during stress was the heart wall. The mean effective dose calculated during stress was not significantly different from that obtained at rest.

Human biodistribution and radiation dosimetry of 82Rb

Prior estimates of radiation-absorbed doses from (82)Rb, a frequently used PET perfusion tracer, yielded discrepant results. We reevaluated (82)Rb dosimetry using human in vivo biokinetic measurements.

METHODS

Ten healthy volunteers underwent dynamic PET/CT (6 contiguous table positions, each with separate (82)Rb infusion). Source organ volumes of interest were delineated on the CT images and transferred to the PET images to obtain time-integrated activity coefficients. Radiation doses were estimated using OLINDA/EXM 1.0.

RESULTS

The highest mean absorbed organ doses (μGy/MBq) were observed for the kidneys (5.81), heart wall (3.86), and lungs (2.96). Mean effective doses were 1.11 ± 0.22 and 1.26 ± 0.20 μSv/MBq using the tissue-weighting factors of the International Commission on Radiological Protection (ICRP), publications 60 and 103, respectively.

CONCLUSION

Our current (82)Rb dosimetry suggests reasonably low radiation exposure. On the basis of this study, a clinical (82)Rb injection of 2 × 1,480 MBq (80 mCi) would result in a mean effective dose of 3.7 mSv using the weighting factors of the ICRP 103-only slightly above the average annual natural background exposure in the United States (3.1 mSv).

Reference ranges for LVEF and LV volumes from electrocardiographically gated 82Rb cardiac PET/CT using commercially available software

Electrocardiographic gating is increasingly used for (82)Rb cardiac PET/CT, but reference ranges for global functional parameters are not well defined. We sought to establish reference values for left ventricular ejection fraction (LVEF), end systolic volume (ESV), and end diastolic volume (EDV) using 4 different commercial software packages. Additionally, we compared 2 different approaches for the definition of a healthy individual.

METHODS

Sixty-two subjects (mean age +/- SD, 49 +/- 9 y; 85% women; mean body mass index +/- SD, 34 +/- 10 kg/m(2)) who underwent (82)Rb-gated myocardial perfusion PET/CT were evaluated. All subjects had normal myocardial perfusion and no history of coronary artery disease (CAD) or cardiomyopathy. Subgroup 1 consisted of 34 individuals with low pretest probability of CAD (<10%), and subgroup 2 comprised 28 subjects who had no atherosclerosis on a coronary CT angiogram obtained concurrently during the PET/CT session. LVEF, ESV, and EDV were calculated at rest and during dipyridamole-induced stress, using CardIQ Physio (a dedicated PET software) and the 3 major SPECT software packages (Emory Cardiac Toolbox, Quantitative Gated SPECT, and 4DM-SPECT).

RESULTS

Mean LVEF was significantly different among all 4 software packages. LVEF was most comparable between CardIQ Physio (62% +/- 6% and 54% +/- 7% at stress and rest, respectively) and 4DM-SPECT (64% +/- 7% and 56% +/- 8%, respectively), whereas Emory Cardiac Toolbox yielded higher values (71% +/- 6% and 65% +/- 6%, respectively, P < 0.001) and Quantitated Gated SPECT lower values (56% +/- 8% and 50% +/- 8%, respectively, P < 0.001). Subgroup 1 (low likelihood) demonstrated higher LVEF values than did subgroup 2 (normal CT angiography findings), using all software packages (P < 0.05). However, mean ESV and EDV at stress and rest were comparable between both subgroups (p = NS). Intra- and interobserver agreement were excellent for all methods.

CONCLUSION

The reference range of LVEF and LV volumes from gated (82)Rb PET/CT varies significantly among available software programs and therefore cannot be used interchangeably. LVEF results were higher when healthy subjects were defined by a low pretest probability of CAD than by normal CT angiography results.

Depression Among Adults With Diabetes: Prevalence, Impact, and Treatment Options

In Brief

Patients with type 1 or type 2 diabetes are two times more likely to experience depression than their peers without diabetes. Comorbid depression results in deleterious effects on glycemic control, worsened diabetes complications, functional disability, and premature mortality. Once identified, depression can be effectively treated with antidepressant medications, psychotherapy, or a combination of both. Patients and providers should monitor depressive symptoms to identify their recurrence and work collaboratively to address barriers to care that exist in both urban and rural areas.

