Biomedical subjects

Richard Frayne

Publications and source records attributed to Richard Frayne.

At least 19 recordsLinked to original sources

PubMed2006

MR image reconstruction of sparsely sampled 3D k-space data by projection-onto-convex sets.

In many rapid three-dimensional (3D) magnetic resonance (MR) imaging applications, such as when following a contrast bolus in the vasculature using a moving table technique, the desired k-space data cannot be fully acquired due to scan time limitations. One solution to this problem is to sparsely sample the data space. Typically, the central zone of k-space is fully sampled, but the peripheral zone is partially sampled. We have experimentally evaluated the application of the projection-onto-convex sets (POCS) and zero-filling (ZF) algorithms for the reconstruction of sparsely sampled 3D k-space data. Both a subjective assessment (by direct image visualization) and an objective analysis [using standard image quality parameters such as global and local performance error and signal-to-noise ratio (SNR)] were employed. Compared to ZF, the POCS algorithm was found to be a powerful and robust method for reconstructing images from sparsely sampled 3D k-space data, a practical strategy for greatly reducing scan time. The POCS algorithm reconstructed a faithful representation of the true image and improved image quality with regard to global and local performance error, with respect to the ZF images. SNR, however, was superior to ZF only when more than 20% of the data were sparsely sampled. POCS-based methods show potential for reconstructing fast 3D MR images obtained by sparse sampling.

Algorithms↗

PubMed2006

Passive catheter visualization in magnetic resonance-guided endovascular therapy using multicycle projection dephasers.

PURPOSE: To improve upon the conventional projection dephaser (PD) method of background suppression and evaluate the use of multicycle projection dephasers to improve catheter conspicuity in background-suppressed MR images. MATERIALS AND METHODS: Passive visualization of endovascular catheters in MR images is compared using two background suppression techniques: 1) the conventional PD method and 2) the multicycle PD method. Contrast-filled 4-French (1.3 mm) catheters were imaged in homogeneous and heterogeneous phantoms, and in the common carotid artery of a canine using a modified spoiled gradient echo imaging sequence. We used catheter-to-background contrast (ranging from -100% to 100%) as the metric to compare background suppression techniques. RESULTS: In the homogeneous and heterogeneous phantoms, the contrast was -6.9% (catheter darker than background) and 15.0%, respectively, using the conventional PD method, and 50.6% and 44.0%, respectively, using the multicycle PD method. In the canine carotid artery, the contrast was -3.1% using the conventional PD method and 53.0% using the multicycle PD method. CONCLUSION: This work shows that multicycle projection dephasers improve catheter conspicuity over the conventional PD method. The multicycle PD method has potential for use in guiding endovascular procedures.

Animals↗

PubMed2006

Stroke imaging at 3.0 T.

Stroke is a devastating disease with a complex pathophysiology. It is a major cause of death and disability in North America. To fully characterize its extent and effects, one requires numerous specialized anatomical and functional MR techniques, specifically diffusion-weighted imaging, MR angiography, and perfusion-weighted imaging. The advent of 3.0 T clinical scanners has the potential to provide higher quality information in potentially less time compared with 1.5 T stroke-specific MR imaging protocols. This article gives a brief overview of stroke, presents the principles and clinical applications of the relevant MR techniques required for diagnostic stroke imaging at high field, and discusses the advantages, challenges, and limitations of 3.0 T imaging as they relate to stroke.

Brain↗

PubMed2006

MR angiography compared to conventional selective angiography in acute stroke.

BACKGROUND AND PURPOSE: Accuracy of intracranial magnetic resonance angiography (MRA) and reliability of interpretation are not well established compared to conventional selective catheter angiography. The purpose of this study was to determine the accuracy of MRA in evaluation of intracranial vessels in acute stroke and transient ischemic attack (TIA) patients METHODS: Twenty-nine patients (seven females, 22 males; median age 53) with acute stroke or TIA were enrolled into the study. All patients underwent both MRA using a 3 T clinical magnet and conventional angiography within 48 hours. Median time between MRA and angiography was 263 minutes. Conventional angiography preceded MRA in 15 cases. Fourteen patients received thrombolysis during MRA or angiography. National Institutes of Health Stroke Scale scores were obtained prior to the MR exam. One neuroradiologist rated all conventional angiograms, which were used as gold standard. Five observers, blinded to conventional angiography results and all clinical information except symptom side, rated the MR angiograms. Kappa statistics were used to assess reliability; contingency tables were used to assess accuracy of non-enhanced and enhanced MRA. RESULTS: Two hundred and fifty two intracranial vessels were assessed. Agreement between raters was good for both non-enhanced (kappa = 0.50) and gadolinium-enhanced (kappa = 0.46) images. There were a total of 26 vessels occluded by DSA. Overall, the non-enhanced MRA showed sensitivity of 84.2% (95% CI 60.4-96.6) and specificity of 84.6% (95% CI 78.6-89.4). The enhanced MRA showed sensitivity of 69.2 (95% CI 38.6-90.9) and specificity of 73.6 (95% CI 65.5-80.7). CONCLUSIONS: Magnetic resonance angiography is a good non-invasive screening tool for assessing intracranial vessel status in acute ischemic stroke. Angiography remains the gold standard for definitive assessment of the intracranial circulation.

