Half-dose Protocol Research Articles

3D PET/CT 82Rb PET myocardial blood flow quantification: comparison of half-dose and full-dose protocols.

Quantification of myocardial blood flow (MBF) has become central in the clinical application of Rubidium-82 (82Rb) PET myocardial perfusion scans. Current recommendations suggest injections of 1100-1500MBq of 82Rb in bolus form, which poses a potential risk of PET system saturation on most 3D PET/CT systems currently being used. We aimed to evaluate the frequency and impact of PET system saturation and to test the potential use of a half-dose acquisition protocol. This study comprised 20 patients who underwent repeated rest scans in a single imaging session, one employing a full-dose (FD), and the other scan a half-dose (HfD) protocol. Datasets were evaluated for saturation based on visual assessments of input functions and sinograms. We compared FD and HfD MBF measurements using Bland-Altman plots, coefficients of variation (CV), and paired t tests. A correction factor permitting serial analyses using FD/HfD imaging protocols was obtained using only the datasets without saturation. A dose reduction of 47% was reported for the HfD protocol (FD, 1247 ± 196MBq; HfD, 662 ± 115MBq). Saturation effects were observed in 4/20 (20%) FD scans, with none observed in the 20 HfD scans. Assessment of MBFs for FD and HfD protocols revealed bias in the MBF assessments of 0.09ml/g/min (global MBF, FD = 1.03 ± 0.29 vs HfD = 0.94 ± 0.22ml/g/min (p = 0.001)). Exclusion of patients with visually identified saturation effects (N = 4) reduced the bias to 0.05ml/g/min (global MBF, FD = 0.97 ± 0.28 vs HfD = 0.92 ± 0.23ml/g/min (p = 0.02)). From the datasets without saturation effect, it was possible to generate a bias-correction: Corrected MBFHfD = 1.09*MBFHfD-0.03ml/g/min. MBFFD and MBFHfD did not differ following the bias correction (MBFFD = 0.97 ± 0.28, MBFHfD,corrected = 0.98 ± 0.25ml/g/min, p = 0.77). Saturation effects can be problematic in 82Rb MBF studies using the recommended FD protocols for 3D PET/CT scanners. The use of HfD protocol eliminates the risks of saturation and should be used instead of clinical protocols to avoid erroneous results.

Half-dose Coronary Artery Calcium Scoring: Impact of Iterative Reconstruction.

The purpose of this study was to assess the impact of adaptive statistical iterative reconstruction (ASiR) on half-dose coronary artery calcium scoring (CACS) acquisition protocol. Between September 2016 and October 2017, 89 patients (54 male patients, mean age 64.6±10.7 y) with a clinically indicated coronary computed tomography angiography were prospectively enrolled. On a 64-row computed tomography scanner, patients underwent a standard CACS protocol (120 kVp, 170 mAs) reconstructed by filtered-back projection, and a half-dose CACS protocol (120 kVp, 85 mAs) reconstructed by ASiR at different percentages, from 10% to 100%, in 10% increments. CACS determinants (Agatston score, number of plaques, volume, and mass), signal-to-noise ratio, contrast-to-noise ratio, and radiation dose of both protocols were calculated. Patient risk categories based on CACS were determined for each protocol, and analysis of risk reclassification of half-dose protocol was performed. Depending on their body mass index (BMI), patients were divided into nonobese (BMI<30 kg/m) and obese (BMI≥30 kg/m) groups to investigate the influence of BMI on CACS determinants and risk reclassification. Half-dose protocol reconstructed with ASiR 70% showed no significant differences in any CACS determinant compared with the standard protocol for both nonobese and obese patients (all P≥0.070 and ≥0.066, respectively) and reclassified 1 (1.7%) and 6 (20.0%) patients, respectively, with excellent (κ=0.91) and good (κ=0.74) agreement with standard protocol, respectively. ASiR 70% also resulted in a higher signal-to-noise ratio (1.88±0.78) and contrast-to-noise ratio (7.10±2.73) compared with standard protocol (all P≤0.001). Half-dose protocol provided 52% less radiation dose than standard acquisition (0.31±0.06 vs. 0.64±0.10 mSv; P<0.001). ASIR 70% coupled with reduction of tube current by 50% allowed for significant dose reduction and no detrimental effects on image quality, with minimal patient reclassification in nonobese patients. In obese patients, excessive noise may lead to a clinically significant reclassification rate.

Comparison of conventional L-thyroxine withdrawal and moderate hypothyroidism in preparation for whole-body 131-I scan and thyroglobulin testing.

