Pippa Storey

R2* imaging of transfusional iron burden at 3T and comparison with 1.5T

To determine normative R2* values in the liver and heart at 3T, and establish the relationship between R2* at 3T and 1.5T over a range of tissue iron concentrations.

Diffusion tensor imaging of subcortical brain injury in patients infected with human immunodeficiency virus

Diffusion tensor imaging (DTI) was used to derive in vivo tissue status measurements of subcortical brain regions that are vulnerable to injury in human immunodeficiency virus (HIV)-infected patients. Quantitative measurements, including the mean diffusivity (MD) and fractional anisotropy (FA), were determined in lateralized basal ganglia (caudate and putamen) and centrum semiovale in 11 well-characterized HIV patients and in 11 control subjects. DTI measurements were examined for patterns of relationship with markers of clinical and cognitive progression. DTI measures acquired in subcortical regions were significantly correlated with loss of function in specific cognitive domains. Significant relationships were identified between measures for putamen and verbal memory (MD), visual memory (FA), working memory (FA), and overall cognitive impairment (MD). Measures for caudate (FA) were significantly correlated with visual memory. Measures for centrum semiovale were significantly correlated with visual memory deficits (MD) and visuoconstruction (FA). Relationships between anisotropy measures and anemia (basal ganglia) and CD4 counts (centrum semiovale) were also observed. Findings from this investigation indicate that DTI is a sensitive tool for correlating neuroanatomic pathologic features with specific cognitive deficits in patients with HIV infection.

Evaluation of the Reproducibility of Intrarenal and Measurements Following Administration of Furosemide and During Waterload

To estimate the reproducibility of BOLD MRI measurements in the evaluation of intrarenal oxygenation levels.

Band Artifacts Due to Bulk Motion

Band artifacts due to bulk motion were investigated in images acquired with fast gradient echo sequences. A simple analytical calculation shows that the width of the artifacts has a square‐root dependence on the velocity of the imaged object, the time taken to acquire each line of k‐space and the field of view in the phase‐encoding direction. The theory furthermore predicts that the artifact width can be reduced using parallel imaging by a factor equal to the square root of the acceleration parameter. The analysis and results are presented for motion in the phase‐ and frequency‐encoding directions and comparisons are made between sequential and centric ordering. The theory is validated in phantom experiments, in which bulk motion is simulated in a controlled and reproducible manner by rocking the scan table back and forth along the bore axis. Preliminary cardiac studies in healthy human volunteers show that dark bands may be observed in the endocardium in images acquired with nonsegmented fast gradient echo sequences. The fact that the position of the bands changes with the phase‐encoding direction suggests that they may be artifacts due to motion of the heart walls during the image acquisition period. Magn Reson Med 48:1028–1036, 2002.

Serial Diffusion Tensor Imaging Detects White Matter Changes That Correlate with Motor Outcome in Premature Infants

The objective of the study was to assess predictive value of serial diffusion tensor MRI (DTI) for the white matter injury and neurodevelopmental outcome in a cohort of premature infants. Twenty-four infants less than 32 weeks’ gestation were stratified to a control group (n = 11), mild brain injury with grades 1–2 of intraventricular hemorrhage (n = 6) and severe brain injury with grades 3–4 intraventricular hemorrhage (n = 4). Serial DTI studies were performed at around 30 and 36 weeks’ gestation. Fractional anisotropy (FA) and apparent diffusion coefficient were calculated. Twelve infants were followed up for developmental outcome. Developmental testing was performed with the Bayley Scales of Infant Development to obtain psychomotor index (Performance Developmental Index). Apparent diffusion coefficient was higher in the severe injury group at the second MRI in the central and occipital white matter, and corona radiata; FA was lower in optic radiation compared to controls. Performance Developmental Indexscore correlated with FA on the scan taken at the 30th week and inversely with the change of FA between scans in internal capsule and occipital white matter. A low value of FA at 30 weeks and a higher change of FA predicted less favorable motor outcome at 2 years and suggests that early subtle white matter injury can be detected in premature infants even without obvious signs of injury.

