Non-Contrast-Enhanced Carotid MRA: Clinical Evaluation of a Novel Ungated Radial Quiescent-Interval Slice-Selective MRA at 1.5T.

BACKGROUND AND PURPOSE: Non-contrast-enhanced MRA techniques have experienced a renaissance due to the known correlation between the use of gadolinium-based contrast agents and the development of nephrogenic systemic fibrosis and the deposition of gadolinium in some brain regions. The purpose of this study was to assess the diagnostic performance of ungated non-contrast-enhanced radial quiescent-interval slice-selective MRA of the extracranial supra-aortic arteries in comparison with conventional contrast-enhanced MRA in patients with clinical suspicion of carotid stenosis. MATERIALS AND METHODS: In this prospective study, both MRA pulse sequences were performed in 31 consecutive patients (median age, 68.8 years; 19 men). For the evaluation, the cervical arterial system was divided into 35 segments (right and left side). Three blinded reviewers separately evaluated these segments. An ordinal scoring system was used to assess the image quality of arterial segments and the stenosis grading of carotid arteries. RESULTS: Overall venous contamination in quiescent-interval slice-selective MRA was rated as "none" by all readers in 84.9% of cases and in 8.1% of cases in contrast-enhanced MRA (P < .0001). The visualization quality of arterial segments was considered good to excellent in 40.2% for the quiescent-interval slice-selective MRA and in 52.2% for the contrast-enhanced MRA (P < .0001). The diagnostic accuracy of ungated quiescent-interval slice-selective MRA concerning the stenosis grading showed a total sensitivity and specificity of 85.7% and 90.0%, respectively. CONCLUSIONS: Ungated quiescent-interval slice-selective MRA can be used clinically as an alternative to contrast-enhanced MRA without a significantly different image quality or diagnostic accuracy for the detection of carotid stenosis at 1.5T.

Advances in non-contrast quiescent-interval slice-selective (QISS) magnetic resonance angiography.

There is a pressing clinical need to develop accurate, efficient non-contrast magnetic resonance angiography (NC-MRA) techniques. Our efforts in the field have focused on a novel non-subtractive technique called quiescent-interval slice-selective (QISS) MRA. Compared with other NC-MRA techniques, QISS has the advantage of being more accurate while enabling a simpler and more efficient workflow. The original implementation, which uses electrocardiogram (ECG) gating and a Cartesian k-space trajectory, is a reliable technique for the evaluation of peripheral arterial disease (PAD). Recent advances in QISS technology include the use of a radial k-space trajectory, which facilitates rapid imaging of the coronary, renal, and pulmonary arteries as well as other vascular beds, and ungated ("UnQISS") acquisitions for PAD.

Quantitative Susceptibility Mapping in Cerebral Cavernous Malformations: Clinical Correlations.

BACKGROUND AND PURPOSE: Quantitative susceptibility mapping has been shown to assess iron content in cerebral cavernous malformations. In this study, our aim was to correlate lesional iron deposition assessed by quantitative susceptibility mapping with clinical and disease features in patients with cerebral cavernous malformations. MATERIALS AND METHODS: Patients underwent routine clinical scans in addition to quantitative susceptibility mapping on 3T systems. Data from 105 patients met the inclusion criteria. Cerebral cavernous malformation lesions identified on susceptibility maps were cross-verified by T2-weighted images and differentiated on the basis of prior overt hemorrhage. Mean susceptibility per cerebral cavernous malformation lesion (χ̄lesion) was measured to correlate with lesion volume, age at scanning, and hemorrhagic history. Temporal rates of change in χ̄lesion were evaluated in 33 patients. RESULTS: Average χ̄lesion per patient was positively correlated with patient age at scanning (P < .05, 4.1% change with each decade of life). Cerebral cavernous malformation lesions with prior overt hemorrhages exhibited higher χ̄lesion than those without (P < .05). Changes in χ̄lesion during 3- to 15-month follow-up were small in patients without new hemorrhage between the 2 scans (bias = -0.0003; 95% CI, -0.06-0.06). CONCLUSIONS: The study revealed a positive correlation between mean quantitative susceptibility mapping signal and patient age in cerebral cavernous malformation lesions, higher mean quantitative susceptibility mapping signal in hemorrhagic lesions, and minimum longitudinal quantitative susceptibility mapping signal change in clinically stable lesions. Quantitative susceptibility mapping has the potential to be a novel imaging biomarker supplementing conventional imaging in cerebral cavernous malformations. The clinical significance of such measures merits further study.