Adolescent↗

PubMed2006

Acute ischemic stroke: accuracy of diffusion-weighted MR imaging--effects of b value and cerebrospinal fluid suppression.

PURPOSE: To prospectively determine which diffusion-weighted magnetic resonance (MR) imaging technique (ie, conventional diffusion-weighted MR imaging [b = 1000 or 1500 sec/mm2] or fluid-inversion prepared diffusion [FLIPD] MR imaging [b = 1500 sec/mm2]) is most accurate in depicting acute ischemic stroke at 3 T. MATERIALS AND METHODS: The Health Research Ethics Board approved this study; written informed consent was provided by all participants or their surrogate. Diffusion-weighted MR imaging was performed in 75 consecutive patients (43 men, 32 women; mean age, 64.0 years) with acute ischemic stroke. Two experienced neuroradiologists determined the presence of hyperacute stroke lesions at diffusion-weighted MR imaging by locating areas of hyperintensity that corresponded to regions with a decreased diffusion coefficient. These findings were used as the reference standard. Four raters who were blinded to patient history assessed all images and apparent diffusion coefficient maps for the presence of changes that were consistent with acute ischemic stroke. Accuracy, sensitivity, specificity, negative predictive value, positive predictive value, and inter- and intrarater reliability scores were calculated for each technique. RESULTS: Specificity, positive predictive value, and accuracy were not significantly different among the techniques. FLIPD MR images obtained with a b value of 1500 sec/mm2 had decreased sensitivity for acute ischemic stroke (mean, 61.8%; 95% confidence interval [CI]: 55.4%, 67.9%) compared with conventional diffusion-weighted MR images obtained with a b value of either 1000 sec/mm2 (mean, 82.5%; 95% CI: 77.1%, 87.0%) or 1500 sec/mm2 (mean, 84.5%; 95% CI: 79.3%, 88.9%). FLIPD MR images also had decreased negative predictive value (mean, 96.5%; 95% CI: 95.7%, 97.2%) compared with conventional diffusion-weighted MR images obtained with a b value of either 1000 sec/mm2 (mean, 98.4%; 95% CI: 97.8%, 98.8%) or 1500 sec/mm2 (mean, 98.6%; 95% CI: 98.1%, 99.0%). Intra- and interrater reliability scores were generally excellent for all three techniques. CONCLUSION: FLIPD MR images obtained with a b value of 1500 sec/mm2 are less suitable for the detection of acute ischemic stroke owing to a decreased sensitivity and negative predictive value. The performance of the two conventional diffusion-weighted MR imaging techniques (b = 1000 and 1500 sec/mm2) was equivalent.

Acute Disease↗

PubMed2006

Time-efficient breath-hold abdominal MRI at 3.0 T.

OBJECTIVE: The purpose of this study was to increase the allowed number of acquired slices per unit time (i.e., time efficiency) for high-power deposition breath-hold abdominal acquisitions at 3.0 T. MATERIALS AND METHODS: Abdominal MRI protocols include various T1-weighted, T2-weighted, and contrast-enhanced acquisitions that require extended spatial coverage and resolution. Ideally, each acquisition is completed within one breath-hold. At 3.0 T, power deposition (i.e., specific absorption rate [SAR]) concerns can limit achieving these conflicting needs because conventional sequences are based on 6-minute time-average SAR requirements. We optimized abdominal-specific sequences based on an approved short-term 10-second time-average SAR criterion and added a delay time after breath-holding to fulfill the long-term 6-minute time-average power deposition regulation. RESULTS: Using our strategy, image acquisition time efficiency at 3.0 T was increased approximately twofold compared with conventional abdominal breath-hold pulse sequences for 2D dual-echo gradient-recalled echo, single-shot fast spin-echo, and 3D steady-state free precession sequences. Volunteers experienced a slight sensation of warmth for the single-shot fast spin-echo implementation, the most SAR-intensive sequence. CONCLUSION: Our optimization strategy is not vendor-specific, is easily implemented for all conventional scanners (provided one can access and modify the pulse sequences directly, or the vendors can make the necessary changes), yields a higher slice-per-unit-time imaging efficiency, and still satisfies all the regulatory power deposition requirements.