A Model of Community-Based Behavioral Intervention for Depression in Diabetes: Program ACTIVE

Depression affects one in four people with diabetes and significantly affects diabetes health. Earlier studies of the treatment of depression have documented that cognitive behavioral therapy (CBT) and exercise have each been found to be effective in treating depression in people with and without diabetes in the context of medical settings. Individuals in rural areas lack regular access to medical centers and require treatment options that may be adapted for local communities. To date, no studies have combined CBT and exercise for people with diabetes. This article presents a translational behavioral depression intervention study designed for individuals with type 2 diabetes in a rural Appalachian region as a model of an interdisciplinary approach to the treatment of depression in diabetes.

Complement receptor 2 polymorphisms associated with systemic lupus erythematosus modulate alternative splicing

Genetic factors influence susceptibility to systemic lupus erythematosus (SLE). A recent family-based analysis in Caucasian and Chinese populations provided evidence for association of single-nucleotide polymorphisms (SNPs) in the complement receptor 2 (CR2/CD21) gene with SLE. Here we confirmed this result in a case-control analysis of an independent European-derived population including 2084 patients with SLE and 2853 healthy controls. A haplotype formed by the minor alleles of three CR2 SNPs (rs1048971, rs17615, rs4308977) showed significant association with decreased risk of SLE (30.4% in cases vs 32.6% in controls, P=0.016, OR=0.90 (0.82-0.98)). Two of these SNPs are in exon 10, directly 5' of an alternatively spliced exon preferentially expressed in follicular dendritic cells (FDC), and the third is in the alternatively spliced exon. Effects of these SNPs and a fourth SNP in exon 11 (rs17616) on alternative splicing were evaluated. We found that the minor alleles of these SNPs decreased splicing efficiency of exon 11 both in vitro and ex vivo. These findings further implicate CR2 in the pathogenesis of SLE and suggest that CR2 variants alter the maintenance of tolerance and autoantibody production in the secondary lymphoid tissues where B cells and FDCs interact.

Integration of Infarct Size, Tissue Perfusion, and Metabolism by Hybrid Cardiac Positron Emission Tomography/Computed Tomography

Background— Hybrid positron emission tomography/computed tomography (PET-CT) allows for combination of PET perfusion/metabolism imaging with infarct detection by CT delayed contrast enhancement. We used this technique to obtain biomorphological insights into the interrelation between tissue damage, inflammation, and microvascular obstruction early after myocardial infarction.

Methods and Results— A porcine model of left anterior descending coronary artery occlusion/reperfusion was studied. Seven animals underwent PET-CT within 3 days of infarction, and a control group of 3 animals was scanned at >4 weeks. Perfusion and glucose uptake were assessed by [ 13 N]-ammonia/[ 18 F]-deoxyglucose (FDG), and 64-slice CT delayed contrast enhancement was measured. In the acute infarct model, CT revealed a no-reflow phenomenon suggesting microvascular obstruction in 80% of all infarct segments. PET showed increased FDG uptake in 68% of the CT-defined infarct segments. Ex vivo staining and histology showed active inflammation in the acute infarct area as an explanation for increased glucose uptake. In chronic infarction, CT showed no microvascular obstruction and agreed well with matched perfusion/metabolism defects on PET.

Conclusions— Perfusion/metabolism PET and delayed enhancement CT can be combined within a single hybrid PET-CT session. Increased regional FDG uptake in the acute infarct area is frequently observed. In contrast to the chronic infarct setting, this indicates tissue inflammation that is commonly associated with microvascular obstruction as identified by no reflow on CT. The consequences of these pathophysiological findings for subsequent ventricular remodeling should be explored in further studies.

Opioid detoxification using naloxone

A method of brief inpatient opioid detoxification using naloxone is described. Daily injections of naloxone were administered to 20 patients who were dependent on opioids until no physical withdrawal reaction occurred. A reducing regime of clonidine and diazepam was used to treat withdrawal symptoms. Seventy-five percent of patients successfully completed detoxification within 6 days. Withdrawal symptoms were minimal and rapidly declined during treatment. Unlike other techniques using opioid antagonists detoxification with daily naloxone injections requires minimal medical supervision, enables full participation in a daily relapse prevention programme and results in discharge from hospital without medication for symptomatic relief.