Quiescent-inflow single-shot magnetic resonance angiography using a highly undersampled radial k-space trajectory.

PURPOSE: We hypothesized that high undersampling factors could be used in conjunction with radial quiescent-inflow single-shot magnetic resonance angiography (MRA) to accelerate the data acquisition and enable multislice acquisitions. METHODS: Seven subjects were imaged on a 1.5 T MRI system. For multislice quiescent-inflow single-shot MRA, the venous saturation radiofrequency pulse, in-plane saturation radiofrequency pulse, and quiescent interval were applied only once before the first slice. RESULTS: The mean (standard deviation) measurements for the intra-arterial signal-to-noise ratio were as follows: Cartesian 1 slice-29.3 (5.5); radial 1 slice, 92 views-22.3 (3.6); radial 1 slice, 46 views-18.5 (2.0); radial 2 slices, 46 views-18.3 (3.2); and radial 3 slices, 32 views-21.7 (3.9), normalized for pixel size to 15.8. Horizontal striping was present with multislice radial quiescent-inflow single-shot MRA (especially with the three-slice acquisition) due to variable T1 relaxation between the concurrently acquired slices, but the image quality remained diagnostic. Vascular pathology in patients with peripheral arterial disease was well shown by all techniques. CONCLUSION: Very high undersampling factors in excess of 18 have been demonstrated for nonenhanced MRA using a radial quiescent-inflow single-shot technique, enabling the acquisition of two to three slices per cardiac cycle. Scan time for a complete peripheral MRA could be shortened to 2 min or less.

Evidence-based guideline: The role of diffusion and perfusion MRI for the diagnosis of acute ischemic stroke: report of the Therapeutics and Technology Assessment Subcommittee of the American Academy of Neurology.

OBJECTIVE: To assess the evidence for the use of diffusion-weighted imaging (DWI) and perfusion-weighted imaging (PWI) in the diagnosis of patients with acute ischemic stroke. METHODS: We systematically analyzed the literature from 1966 to January 2008 to address the diagnostic and prognostic value of DWI and PWI. RESULTS AND RECOMMENDATIONS: DWI is established as useful and should be considered more useful than noncontrast CT for the diagnosis of acute ischemic stroke within 12 hours of symptom onset. DWI should be performed for the most accurate diagnosis of acute ischemic stroke (Level A); however, the sensitivity of DWI for the diagnosis of ischemic stroke in a general sample of patients with possible acute stroke is not perfect. The diagnostic accuracy of DWI in evaluating cerebral hemorrhage is outside the scope of this guideline. On the basis of Class II and III evidence, baseline DWI volumes probably predict baseline stroke severity in anterior territory stroke (Level B) but possibly do not in vertebrobasilar artery territory stroke (Level C). Baseline DWI lesion volumes probably predict (final) infarct volumes (Level B) and possibly predict early and late clinical outcome measures (Level C). Baseline PWI volumes predict to a lesser degree the baseline stroke severity compared with DWI (Level C). There is insufficient evidence to support or refute the value of PWI in diagnosing acute ischemic stroke (Level U).

Whole brain and localized magnetization transfer measurements are associated with cognitive impairment in patients infected with human immunodeficiency virus.