Abdomen↗

PubMed2005

Control of end-tidal PCO2 reduces middle cerebral artery blood velocity variability: implications for physiological neuroimaging.

Breath-by-breath variability of the end-tidal partial pressure of CO2 (Pet(CO2)) has been shown to be associated with cerebral blood flow (CBF) fluctuations. These fluctuations can impact neuroimaging techniques that depend on cerebrovascular blood flow. We hypothesized that controlling Pet(CO2) would reduce CBF variability. Dynamic end-tidal forcing was used to control Pet(CO2) at 1.5 mm Hg above the resting level and to hold the end-tidal partial pressure of oxygen (Pet(O2)) at the resting level. Peak blood velocity in the middle cerebral artery (MCA) was measured by transcranial Doppler ultrasound (TCD) as an index of CBF. Blood velocity parameters and timing features were determined on each waveform and the variance of these parameters was compared between Normal (air breathing) and Forcing (end-tidal gas control) sessions. The variability of all velocity parameters was significantly reduced in the Forcing session. In particular, the variability of the average velocity over the cardiac cycle was decreased by 18.2% (P < 0.001). For the most part, the variability of the timing parameters was unchanged. Thus, we conclude that controlling Pet(CO2) is effective in reducing CBF variability, which would have important implications for physiologic neuroimaging.

Adult↗

PubMed2005

A new method of creating intervertebral disc disruption of various grades.

BACKGROUND: The purpose of this study was to develop a model of intervertebral disc disruption capable of (1) internal disruption without excessive disruption to the disc surface, (2) user-defined disruption magnitude and location and (3) interrogation by magnetic resonance imaging. Present models of disc disruption may have some, but not all, of these features. METHODS: Intravenous tubes were inserted into the intervertebral discs of a cadaveric porcine lumbar spine. Tube placement in the inner annulus was confirmed by magnetic resonance imaging. Each disc was then injected through the intravenous tube with nitrogen gas at pressures of 69 kPa, 172 kPa, 345 kPa and 690 kPa. Before and after injection, edge detection analysis of magnetic resonance imaging images was used to quantify tissue disruption. These values were then multiplied by the thickness of the slices and summed to determine disruption volume for individual discs. Four additional discs were injected with the addition of ink, sectioned and then inspected visually. RESULTS: As the injection pressure increased, the gas volume within the annulus increased significantly as did visualized annular disruption. No significant difference in gas volume was observed between different discs injected with equal pressure. INTERPRETATION: As confirmed by magnetic resonance imaging and dissection, gas volume and tissue disruption within the annulus fibrosus were proportional to the pressure of injected nitrogen. This model of disc disruption promises to provide several advantages in the investigation of disc pathology including (1) user-controlled magnitude of inner annulus disruption, (2) user-controlled tissue disruption localization, (3) minimal disruption of the exterior annulus, (4) independence between the magnitude of external and internal disruption and (5) the ability to visualize resulting disruptions with magnetic resonance imaging.

Animals↗

PubMed2005

Reassessing the clinical efficacy of two MR quantitative DSC PWI CBF algorithms following cross-calibration with PET images.

Clinical cerebral blood flow (CBF) maps generated through dynamic- susceptibility contrast (DSC) magnetic resonance (MR) perfusion imaging are currently cross-calibrated with PET studies. The cross-calibration is achieved by rescaling the MR CBF values so that normal white matter CBF corresponds to 22 ml/100 g/min. Examples are provided in this paper to show how this rescaling procedure changes both the clinical interpretation of CBF maps and the manner by which the performance of a given deconvolution algorithm should be assessed. (i) Singular-value decomposition-based (SVD) algorithms produce absolute CBF estimates that are inherently under-estimated for all tissue mean transit times (MTT) but, after rescaling, will generate CBF maps that are over-estimated for MTT >4.8 s. (ii) In principle, frequency-domain modelling techniques are expected to be inherently less sensitive to contrast recirculation biases than the time-domain SVD algorithms. However, it is shown that both CBF algorithms become greatly less sensitive to distortions from recirculation after clinical cross-calibration through rescaling has been performed. It is concluded that, when rescaling procedures are employed, it is relatively more important to develop deconvolution algorithms that produce CBF estimates with accuracies that vary little with MTT than to produce algorithms that provide inherently more accurate CBF estimates, but whose relative accuracy varies significantly with MTT.