After thyroidectomy for thyroid cancer, patients often withdraw L-T4 for diagnostic or therapeutic purposes, showing signs and symptoms of hypothyroidism. A slighter hypothyroidism (reducing L-T4 to one-half) has been proposed to limit these inconveniences. We evaluated half-dose L-T4 protocol, in comparison to conventional L-T4 withdrawal, in terms of effectiveness and improvement of clinical and biochemical disorders. We randomized 55 thyroid cancer patients into two groups: 29 patients underwent 5 weeks of half-dose of previous L-T4 treatment (HD group); 26 patients replaced L-T4 with L-T3 for 3 weeks followed by 2 weeks of withdrawal (TW group). Clinical features (Zulewsky clinical score) and biochemical parameters (lipids, liver, and muscle enzymes) were evaluated in all patients at baseline and after 5 weeks. Total cholesterol, creatine kinase, lactate dehydrogenase, aspartate aminotransferase, and alanine aminotransferase increased at 5 weeks in both groups, but significantly more in TW, but no difference was found by clinical score. Patients who achieved the thyroid-stimulating hormone (TSH) target value (25 µU/ml) were 92.3% in TW group and 48.3% in HD group (p < 0.001). In the HD group, only basal TSH statistically correlated with the achievement of the TSH target. Receiver operating characteristic curves indicated that a basal TSH ≥0.52 μU/ml is required to reach an adequate TSH level. Half-dose L-T4 protocol, compared to conventional L-T4 withdrawal, is associated with less biochemical disorders but no significant clinical advantage. Therefore, the half-dose protocol reaches an adequate TSH target in 48.3% of patients and is not effective unless basal serum TSH is ≥0.52 μU/ml.

Whole-body CT for lymphoma staging: Feasibility of halving radiation dose and risk by iterative image reconstruction

ObjectivesPatients with lymphoma are at higher-risk of secondary malignancies mainly due to effects of cancer therapy as well as frequent radiological surveillance. We thus aimed to investigate the objective and subjective image quality as well as radiation exposure and risk of full-dose standard (FDS), full-dose iterative (FDI), and half-dose iterative (HDI) image reconstruction in patients with lymphoma. Material and methodsIn 100 lymphoma patients, contrast-enhanced whole-body staging was performed on a dual-source CT. To acquire full-dose and half-dose CT data simultaneously, the total current-time product was equally distributed on both tubes operating at 120kV. HDI reconstructions were calculated by using only data from one tube. Quantitative image quality was assessed by measuring image noise in different tissues of the neck, thorax, and abdomen. Overall diagnostic image quality was assessed using a 5-point Likert scale. Radiation doses and risks were estimated for a male and female reference person. ResultsFor all anatomical regions apart from the lungs image noise was significantly lower and the overall subjective image quality significantly better when using FDI and HDI instead of FDS reconstruction (p<0.05). For the half-dose protocol, the risk to develop a radiation-induced cancer was estimated to be less than 0.11/0.19% for an adult male/female. ConclusionsImage quality of FDI and more importantly of HDI is superior to FDS reconstruction, thus enabling to halve radiation dose and risk to lymphoma patients.

Raw-data-based iterative reconstruction versus filtered back projection: image quality of low-dose chest computed tomography examinations in 87 patients

ObjectiveThe objective was to compare standard-dose chest computed tomography (CT) reconstructed with filtered back projection (FBP) versus low-dose images with FBP and raw-data-based iterative reconstruction. MethodsEighty-seven consecutive patients (46 male; mean age, 54.54±16.12; mean body mass index, 24.58±4.07) referred for initial chest CT with full-dose examinations [mean dose–length product (DLP), 183.37±44.13 mGy·cm] and follow-up chest CT with half-dose examinations (mean DLP, 91.08±23.81 mGy·cm) were included. The full-dose protocol was reconstructed with FBP; the half-dose protocol was reconstructed with FBP and sinogram-affirmed iterative reconstruction (SAFIRE). Noise and signal-to-noise ratio were compared using a paired Student’s t test; subjective image quality and lesion conspicuity were compared using Wilcoxon signed ranks test. ResultsActual radiation dose of follow-up CT was about 50% (49.26%±2.62%) of standard-dose protocol. Compared to full-dose images with FBP, there was no significant difference in half-dose images with SAFIRE in the objective noise (ascending aorta: P=.38, descending aorta: P=.70, trachea on mediastinal images: P=.37) and SNR (ascending aorta: P=.14, descending aorta: P=.72, trachea on mediastinal images: P=.06) on mediastinal images. Noise was significantly lower (P<.001) and SNR was significantly higher (P<.001) in half-dose images with SAFIRE on lung images. Noise was significantly higher (P<.001) and SNR was significantly lower (P<.001) in half-dose images with FBP. Subjective image quality was similar on both mediastinal images (P=.317) and lung images (P=.614) of half-dose SAFIRE images versus full-dose FBP images. Lesion conspicuity was also similar. Subjective image quality was significantly lower on both mediastinal images (P<.001) and lung images (P<.001) of half-dose FBP images versus full-dose FBP images. The conspicuity of some lesions was significantly lower (ground-glass opacity, P<.0001; ill-defined micronodule, P<.0001; lung cyst, P<.0001; emphysematous lesion, P=.003) on half-dose FBP versus full-dose FBP images. ConclusionCompared to full-dose CT images reconstructed with the conventional FBP algorithm, SAFIRE with three iterations could provide similar or better image quality at 50% less dose.

