Association between internal carotid artery dissection and arterial tortuosity.

INTRODUCTION: Carotid artery dissection is an important cause of ischemic stroke in all age groups, particularly in young patients. The purpose of this work was to assess whether there is an association between the presence of an internal carotid artery dissection (ICAD) and the arterial tortuosity. METHODS: This study considered 124 patients (72 males and 52 females; median age 57 years) with CT/MR diagnosis of ICAD of the internal carotid artery were considered in this multi-centric retrospective study. The arterial tortuosity was evaluated and, when present, was categorized as elongation, kinking, or coiling. For each patient, both the right and left sides were considered for a total number of 248 arteries in order to have the same number of cases and controls. Fisher's exact test was applied to test the association between elongation, kinking, coiling, dissection, and the side affected by CAD. RESULTS: Fisher's exact test showed a statistically significant association between the ICAD and kinking (p = 0.0089) and coiling (p = 0.0251) whereas no statistically significant difference was found with arterial vessel elongation (p = 0.444). ICAD was more often seen on the left side compared to the right (p = 0.0001). These results were confirmed using both carotid arteries of the same patient as dependent parameter with p = 0.0012, 0.0129, and 0.3323 for kinking, coiling, and elongation, respectively. CONCLUSION: The presence of kinking and coiling is associated with ICAD.

Trends in lumbar puncture over 2 decades: a dramatic shift to radiology.

OBJECTIVE: The purpose of this study is to evaluate national trends in lumbar puncture (LP) procedures and the relative roles of specialty groups providing this service. MATERIALS AND METHODS: Aggregated claims data for LPs were extracted from Medicare Physician Supplier Procedure Summary master files annually from 1991 through 2011. LP procedure volumes by specialty group and place of service were studied. RESULTS: Between 1991 and 2011, the overall numbers of LP procedures increased, with a slight increase in diagnostic LP procedures (90,460 vs 90,785) and a marked increase in therapeutic LP procedures (2868 vs 6461) in Medicare fee-for-service beneficiaries. Although radiologists performed 11.3% (n = 10,533) of all LP procedures in 1991, they performed 46.6% (n = 45,338) in 2011. For diagnostic LPs, radiology (11.4% [n = 10,272] in 1991 and 48.0% [n = 43,601] in 2011) now exceeds emergency medicine, neurosciences, and all others as the dominant provider group. For therapeutic LP procedures, radiology now performs the second greatest number of LP procedures (9.0% [n = 261] in 1991 and 26.9% [n = 1737] in 2011). Although volumes remain small (< 10% of all procedures), midlevel practitioners have experienced over 100-fold growth for most services. The inpatient hospital setting remains the dominant site of service (71,385 in 1991 vs 44,817 in 2011: -37%), followed by procedures performed in the emergency department (297 in 1991 vs 26,117 in 2011: 8794%). CONCLUSION: Over the last 2 decades, LP procedures on Medicare beneficiaries have increased, with radiology now the dominant overall provider. Although this trend may have relatively negative financial implications for radiology practices in current fee-for-service payment models, it has the potential to cement radiology's more central position through direct involvement in patient care in emerging accountable care organizations.

T1-weighted MRI as a substitute to CT for refocusing planning in MR-guided focused ultrasound.

Precise focusing is essential for transcranial MRI-guided focused ultrasound (TcMRgFUS) to minimize collateral damage to non-diseased tissues and to achieve temperatures capable of inducing coagulative necrosis at acceptable power deposition levels. CT is usually used for this refocusing but requires a separate study (CT) ahead of the TcMRgFUS procedure. The goal of this study was to determine whether MRI using an appropriate sequence would be a viable alternative to CT for planning ultrasound refocusing in TcMRgFUS. We tested three MRI pulse sequences (3D T1 weighted 3D volume interpolated breath hold examination (VIBE), proton density weighted 3D sampling perfection with applications optimized contrasts using different flip angle evolution and 3D true fast imaging with steady state precision T2-weighted imaging) on patients who have already had a CT scan performed. We made detailed measurements of the calvarial structure based on the MRI data and compared those so-called 'virtual CT' to detailed measurements of the calvarial structure based on the CT data, used as a reference standard. We then loaded both standard and virtual CT in a TcMRgFUS device and compared the calculated phase correction values, as well as the temperature elevation in a phantom. A series of Bland-Altman measurement agreement analyses showed T1 3D VIBE as the optimal MRI sequence, with respect to minimizing the measurement discrepancy between the MRI derived total skull thickness measurement and the CT derived total skull thickness measurement (mean measurement discrepancy: 0.025; 95% CL (-0.22-0.27); p = 0.825). The T1-weighted sequence was also optimal in estimating skull CT density and skull layer thickness. The mean difference between the phase shifts calculated with the standard CT and the virtual CT reconstructed from the T1 dataset was 0.08 ± 1.2 rad on patients and 0.1 ± 0.9 rad on phantom. Compared to the real CT, the MR-based correction showed a 1 °C drop on the maximum temperature elevation in the phantom (7% relative drop). Without any correction, the maximum temperature was down 6 °C (43% relative drop). We have developed an approach that allows for a reconstruction of a virtual CT dataset from MRI to perform phase correction in TcMRgFUS.