MR ventilation‐perfusion imaging of human lung using oxygen‐enhanced and arterial spin labeling techniques

Magnetic resonance ventilation‐perfusion (V/Q) imaging has been demonstrated using oxygen and arterial spin labeling techniques. Inhaled oxygen is used as a paramagnetic contrast agent in ventilation imaging using a multiple inversion recovery (MIR) approach. Pulmonary perfusion imaging is conducted using a flow‐sensitive alternating inversion recovery with an extra radiofrequency pulse (FAIRER) technique. A half Fourier single‐short turbo spin echo (HASTE) sequence is used for data acquisition in both techniques. V/Q imaging was performed in ten of the twenty volunteers, while either ventilation or perfusion was imaged in the other ten. This V/Q imaging scheme is completely noninvasive, does not involve ionized radiation, and shows promising potential for clinical use in the diagnosis of lung diseases such as pulmonary embolism. J. Magn. Reson. Imaging 2001;14:574–579.

Impact of lung volume on MR signal intensity changes of the lung parenchyma

To test the hypothesis that, in magnetic resonance (MR) imaging of healthy individuals, equal relative changes in lung volume cause equal relative changes in MR signal intensity of the lung parenchyma.

Kidneys in hypertensive rats show reduced response to nitric oxide synthase inhibition as evaluated by BOLD MRI.

To examine whether the noninvasive technique of blood oxygenation level dependent magnetic resonance imaging (BOLD MRI) can detect changes in renal medullary oxygenation following administration of a nitric oxide (NO) synthase inhibitor, NG‐nitro‐L‐arginine methyl ester (L‐NAME). Hypertension is associated with endothelial dysfunction and is characterized by a lack of response to endothelial‐dependent vasoactive substances, including nitric oxide synthase inhibitors. We hypothesized that the magnitude of the change would be reduced in the kidneys of hypertensive subjects relative to normal controls.

Disease burden in HIV-associated cognitive impairment: A study of whole-brain imaging measures

Objective: To study whole-brain MR measures derived from diffusion tensor imaging and magnetization transfer imaging (MTI) for the in vivo assessment of cumulative neuropathologic changes in HIV and to evaluate the quantitative imaging strategies with respect to cognitive status measures including the severity of dementia and the degree of impairment in specific cognitive domains including attention, memory, constructional abilities, and motor speed. Methods: Quantitative whole-brain measurements, including fractional anisotropy (FA), apparent diffusion coefficient (ADC), and magnetization transfer ratio (MTR), were derived from histograms and compared in HIV and control participants. Relationships between the MR and cognitive status measures were examined. Results: Whole-brain FA and MTR were reduced in patients with HIV and correlated with dementia severity. Whole-brain MTR and ADC were correlated with psychomotor deficits. Evaluation of relationships between the studied MR measures indicated a correlation between ADC and MTR; FA was not correlated with either ADC or MTR. Conclusions: Findings from this investigation support the use of quantitative whole-brain MR measures for evaluation of disease burden in HIV. Reductions in whole-brain fractional anisotropy and magnetization transfer ratio (MTR) distinguished HIV and control subjects, and these measures were associated with dementia severity. Relationships were identified between whole-brain MTR and apparent diffusion coefficient and psychomotor deficits. Combining these quantitative strategies in neuroimaging examinations may provide more comprehensive information concerning ongoing changes in the brains of HIV patients.

Flow artifacts in steady‐state free precession cine imaging

Steady‐state free precession (SSFP) cardiac cine images are frequently corrupted by dark flow artifacts, which can usually be eliminated by reshimming and retuning the scanner. A theoretical explanation for these artifacts is provided in terms of spins moving through an off‐resonant point in the magnetic field, and the theory is validated using phantom experiments. The artifacts can be reproduced in vivo by detuning the center frequency by an amount in the range of half the inverse repetition time (TR). Since this offset is similar in magnitude to the frequency difference between the water and lipid peaks, a likely cause of the artifacts in vivo is that the center frequency is tuned incorrectly to the lipid peak rather than the water peak. Magn Reson Med 51:115–122, 2004.