Algorithms↗

PubMed2005

The impact of partial-volume effects in dynamic susceptibility contrast magnetic resonance perfusion imaging.

PURPOSE: To demonstrate the degree of the cerebral blood flow (CBF) estimation bias that could arise from distortion of the arterial input function (AIF) as a result of partial-volume effects (PVEs) in dynamic susceptibility contrast (DSC) magnetic resonance imaging (MRI). MATERIALS AND METHODS: A model of the volume fraction an artery occupies in a voxel was devised, and a mathematical relationship between the amount of PVE and the measured baseline MR signal intensity was derived. Based on this model, simulation studies were performed to assess the impact of PVE on CBF. Furthermore, the effectiveness of linear PVE compensation approaches on the concentration function was investigated. RESULTS: Simulation results showed a nonlinear relationship between PVE and the resulting CBF measurement error. In addition to AIF underestimation, PVE also causes distortions of AIF frequency characteristics, leading to CBF errors varying with mean transit time (MTT). An uncorrected AIF measured at a voxel with a partial-volume fraction of <or=50% could produce a CBF overestimation of more than fourfold. Linear compensation of the concentration curves did not produce correct CBF estimates. CONCLUSION: PVE can induce significant CBF estimation biases. In addition, the MTT dependence of CBF accuracy raises doubts of the validity of adopting a single cross-calibration factor (i.e., setting normal white matter to 22 mL minute(-1) (100 g)(-1)) to obtain CBF values with absolute units. The impact of PVE may be reduced by decreasing the maximum arterial signal drop in the perfusion images. To correct the AIF distortions introduced by PVE, the nonlinear relationship between the impact of PVE on MR signal intensity and contrast concentration function must be considered.

Calibration↗

PubMed2005

Advantages of frequency-domain modeling in dynamic-susceptibility contrast magnetic resonance cerebral blood flow quantification.

In dynamic-susceptibility contrast magnetic resonance perfusion imaging, the cerebral blood flow (CBF) is estimated from the tissue residue function obtained through deconvolution of the contrast concentration functions. However, the reliability of CBF estimates obtained by deconvolution is sensitive to various distortions including high-frequency noise amplification. The frequency-domain Fourier transform-based and the time-domain singular-value decomposition-based (SVD) algorithms both have biases introduced into their CBF estimates when noise stability criteria are applied or when contrast recirculation is present. The recovery of the desired signal components from amid these distortions by modeling the residue function in the frequency domain is demonstrated. The basic advantages and applicability of the frequency-domain modeling concept are explored through a simple frequency-domain Lorentzian model (FDLM); with results compared to standard SVD-based approaches. The performance of the FDLM method is model dependent, well representing residue functions in the exponential family while less accurately representing other functions.

Algorithms↗

PubMed2005

Orientation of tendons in vivo with active and passive knee muscles.

Tendon orientations in knee models are often taken from cadaver studies. The aim of this study was to investigate the effect of muscle activation on tendon orientation in vivo. Magnetic resonance imaging (MRI) images of the knee were made during relaxation and isometric knee extensions and flexions with 0 degrees , 15 degrees and 30 degrees of knee joint flexion. For six tendons, the orientation angles in sagittal and frontal plane were calculated. In the sagittal plane, muscle activation pulled the patellar tendon to a more vertical orientation and the semitendinosus and sartorius tendons to a more posterior orientation. In the frontal plane, the semitendinosus had a less lateral orientation, the biceps femoris a more medial orientation and the patellar tendon less medial orientation in loaded compared to unloaded conditions. The knee joint angle also influenced the tendon orientations. In the sagittal plane, the patellar tendon had a more anterior orientation near full extension and the biceps femoris had an anterior orientation with 0 degrees and 15 degrees flexions and neutral with 30 degrees flexions. Within 0 degrees to 30 degrees of flexion, the biceps femoris cannot produce a posterior shear force and the anterior angle of the patellar tendon is always larger than the hamstring tendons. Therefore, co-contraction of the hamstring and quadriceps is unlikely to reduce anterior shear forces in knee angles up to 30 degrees . Finally, inter-individual variation in tendon angles was large. This suggests that the amount of shear force produced and the potential to counteract shear forces by co-contraction is subject-specific.