BACKGROUND AND PURPOSE: Patients infected with human immunodeficiency virus (HIV) are susceptible to cognitive deterioration. This study investigated the utility of magnetization transfer (MT) imaging for quantification of brain tissue alterations associated with cognitive deficits in patients with HIV. MATERIALS AND METHODS: MT ratios (MTR) were derived for whole brain and for regions of interest (ROIs) in the basal ganglia and white matter in 11 HIV and 12 control subjects. Relationships with severity of cognitive impairment and specific neuropsychological deficits were also evaluated. RESULTS: MTR values for normalized whole brain histogram peak height, whole brain histogram mean, and all examined ROIs were reduced in the HIV subjects. Normalized histogram peak height and mean for whole brain, as well as means for the corpus callosum, basal ganglia, and frontal white matter (FWM), were significantly correlated with severity of cognitive impairment. MTR values for white matter regions (corpus callosum, FWM, and centrum semiovale) were correlated with specific cognitive deficits. CONCLUSION: Quantitative MTR measurements, determined for the whole brain and for vulnerable ROIs, are sensitive to neuropathologic changes associated with cognitive impairment in HIV-infected patients.

Monocyte chemoattractant protein-1 correlates with subcortical brain injury in HIV infection.

Various biomarkers have been suggested as associative or predictive of HIV-associated neurocognitive impairment. Plasma levels of monocyte chemoattractant protein 1 (MCP-1), tumor necrosis factor alpha (TNF-alpha), and hematocrit were evaluated for relationships with diffusion tensor imaging measurements of centrum semiovale, caudate, and putamen. MCP-1 levels correlated with tissue status (mean diffusivity) in all examined regions. Plasma markers were also significantly correlated with anisotropy measurements in centrum semiovale (TNF-alpha) and putamen (hematocrit).

Bone marrow diffusion measures correlate with dementia severity in HIV patients.

BACKGROUND AND PURPOSE: Escalation in monocyte trafficking from the bone marrow into the brain may play a critical role in central nervous system injury and cognitive deterioration in patients with HIV infection. This study tested the hypothesis that the mean diffusivity is sensitive to marrow changes in HIV patients and that these quantitative imaging measurements correlate with the severity of dementia. METHODS: The mean diffusivity (MD), determined for clival and calvarial marrow regions, was compared in 11 HIV-infected patients and 9 control subjects. The imaging measurements were also evaluated for relationships with dementia severity and markers of disease progression (CD4 and viral load in plasma). RESULTS: The MD was significantly reduced in both clival and calvarial marrow in HIV-infected patients (P =.006). Diffusion measurements for clival (P =.02) and for calvarial (P =.03) regions were significantly correlated with the severity of dementia. CONCLUSION: The results of this investigation support the utility of diffusion strategies for monitoring the marrow and provide further evidence of a relationship between marrow status changes and neurologic progression in HIV patients.

Diffusion alterations in corpus callosum of patients with HIV.

BACKGROUND AND PURPOSE: Diffusion alterations have been identified in the corpus callosum and frontal white matter of patients infected with human immunodeficiency virus (HIV), though the relevance of these findings to cognitive deterioration has not yet been determined. This study tested the hypothesis that diffusion tensor imaging can detect tissue status alterations in these regions in cognitively impaired patients infected with HIV and the acquired measurements correlate with the severity of cognitive impairment. METHODS: Fractional anisotropy (FA) and mean diffusivity (MD) were determined for corpus callosum (genu and splenium) and frontal white matter (FWM). The DTI measurements were compared in 11 HIV and 11 control participants. Patterns of relationship were examined with cognitive status measures from concurrent neurologic and neuropsychologic evaluations. RESULTS: FA values for the splenium were significantly reduced in the patients infected with HIV and correlated with dementia severity and deficits in motor speed. MD values for the splenium were significantly increased in the patients infected with HIV and correlated with deficits in motor speed. FA measurements were also significantly correlated with performance on visual memory (genu), visuoconstruction (FWM), and verbal memory (FWM) tasks. CONCLUSION: Diffusion abnormalities were identified in the splenium of the corpus callosum in patients infected with HIV, and these alterations were associated with dementia severity and motor speed losses. In vivo assessment of callosal integrity by using quantitative neuroimaging may have potential utility as a marker of brain injury in patients infected with HIV.

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.

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.

Contrast-enhanced MR angiography and perfusion imaging of the hand.

