Structural MRI and calibrated fMRI during a cognitive Stroop task in the normal aged human brain

Background: In recent years, structural magnetic resonance imaging (MRI) studies have shown dramatic age-associated changes in grey matter volume, density and cortical thickness. Calibrated functional magnetic resonance (fMRI) has become a recognized technique for quantifying both the cerebral blood flow (CBF) and oxygen metabolism (CMR02) changes associated with neural activation. It has been used as an advanced approach for examining the physiological effects of age-related changes in the brain, which may be difficult to interpret if measured by the blood oxygen level dependent (BOLD) signal alone. fMRI studies of aging have revealed increased BOLD response to tasks of executive' function with advancing age, which is generally interpreted as increased neural activity. However, changes in the cerebrovascular system with age can alter the BOLD/signal, complicating this interpretation. Arterial spin labeling (ASL) allows simultaneous acquisition of BOLD and CBF information and can be used to quantify the component parts of the BOLD signal. Aims: Hyperoxia calibration was applied during fMRI to study neurovascular alterations and correlations with age. We aimed: (1) address if age-related differences in the BOLD signal develop from age-related neural plasticity or age-related cerebrovascular changes during a cognitive Stroop task. (2) Understand the underlying physiology of the BOLD signal change that is seen with aging. (3) Determine regional variation in physiological changes with age. (4) Determine regional changes in grey matter density and cortical thickness with increasing age. (5) Assess the impact of this structural change on physiological change. Methods: We used calibrated fMRI approach in 55 healthy participants over an age range of 18-71 years to determine the relative vascular and neuronal contributions to the age-related BOLD changes in response to a Stroop task. We analysed the structural data with the new VBM-DARTEL technique. The cortical thicknesses were analysed using the FreeSurfer tools. Results: The BOLD response increased significantly with increasing age but the CBF response did not alter, such that the BOLD increase is attributed to a significant reduction in CMRO2 response with increasing age. Hence, in this study, the BOLD increase with age should be interpreted as a reduction in neural activity, which would be consistent with neurodegeneration. The greatest BOLD increases with age were found in left and right medial frontal gyri and primary motor cortex and were again linked to a reduction in CMRO2• Age-related decline in grey matter density and cortical thickness were widespread, but the frontal regions, in general, exhibit greater thickness changes than parietal, temporal and occipital. The strongest correlations between age and (BOLD activations, grey matter density, cortical thickness) were found mainly in the frontal cortices. The cortical structure-function relationships are different for each sex. Finally, better performance had been observed to be associated with larger frontal grey matter density and thicker cortex on some executive tasks, and increased frontal CMRO2 response. Conclusions: This study demonstrates the relationship between structure, function, and cognition, as well as the need to take into account alterations in vascular-metabolic coupling and resting blood volume when interpreting changes in the BOLD response with aging. It also highlights the added benefit that calibrated fMRI offers in terms of interpreting the underlying physiological changes that give rise to the measured BOLD response.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Calibrated fMRI during a cognitive Stroop task reveals reduced metabolic response with increasing age

fMRI studies of aging have revealed increased blood oxygenation level dependent (BOLD) response to tasks of executive function with advancing age, which is generally interpreted as increased neural activity. However, changes in the cerebrovascular system with age can alter the BOLD signal, complicating this interpretation. Arterial spin labeling (ASL) allows simultaneous acquisition of BOLD and cerebral blood flow (CBF) information and can be used to quantify the component parts of the BOLD signal. We used this calibrated BOLD approach in 58 healthy participants over an age range of 18-71. years to determine the relative vascular and neuronal contributions to the age-related BOLD changes in response to a Stroop task. The percentage BOLD response increased significantly with increasing age but the percentage CBF response did not alter, such that the BOLD increase is attributed to a significant reduction in the oxygen metabolism response with increasing age. Hence, in this study, the BOLD increase with age should be interpreted as a reduction in neural activity. The greatest percentage BOLD increases with age were found in the left and right medial frontal gyri and the primary motor cortex and were again linked to a reduction in oxygen metabolism. On separating the participants into three groups (young, old high performers and old low performers), age-related differences in percentage BOLD response and oxygen metabolism response could be attributed to the low performing old group. This study demonstrates the need to take into account alterations in vascular-metabolic coupling and resting blood volume when interpreting changes in the BOLD response with aging

Abdomen and pelvis computed tomography procedure: Effective dose assessment and establishment of a local diagnostic reference level