Adult↗

PubMed2005

An alternative viewpoint of the similarities and differences of SVD and FT deconvolution algorithms used for quantitative MR perfusion studies.

Quantitative cerebral blood flow (CBF) values can be determined from residue function estimates obtained from magnetic resonance dynamic susceptibility contrast (DSC) perfusion studies using a variety of deconvolution approaches. However, there are significant differences between the CBF estimates obtained, differences that are not simply due to minor details of the implementation of the algorithms. The standard singular value decomposition (sSVD) shows a variation of CBF values with arterial-tissue delay (ATD) not present with the Fourier transform deconvolution algorithm. Fourier transform deconvolution and the newly suggested delay-invariant SVD algorithm implementations provide CBF estimates whose accuracy changes with tissue mean transit times (MTTs). Techniques combining sSVD with deliberate ATD manipulation have been proposed to compensate for this inaccuracy. Other studies indicate that CBF changes related to slice position in a multislice study, and other experimental factors, can be reduced using interpolative deconvolution algorithms. In this review, we use both time-domain and frequency-domain analysis to show the underlying theoretical relationships between these many approaches to obtain "the best" CBF estimate. This model allows us to better understand the similarities and differences, advantages and disadvantages between these variants of the deconvolution algorithms used in DSC perfusion studies.

Algorithms↗

PubMed2005

A novel method to derive separate gray and white matter cerebral blood flow measures from MR imaging of acute ischemic stroke patients.

Perfusion-weighted imaging (PWI) measures can predict tissue outcome in acute ischemic stroke. Accuracy might be improved if differential tissue susceptibility to ischemia is considered. We present a novel voxel-by-voxel analysis to characterize cerebral blood flow (CBF) separately in gray (GM) and white matter (WM). Ten patients were scanned with inversion-recovery spin-echo EPI (IRSEPI), diffusion-weighted imaging (DWI), PWI<6 h from onset and fluid attenuated inversion-recovery (FLAIR) at 30 days. Image processing included coregistration to PWI, automatic segmentation of IRSEPI into GM, WM and CSF and semiautomatic segmentation of DWI/FLAIR to derive the acute and 30-day lesions. Five tissue compartments were defined: (1) 'Core' (abnormal acutely and at 30 days), (2) 'Growth' (or 'infarcted penumbra', abnormal only at 30 days), (3) 'Reversed' (abnormal acutely but normal at 30 days), (4) 'MTT-Delayed ' (tissue with delayed mean transit time but not part of the acute or 30-day lesion), and (5) 'Normal' brain. Cerebral blood flow in GM and WM of each compartment was obtained from quantitative maps. Gray matter and WM mean CBF in the growth region differed by 5.5 mL/100 g min (P=0.015). Mean CBF also differed significantly within normal and MTT-Delayed compartments. The difference in the reversed region approached statistical significance. In core, GM and WM CBF did not differ. The results suggest separate ischemic thresholds for GM and WM in stroke penumbra.

Aged↗

PubMed2005

MR perfusion and diffusion in acute ischemic stroke: human gray and white matter have different thresholds for infarction.

It is thought that gray and white matter (GM and WM) have different perfusion and diffusion thresholds for cerebral infarction in humans. We sought to determine these thresholds with voxel-by-voxel, tissue-specific analysis of co-registered acute and follow-up magnetic resonance (MR) perfusion- and diffusion-weighted imaging. Quantitative cerebral blood flow (CBF), cerebral blood volume (CBV), mean transit time (MTT), and apparent diffusion coefficient (ADC) maps were analyzed from nine acute stroke patients (imaging acquired within 6 h of onset). The average values of each measure were calculated for GM and WM in normally perfused tissue, the region of recovered tissue and in the final infarct. Perfusion and diffusion thresholds for infarction were determined on a patient-by-patient basis in GM and WM separately by selecting thresholds with equal sensitivities and specificities. Gray matter has higher thresholds for infarction than WM (P<0.009) for CBF (20.0 mL/100 g min in GM and 12.3 mL/100 g min in WM), CBV (2.4 mL/100 g in GM and 1.7 mL/100 g in WM), and ADC (786 x 10(-6) mm(2)/s in GM and 708 x 10(-6) mm(2)/s in WM). The MTT threshold for infarction in GM is lower (P=0.014) than for WM (6.8 secs in GM and 7.1 secs in WM). A single common threshold applied to both tissues overestimates tissue at risk in WM and underestimates tissue at risk in GM. This study suggests that tissue-specific analysis of perfusion and diffusion imaging is required to accurately predict tissue at risk of infarction in acute ischemic stroke.