OBJECTIVE: The goal of this investigation was to develop a technique for producing high-resolution gadolinium-enhanced MR images of the hand that show three-dimensional angiographic anatomy and permit measurement of distal soft-tissue perfusion. CONCLUSION: High-resolution MR angiograms of the hand, as well as qualitative perfusion information, can be produced using a rapid sequential gadolinium-enhanced three-dimensional gradient-echo technique.

MR angiography using spin-lock flow tagging.

A method for MR angiography using an RF labeling technique is suggested. The method utilizes a slice-selective spin-lock pulse sequence for tagging the spins of inflowing blood. The pulse sequence begins with a spatially selective 90 degrees (x) RF pulse, followed by a nonselective composite locking pulse of 135 degrees (y) - n[360 degrees (y)]-135 degrees (y) and by a 90 degrees (-x) pulse. A spoiler gradient is then applied. A rapid imaging stage, which yields a T(1)rho-weighted signal from the tagged spins, completes the sequence. Untagged spins are thoroughly dephased and consequently suppressed in the image. Thus, contrast is obtained without an injection of a contrast material or image subtraction. Furthermore, the flow of the tagged bolus can be visualized. The sequence was implemented on phantoms and on human volunteers using a 1.5T scanner. The results indicate the feasibility of the suggested sequence.

Relationship between magnetic resonance arterial patency and perfusion-diffusion mismatch in acute ischemic stroke and its potential clinical use.

BACKGROUND: In patients with acute ischemic stroke the magnetic resonance (MR) perfusion-diffusion mismatch pattern (perfusion lesion at least 20% larger than the lesion on diffusion-weighted imaging) may indicate ischemically threatened but viable tissue. To our knowledge, the relationship of this MR pattern to serial changes in MR angiography (MRA) has not been reported. OBJECTIVES: To investigate the relationship between MRA changes and patterns of diffusion-weighted imaging and perfusion abnormalities and to determine if the information obtained could be used in clinical management. METHODS: The MR studies of 35 patients who had undergone sequential multimodality MR imaging studies within the first 4 days of stroke were reviewed. All lesions were in the internal carotid artery territory distribution. Magnetic resonance angiographies were read by 2 observers blinded to the clinical data. RESULTS: During the first 24 hours a perfusion-diffusion mismatch was present in 22 (92%) of the 24 patients with an MRA arterial occlusive lesion. (At this time 5 [46%] of the 11 patients with a normal MRA [P =.006] also had a mismatch.) Two to 4 days after stroke, of these 22 patients resolution of the mismatch occurred in 8 (87%) of 9 patients with recanalization on MRA compared with 5 (39%) of 13 patients without arterial recanalization (P =.03). Resolution of mismatch occurred in 3 (60%) of 5 patients with a normal MRA and a mismatch at the first time point. CONCLUSIONS: Concordance between MRA and the MR perfusion-diffusion mismatch pattern provides supportive evidence for an arterial vascular basis for this MR signature in acute stroke. Discordance between MRA lesions and mismatch may result from arterial branch occlusions undetected by MRA or from an alternate mechanism for the mismatch. The MR imaging patterns identified extend our understanding of the pathophysiology of stroke and may contribute to the improvement of stroke management in the future.

Evaluation of regional pulmonary perfusion using ultrafast magnetic resonance imaging.

An ultrafast MR sequence was used to measure changes in signal intensity during the first pass of intravascular contrast through the pulmonary circulation. From this, mean transit time, relative blood volume, and relative blood flow were calculated. Data were collected in an isogravitational plane in six healthy subjects. A slight but significant gradient in transit time was present, with faster times at the lung apex. A significant decrease in blood volume, compared with the lung base, was also seen in the apex. Significant decreases in blood volume and blood flow, compared with central portions of the lung, were seen in the lung periphery. Six additional subjects were imaged along a gravitational plane. A significant gradient in transit time was seen, with faster transit in dependent regions of the lung. MRI is able to evaluate regional differences in pulmonary perfusion with high spatial and temporal resolution. Magn Reson Med 46:166-171, 2001.

Technologic advances in abdominal MR imaging.