Assessment of collateral flow in patients with cerebrovascular disorders.

The ability to maintain cerebral parenchymal perfusion during states of acute or chronic ischemic insult depends largely on the capacity of the cerebral collateral circulation. Perfusion techniques, including perfusion-CT and arterial spin labeling, may not only describe the overall status of the collateral network, but can also quantify the pathophysiologic collateral reserve, which is occult to conventional imaging techniques. The following review details advanced imaging modalities capable of resolving pathophysiologic collateral circulation in a functional and dynamic manner, with regards to the evaluation of both acute ischemic penumbra and chronic cerebral vascular reserve. Specifically, the applications of perfusion-CT, arterial spin labeling MRI techniques, and transcranial Doppler are reviewed in the context of collateral circulation with emphasis on perfusion techniques and proposed clinical utility.

Trans-illuminated laser speckle imaging of collateral artery blood flow in ischemic mouse hindlimb.

The mouse ischemic hindlimb model is used widely for studying collateral artery growth (i.e., arteriogenesis) in response to increased shear stress. Nonetheless, precise measurements of regional shear stress changes along individual collateral arteries are lacking. Our goal is to develop and verify trans-illumination laser speckle flowmetry (LSF) for this purpose. Studies of defibrinated bovine blood flow through tubes embedded in tissue-mimicking phantoms indicate that trans-illumination LSF better maintains sensitivity with an increasing tissue depth when compared to epi-illumination, with an ∼50% reduction in the exponential decay of the speckle velocity signal. Applying trans-illuminated LSF to the gracilis muscle collateral artery network in vivo yields both improved sensitivity and reduced noise when compared to epi-illumination. Trans-illuminated LSF images reveal regional differences in collateral artery blood velocity after femoral artery ligation and are used to measure an ∼2-fold increase in the shear stress at the entrance regions to the muscle. We believe these represent the first direct measurements of regional shear stress changes in individual mouse collateral arteries. The ability to capture deeper vascular signals using a trans-illumination configuration for LSF may expand the current applications for LSF, which could have bearing on determining how shear stress magnitude and direction regulate arteriogenesis.

Laser speckle flowmetry method for measuring spatial and temporal hemodynamic alterations throughout large microvascular networks.

OBJECTIVES: 1) To develop and validate laser speckle flowmetry (LSF) as a quantitative tool for individual microvessel hemodynamics in large networks. 2) To use LSF to determine if structural differences in the dorsal skinfold microcirculation (DSFWC) of C57BL/6 and BALB/c mice impart differential network hemodynamic responses to occlusion. METHODS: We compared LSF velocity measurements with known/measured velocities in vitro using capillary tube tissue phantoms and in vivo using mouse DSFWCs and cremaster muscles. Hemodynamic changes induced by feed arteriole occlusion were measured using LSF in DSFWCs implanted on C57BL/6 and BALB/c mice. RESULTS: In vitro, we found that the normalized speckle intensity (NSI) versus velocity linear relationship (R(2) ≥ 0.97) did not vary with diameter or hematocrit and can be shifted to meet an expected operating range. In vivo, DSFWC and cremaster muscle preparations (R(2) = 0.92 and 0.95, respectively) demonstrated similar linear relationships between NSI and centerline velocity. Stratification of arterioles into predicted collateral pathways revealed significant differences between C57BL/6 and BALB/c strains in response to feed arteriole occlusion. CONCLUSIONS: These data demonstrate the applicability of LSF to intravital microscopy microcirculation preparations for determining both relative and absolute hemodynamics on a network-wide scale while maintaining the resolution of individual microvessels.