Aged↗

PubMed2004

A comparison of images generated from diffusion-weighted and diffusion-tensor imaging data in hyper-acute stroke.

PURPOSE: To compare isotropic (combined diffusion-weighted image [CMB], apparent diffusion coefficient [ADC], TRACE, exponential ADC [eADC], and isotropically-weighted diffusion image [isoDWI]) and anisotropic (relative anisotropy [RA], fractional anisotropy [FA], and volume ratio [VR]) diffusion images collected with fast magnetic resonance (MR) diffusion-weighted (DWI) and diffusion-tensor (DTI) acquisition strategies (each less than one minute) in hyper-acute stroke. MATERIALS AND METHODS: Twenty-one patients suffering from ischemic stroke-imaged within six hours of symptom onset using both DWI and DTI-were analyzed. Regions of interest were placed in the ischemic lesion and in normal contralateral tissue and the percent difference in image intensity was calculated for all nine generated images. RESULTS: The average absolute percent changes for the isotropic strategies were all > 38%, with isoDWI found to have a difference of 50.7% +/- 7.9% (mean +/- standard error, P < 0.001). The ADC maps had the most significant difference (-42.4% +/- 2.0%, P < 0.001, coefficient of variation = 0.22). No anisotropic images had significant differences. CONCLUSION: Anisotropic maps do not consistently show changes in the first six hours of ischemic stroke; therefore, isotropic maps, such as those obtained using DWI, are more appropriate for detecting hyper-acute stroke. Anisotropic images, however, may be useful to differentiate hyper-acute stroke from acute and sub-acute stroke.

Aged↗

PubMed2003

Reliability of assessing percentage of diffusion-perfusion mismatch.

BACKGROUND AND PURPOSE: Emergent neurovascular imaging holds promise in identifying new and optimum target populations for thrombolysis in stroke. Recent research has focused on patients with diffusion-weighted MRI (DWI)-perfusion-weighted MRI (PWI) mismatch as a marker of tissue at risk of infarction and a means to select the most suitable candidates for thrombolysis. The present study sought to estimate the reliability of assessing the percentage of DWI-PWI mismatch. METHODS: Thirteen patients with acute strokes had DWI and PWI within 7 hours of symptom onset. Six raters independently created relative mean transit time (rMTT) maps and then compared them with DWI images to assess the percentage of mismatch (PWI>DWI) in 10% increments. The MR scans were reassessed by 4 raters, tracing around the lesions to calculate the volume percentage of mismatch. RESULTS: Visual assessment had an interrater reliability of 0.68 (95% CI, 0.52 to 1.0; SEM=21.6%) and an intrarater reliability of 0.80 (95% CI, 0.47 to 1.0; SEM=16.9%). Hand-drawn assessment had an interrater reliability of 0.66 (95% CI, 0.45 to 1.0; SEM=26.2%) and an intrarater reliability of 0.94 (95% CI, 0.81 to 1.0; SEM=10.9%). CONCLUSIONS: Results from the present study suggest that quantifying mismatch by the human eye is reproducible but not reliable among observers. This raises doubts about using mismatch for clinical decision making and clinical trial enrollment.

Acute Disease↗

PubMed2003

Signal-to-noise ratio effects in quantitative cerebral perfusion using dynamic susceptibility contrast agents.

Theoretical and simulation evidence is presented in support of the idea that the optimal manner of determining blood flow from MR perfusion studies is not necessarily obtained by setting experimental conditions to maximize either the arterial input or the measured tissue concentration level for a particular echo time (TE). The noise power in the contrast concentration curve is associated with its peak because of the nonlinear relationship between the contrast concentration and MR signal intensity curves. The optimum signal-to-noise ratio (SNR), SNR(C), for a particular contrast concentration curve can be obtained when the experimental concentration level and TE are adjusted to produce an MR intensity curve whose signal loss is 63% of the precontrast MR signal intensity. It is demonstrated that the stability of the singular valued decomposition (SVD) deconvolution approach to determine blood flow parameters is increased when the tissue curve maximum signal loss is in the range of 40-80%. The accuracy and stability of the SVD-determined blood flow parameters are affected by deviations from these optimum conditions in a manner that depends on the mean transit time (MTT) associated with the residue function. It is recommended that the experimental TE value be set so that neither the tissue nor the arterial curves are placed a region of rapidly deteriorating SNR(C).

Blood Flow Velocity↗