Magnetic resonance (MR) imaging is finding an ever-growing role in the evaluation of a wide range of conditions in the abdomen. No longer confined to problem solving regarding abnormalities in solid organs, such as the liver and kidneys, MR imaging is increasingly being applied to the evaluation of the pancreatic and biliary ductal systems and even the bowel. Recent technical advances in hardware and software have allowed the acquisition of MR images that are largely free of artifact secondary to bowel peristalsis or respiratory motion; images providing excellent anatomic detail can now be obtained routinely. Faster sequences have reduced image acquisition time, thereby improving patient acceptance and allowing more efficient utilization of machine time. New three-dimensional sequences allow rapid image acquisition, reducing section misregistration and motion artifact while improving multiplanar reformations. The potential of MR imaging to provide functional and anatomic information is intriguing, and new techniques, including diffusion and perfusion imaging, are being evaluated. This review considers the advances in imaging hardware and pulse sequence design that underlie the increasing role of MR imaging in evaluation of the abdomen and discusses evolving clinical applications.

Effect of lung inflation on arterial spin labeling signal in MR perfusion imaging of human lung.

The effect of lung inflation on arterial spin-labeling signal in lung perfusion is investigated. Arterial spin-labeling schemes, called alternation of selective inversion pulse (ASI) and its hybrid (HASI), which uses blood water as an endogenous, freely diffusible tracer, were applied to magnetic resonance (MR) perfusion imaging of the lung. Perfusion-weighted images of the lung from nine healthy volunteers were obtained at different time delays. There was a significant signal difference in ASI images acquired at different respiratory phases. Greater signal enhancement has been observed when the volunteers performed breath holding on end expiration than on end inspiration. This is in agreement with the normal physiologic effect of lung inflation on the pressure-flow relationship of pulmonary vasculature. ASI and HASI perfusion-weighted images show similar lung features and image quality. Preliminary results from pulmonary embolism patients indicate that arterial spin labeling is sensitive for the detection of areas of perfusion deficit. J. Magn. Reson. Imaging 2001;13:954-959.

Pulmonary ventilation: dynamic MRI with inhalation of molecular oxygen.

We have recently demonstrated a non-invasive technique to visualize pulmonary ventilation in humans with inhalation of molecular oxygen as a paramagnetic contrast agent. In the current study, T1 shortening of lung tissue by inhalation of oxygen was observed (P<0.001). The T1 values of lung tissue were also correlated with arterial blood oxygen pressure (PaO(2)) in a pig, resulting in excellent correlation (r(2)=0.997). Dynamic wash-in and wash-out MR ventilation images as well as dynamic wash-in wash-out signal intensity versus time curves were obtained. The mean wash-in decay constants were 26.8+/-10.5 s in the right lung, and 26.3+/-9.5 s in the left lung. The mean wash-out decay constants were 23.3+/-11.3 s in the right lung, and 20.8+/-10.5 s in the left lung. Dynamic assessment of pulmonary ventilation is feasible using oxygen-enhanced MR imaging, which could provide dynamic MR ventilation-perfusion imaging in combination with recently developed MR perfusion imaging technique, and thus a robust tool for the study of pulmonary physiology and pathophysiology.

Ultrafast MR grid-tagging sequence for assessment of local mechanical properties of the lungs.

While MR imaging with tagged magnetization has shown great utility in the study of muscle mechanics, the evaluation of pulmonary mechanics has long been hindered by the technical difficulties in MR imaging of lung parenchyma. In this study, a fast MR grid-tagging technique is described for dynamic assessment of regional pulmonary deformation. The method is based on a fast FLASH sequence with short TR and short TE. Tagging was achieved by using double DANTE pulse train or inversion pulses. Our results show that this technique is able to detect changes of the tagging grid caused by physiological deformation of the lung. Quantitative analysis of the data shows that this method is capable of assessing local pulmonary mechanics. The application of this technique could improve our understanding of ventilatory control, and thus provide a unique metric for assessing pulmonary disorders. Magn Reson Med 45:24-28, 2001.