Shortened acquisition time or reduced-activity dose for gated myocardial perfusion SPECT with new reconstruction algorithm

To confirm that shortened acquisition time or reduced-activity dose in single-photon emission computed tomography (SPECT) myocardial perfusion imaging reconstructed with Astonish software (AS) does not compromise image quality or diagnostic accuracy. One hundred patients referred for SPECT myocardial perfusion imaging were prospectively studied. The patients were randomly selected to receive the full-dose protocol (group A, n = 54) or the half-dose protocol (group B, n = 46). The patients of group A underwent a 2-day stress/rest protocol. After half-time acquisition, they underwent a full-time acquisition for stress and rest SPECT. Group B underwent a 1-day stress/rest protocol. During peak stress, all patients received an intravenous injection of (99m)Tc-methoxyisobutylisonitrile (MIBI; 5.2 ± 0.6 mCi). After the full-time stress acquisition, the patients underwent a double-time stress acquisition. If the stress image showed a defect, a patient received (99m)Tc-MIBI (19.5 ± 1.7 mCi) at rest on the same day. The rest SPECT acquisition protocol was the same in both groups. The low count (LC) and high count (HC) were acquired for each patient. AS and filtered back projection (FBP) reconstructed each set of raw data. Image quality of perfusion was assessed on a four-point scale. Perfusion parameters and function parameters were calculated by quantitative perfusion SPECT and quantitative gated SPECT. Mean image quality for LC-AS and HC-AS (3.5 ± 0.5 and 3.7 ± 0.5, respectively) was superior to HC-FBP (3.1 ± 0.4) in group A (for all, p < 0.001). LC-AS and HC-AS (3.5 ± 0.5 and 3.6 ± 0.5, respectively) in group B were superior to HC-FBP (3.1 ± 0.3) (for all, p < 0.001). LC-AS, HC-AS and LC-FBP showed high diagnostic concordance with HC-FBP (kappa value was 0.92, 0.92, and 0.94, respectively; all p < 0.001). Cardiac SPECT studies can be acquired with half of the scan time or reduced radioactivity dose and reconstructed by using the AS algorithm without compromising image quality.

Étude prospective randomisée protocoles agonistes long versus court chez les patientes mauvaises répondeuses en fécondation in vitro

ObjectivesDifferent ovarian stimulation protocols are used for in vitro fertilization (IVF) in “poor responder” patients. Our work aims at comparing two ovarian stimulation protocols (long agonist half-dose protocol versus short agonist protocol without pretreatment) in this population of women. Patients and methodsThis prospective, randomized study was realized at the University Hospital of Saint-Étienne and concerns “poor responder” patients (age between 38 and 42years and FSH at day 3 more than 9.5IU/L; and/or antral follicles count less or equal to 6; and/or failure of previous stimulation). The primary endpoint is based on the number of oocytes retrieved at the end of an IVF cycle. ResultsOut of the 44 patients randomized, 39 cycles were taken into account (20 in the long protocol, 19 in the short one). At the end of the stimulation (FSH-r 300 to 450UI/d), the number of follicles recruited appears higher in the long protocol but the difference is not significant (diameter between 14 and 18mm: 3.0±2.31 vs 1.88±1.89 and diameter greater than 18mm: 3.9±2 85 vs 3.06±2.77). The same tendency is observed for all the following criteria: the number of retrieved oocytes (6.74±2.73 vs 6.38±4.26), the total number of embryos (3.16±2.03 vs 2.25±2.11), the pregnancy rate per retrieval (21% vs 19%) and per cycle (20% vs 16%), and the number of children born alive. Discussion and conclusionThe study did not reveal any difference between the two protocols but the long half-dose seems to be better.