Suna Sumer

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

Please cite this paper as: Meisner JK, Sumer S, Murrell KP, Higgins TJ, Price RJ. Laser speckle flowmetry method for measuring spatial and temporal hemodynamic alterations throughout large microvascular networks. Microcirculation 19: 619–631, 2012.

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.

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 radiologys more central position through direct involvement in patient care in emerging accountable care organizations.

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

Abstract. 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.

Utilizing dual energy CT to improve CT diagnosis of posterior fossa ischemia.

BACKGROUND AND PURPOSE Evaluation of posterior fossa ischemia on conventional CT is limited. The goal of our study was to determine if virtual monochromatic CT increases the diagnostic accuracy for the detection of posterior infarcts relative to standard CT while using diffusion-weighted MRI as a reference standard. METHODS Thirty consecutive subjects who meet the following inclusion criteria were retrospectively enrolled: (1) symptoms of posterior fossa stroke (e.g. vertigo, fainting, and dizziness), (2) unenhanced dual-energy CT of the head performed upon admission to the emergency department, and (3) MRI of the brain within 7 days following the CT. Eight of the 30 subjects were determined to have MRI diffusion-weighted imaging findings consistent with acute posterior fossa ischemia. Monochromatic energy reconstructions at 60, 80, 100, 120keV and the clinical CT were interpreted independently by two fellowship-trained neuroradiologists, who assessed the images for posterior fossa infarcts and for imaging quality. RESULTS Reconstructions obtained at 80keV provided the best artifact reduction and overall maximization of image quality and were statistically significantly better than standard head CT (P<0.001). Sensitivity, specificity, positive predictive value, and negative predictive value were at least not less than standard CT, and there was a trend toward better values at 100keV (P=0.096). CONCLUSION Monoenergetic 80 or 100keV reconstructions may improve the detection of posterior fossa ischemia compared to conventional CT. However, if clinical suspicion for posterior fossa ischemia warrants, a brain MRI with diffusion-weighted imaging should still be obtained, even in the presence of a negative dual energy CT of the brain.

T1-weighted MRI as a substitute to CT for skull aberration correction in transcranial focused ultrasound: in vivo feasibility and in vitro comparison on human calvaria

CT scans have been used to refocus ultrasound for clinical transcranial MRI-guided focused ultrasound (TcMRgFUS). The refocusing of the ultrasound arrays is a crucial step in TcMRgFUS therapy because skulls distort sound beams due to the ununiformed shape and composition of the bone. CT scan based algorithms have been developed to estimate the phase shifts induced by the bone. The corresponding phase conjugated signals are then emitted by ultrasound arrays to be refocused on brain targets through the skull. However, CT scans elongate the TcMRgFUS treatment process and expose patients to ionizing radiation. This study tested three different MRI pulse sequences (T1, T2, and proton density) against CT to determine if MRI data could be a viable alternative to CT for planning ultrasound refocusing in TcMRgFUS.