A polymorphism within interleukin-21 receptor (IL21R) confers risk for systemic lupus erythematosus and is associated with malar rash in lupus patients (49.17)

Interleukin (IL) 21 is a member of the type I cytokine superfamily that exerts a variety of effects on the immune system including B cell activation, plasma cell differentiation, and immunoglobulin production. The IL21 receptor (IL21R) is expressed on B cells, T cells, NK cells, and monocyte-derived dendritic cells. The expression of IL21R is reduced in B cells from lupus patients, while IL21 serum levels are increased in both lupus patients and some lupus-murine models. We recently reported that polymorphisms within the IL21 gene are associated with increased susceptibility to lupus. Herein, we genotyped SNPs in the IL21R gene located on chromosome 16p11. We identify and confirm the association between rs3093301 and lupus in two independent European-derived and Hispanic cohorts (p=7.2X10-5). In addition, the presence of the homozygous risk genotype in rs3093301 (A/A) was associated with the development of malar rash in the European-derived female lupus patients (OR=2.83, 95% CI=1.56-5.13, p=0.00045).

C8orf13/BLK association with systemic lupus erythematosus across different ethnicities (136.28)

SLE is a complex autoimmune disease with immunological abnormalities that targets B cell functions and development. Previous genome-wide association studies identified C8orf13/BLK as a novel SLE risk factor. BLK (B lymphoid tyrosine kinase) has been shown to have potential effects on B cell develoment. The main objectives of this study are to: 1.) assess this association in independent populations and 2.) determine if BLK risk alleles correlate with alteration in peripheral blood B cell development and protein expression. We genotyped 52 SNPs within the C8orf13/BLK region in European-derived, Asian and African American populations. rs13277113 is associated with SLE in all three populations. A few novel upstream SNPs within the intergenic region demonstrate a stronger association in Asians. Flow cytometry data suggests there is a significant difference in BLK expression and T2 cells B cell numbers between high-risk and non-risk individuals based on the risk haplotype. Our results suggest that the BLK genetic polymorphisms alter immune system development and function to increase the risk for SLE development. Supported by NIH RR020143, RR015577, NIAID-DAIT-BAA-05-11, AI031584, AR053483, AR48940, AI063274, AR052125, AR043247 and OCAST # HR08-037.

The effect of ractopamine supplementation at 5 ppm of swine finishing diets on growth performance, carcass composition and ultimate pork quality

Five hundred thirty-six finishing pigs were placed on experiment for an average of 26 d prior to slaughter, to determine the effects of 5 mg ractopamine hydrochloride (RAC) per kg of diet on growth performance, carcass composition and the eating quality of pork. Treatments included a control diet similar to a western Canadian commercial finishing diet and a treatment diet containing 5 mg RAC kg-1 with elevated amino acids, vitamins and minerals. The experiment started when average animal weight was 86 kg; pigs were marketed at an average liveweight of 118 kg. Two pigs were selected from each of 32 pens in week 4 of the experiment, for detailed carcass and meat quality evaluation, providing 16 pigs per gender per treatment. RAC-fed pigs reached market weight 4 d sooner (P < 0.05), grew 13 % faster (P < 0.05) and had 13% better feed efficiency (P < 0.05) than the controls. RAC-fed pigs also had 1 mm less backfat and 2.5 mm thicker loins (P < 0.05). Ultimate pH, purge loss and visual colour scores were unaffected by treatment but RAC-fed pigs had lower CIE a* and b* measurements (P < 0.05). RAC had no effect on juiciness, flavour, saltiness or overall acceptability (P > 0.10), but increased Warner-Bratzler shear force and reduced taste panel tenderness slightly (P < 0.05). The inclusion of 5 mg RAC kg-1 in a commercial finishing diet will increase the rate and efficiency of gain and improve carcass composition. Minimal impact on pork quality can also be expected with the use of RAC fed at this level. Key words: Ractopamine, swine, carcass composition, pork quality, beta-adrenergic agonist

Relationship of coronary calcium and myocardial perfusion in individuals with chest pain. Assessed by integrated rubidium-82 PET-CT

AIM

The integrated value of coronary calcium scoring added to myocardial perfusion assessment in hybrid PET-CT imaging remains poorly defined. In the present study, we sought to determine the relationship between calcium burden, other risk factors, and tissue perfusion in a group of patients with chest pain and predominantly intermediate likelihood for coronary artery disease.