Exposure to ionizing radiation may induce cancer risk to the patients proportional to the radiation absorbed dose and the organ sensitivity. Therefore protection of radiation exposure is essential to minimize the radiation cancer risk and prevent the deterministic effects. The International Atomic Energy Agency (IAEA) encourages member countries to establish national diagnostic reference levels (DRLs) to reduce unjustified radiation exposure. This study establishes a local DRL for computed tomography (CT) abdomen and pelvis procedures. In total, 1444 CT abdomen procedures were carried out during nine months. CT abdomen procedures were carried out at King Faisal Specialist Hospital and research center using six CT machines from different vendors. The mean and range of patients’ weight (kg) are 50 (42–120). The recommended DRLs values in DLP (mGy.cm) and CTDIvol (mGy)were 900 and 15 per CT abdomen and pelvis procedure, respectively. 3% (41 cases) were higher than the national DRL for CT abdomen and pelvis. The proposed DRL values are slightly higher than the European and the American College of Radiologists (ACR) DRL values in DLP. The purpose of DRL in terms of CTDIvol (mGy) is comparable with the international guidelines. Thus reducing the scan length, is recommended ensuring that patients receive a minimal possible radiation dose while maintaining the image quality

Radiation Dose Optimization Based on Saudi National Diagnostic Reference Levels and Effective Dose Calculation for Computed Tomography Imaging: A Unicentral Cohort Study

Few studies have reviewed the reduction of doses in Computed tomography (CT), while various diagnostic procedures use ionizing radiation to explore the optimal dose estimate using multiple exposure quantities, including milliampere-seconds, kilovoltage peak, and pitch factors while controlling the CT dose index volume (CTDIvol) and dose length product (DLP). Therefore, we considered optimizing CT protocols to reduce radiation and organ doses during head, chest, abdominal, and pelvic CT examinations. For establishing institutional diagnostic reference levels as a benchmark to correlate with national diagnostic reference levels (NDRLs) in KSA conforming to international guidelines for radiation exposure, 3000 adult-patients underwent imaging of organs. Dose parameters were obtained using Monte Carlo software and adjusted using the Siemens Teamplay™ software. CTDIvol, DLP, and effective dose were 40.67 ± 3.8, 757 ± 63.2, and 1.74 ± 0.19, for head; 14.9 ± 1.38, 547 ± 42.9, and 7.27 ± 0.95 for chest; and 16.84 ± 1.45, 658 ± 53.4, and 10.2 ± 0.66 for abdomen/pelvis, respectively. The NDRL post-optimization comparison showed adequate CT exposure. Head CT parameters required additional optimization to match the NDRL. Therefore, calculations were repeated to assess radiation doses. In conclusion, doses could be substantially minimized by selecting parameters per clinical indication of the study, patient size, and examined body region. Additional dose reduction to superficial organs requires a shielding material

Radiation Dose Optimization Based on Saudi National Diagnostic Reference Levels and Effective Dose Calculation for Computed Tomography Imaging: A Unicentral Cohort Study

Few studies have reviewed the reduction of doses in Computed tomography (CT), while various diagnostic procedures use ionizing radiation to explore the optimal dose estimate using multiple exposure quantities, including milliampere-seconds, kilovoltage peak, and pitch factors while controlling the CT dose index volume (CTDIvol) and dose length product (DLP). Therefore, we considered optimizing CT protocols to reduce radiation and organ doses during head, chest, abdominal, and pelvic CT examinations. For establishing institutional diagnostic reference levels as a benchmark to correlate with national diagnostic reference levels (NDRLs) in KSA conforming to international guidelines for radiation exposure, 3000 adult-patients underwent imaging of organs. Dose parameters were obtained using Monte Carlo software and adjusted using the Siemens Teamplay™ software. CTDIvol, DLP, and effective dose were 40.67 ± 3.8, 757 ± 63.2, and 1.74 ± 0.19, for head; 14.9 ± 1.38, 547 ± 42.9, and 7.27 ± 0.95 for chest; and 16.84 ± 1.45, 658 ± 53.4, and 10.2 ± 0.66 for abdomen/pelvis, respectively. The NDRL post-optimization comparison showed adequate CT exposure. Head CT parameters required additional optimization to match the NDRL. Therefore, calculations were repeated to assess radiation doses. In conclusion, doses could be substantially minimized by selecting parameters per clinical indication of the study, patient size, and examined body region. Additional dose reduction to superficial organs requires a shielding material