PATIENTS, METHODS

In 70 patients, coronary calcium scores (CCS) were obtained in addition to rest/dipyridamole stress 82Rb perfusion images using a GE Discovery Rx hybrid PET-CT system. From static perfusion images, summed rest, stress and difference scores (SRS, SSS, SDS) were calculated using a 20-segment model. Absolute CCS was determined according to Agatston and age-, gender-, and ethnicity-matched CCS percentiles were calculated using the MESA database.

RESULTS

SSS, SRS and SDS were abnormal (>or=4) in 25 (36%), 17 (24%), and 12 (17%) patients. Mean CCS according to Agatston was 180+/-446(range 0-2122), and CCS percentile was 42+/-43(range 0-99). Absolute CCS correlated mildly but significantly with SSS (r=0.31, p=0.01), while CCS percentile did not (r=0.11, p=0.36). Of 49 patients with normal perfusion, 25 (57%) had CCS=0, and 8 (18%) had a CCS percentile>or=75th. Of 35 patients with a CCS=0, 26 (74%) had normal perfusion. Individuals in whom review of patient records revealed events during follow-up (n=10) had significantly higher SSS than those where no events were recorded (6.0+/-7.2 versus 2.9+/-3.1, p=0.03), and there was a trend towards higher CCS percentiles (62+/-36 versus 35+/-43, p=0.06).

CONCLUSION

Coronary calcifications and myocardial tissue perfusion, as interrogated in a single PET-CT imaging session, show only partial agreement in patients with chest pain. Both tests seem to reflect different pathophysiologic components, and may be complementary for definition of individual disease patterns.

Determinants of the response of left ventricular ejection fraction to vasodilator stress in electrocardiographically gated 82rubidium myocardial perfusion PET

PURPOSE

Myocardial perfusion imaging with (82)Rb PET allows for ECG-gated studies to be obtained early after radiotracer injection, capturing ventricular function close to peak pharmacologic action of dipyridamole. This is different from gated SPECT and may potentially provide additional diagnostic information. We sought to identify potential correlates of the PET-derived ejection fraction response to vasodilator stress.

METHODS

One hundred ten consecutive patients undergoing (82)Rb PET myocardial perfusion imaging during evaluation for coronary artery disease were included. Using a GE Discovery STRx PET-CT scanner, ECG-gated images (eight bins) were obtained at rest and 4 min after dipyridamole infusion, 90 s after infusion of 1,480-2,220 MBq of (82)Rb. Summed rest, stress, and difference scores (SRS, SSS, and SDS) were determined using a five-point scoring system and 20-segment model. Ejection fraction was calculated using automated QGS software.

RESULTS

Significant reversibility (SDS > or = 4) was found in 23 patients (21%). Mean LVEF in all patients was 47 +/- 13% at rest and 53 +/- 13% during dipyridamole. LVEF increased in 89 patients, and decreased in 17 patients during vasodilation. The change in LVEF was inversely correlated with SDS (r = -0.26; p = 0.007). Additionally, it was inversely correlated with resting LVEF (r = -0.20; p = 0.03) and SSS (r = -0.25; p = 0.009). No significant correlations were observed with SRS, heart rate, blood pressure, age, hypertension, hypercholesterolemia, or pretest likelihood of disease. At multivariate regression analysis, SDS was an independent predictor of the change in LVEF.

CONCLUSIONS

Gated (82)Rb PET during pharmacologic stress allows for assessment of the functional response to vasodilation. The magnitude of LVEF increase is determined by stress perfusion/reversible perfusion defects. Functional response to hyperemia may thus be incorporated in future evaluations of diagnostic and prognostic algorithms based on (82)Rb PET.