Normal-Pressure Hydrocephalus - International Hydrocephalus ...

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a. b. c.To rectify these shortcomings, atechnique has been developed thatdirectly quantifies the volume of CSFflowing through the aqueduct. Previousstudies have shown that this CSFmotion is pulsatile, with a small netcraniocaudal component; the parameterwe measured was the aqueductalCSF stroke volume. This is defined asthe average of the volume of CSFmoving craniocaudad during systoleand that moving caudocraniad duringdiastole. It is derived from measurementson phase-contrast CSF velocityMR images (26). Specifically, it is theproduct of the measured velocity of apixel (in millimeters per second) andthe area of that pixel (in square millimeters)integrated over the cross-sectionalarea of the aqueduct integratedin time over mechanical systole ordiastole.The units of the aqueductal CSFstroke volume are thus cubic millimeterson microliters. The purposes ofthis study were to compare the efficaciesof using measurements of aqueductalCSF stroke volume and aqueductalCSF flow void on routine MRimages as predictors of shunt responsein patients with clinical NPH.MATERIALS AND METHODSd. e.Figure 1. Images and data obtained in an 83-year-old man (patient 8) with clinical NPH, intermediateCSF flow void, elevated aqueductal CSF stroke volume (82 p.L), and favorable responseto VP shunting. (a-e) Proton-density-weighted axial spin-echo MR images (3,000/22)demonstrate a moderate (score of 2) CSF flow void (arrow in b-cl). (Fig 1 continues.)In 42 consecutive patients with clinical,lumbar puncture, and routine MR imagingfindings suggestive of NPH, aqueductalCSF stroke volumes were measured bymeans of CSF velocity MR imaging. Ofthese 42 patients, 18 underwent ventriculoperitoneal(VP) shunt formation becauseof the results of the CSF flow study, severityof NPH symptoms, and presence ofcoexisting disease. The study populationcomprises eight men and 10 women aged54-83 years (mean age, 73 years).Spin-echo, proton-density-weightedaxial MR imaging was performed with eithera 1.5-T Siemens Magnetom 63SP orSP4000 (3,000/22 [repetition time msec/echo time msec]; Siemens Medical Systems,Erlangen, Germany) or a 1.5-T GESigna Advantage 5x (3,000/30; GE MedicalSystems, Milwaukee, Wis). Imaging parameterswere a standard 192 x 256 matrix,a 22-cm field of view, 20 sections, anda 5-mm section thickness. Intersection gapwas 1.5 or 2.5 mm for the Siemens or GEsystem, respectively. First-order flow compensationin the readout and section-selectdirections was used in all sequences.Aqueductal flow voids were scored blindly(Table 1) by an MR imaging-trained radiologist(D.S.) on a scale of 0-4 (Figs 1-3) accordmgto a method similar to that used in a previousstudy (25): 0 indicated no signal loss; 1,signal loss confined to the aqueduct and upperfourth ventride; 2, signal loss extendingfrom the posterior third to the upper fourthventrides; 3, signalloss extending to the postetiorthird ventricle and middle fourth yentmicle;and 4, signal loss extending from theforamen of Monro to the obex of the fourthventricle. In the previous study (25), flowvoids were scored as 0 and 1 in healthy controlsubjects and in patients who did not respondto shunting, while prominent flowvoids were scored as 2-4 in patients withNPH who responded to shunting.The techniques for CSF velocity MR imagingused in the current study have beendescribed in detail previously (26). All CSFflow MR studies were performed with theSiemens system by using a modified, twodimensional,fast imaging with steadystateprecession (FISP) sequence (100/16;flip angle, 15#{176}) with a section thickness of 4mm and positioning of the section perpendicularto the aqueduct (Fig 1). Flow encodingwas used in the section-select directionby using an aliasing velocity of 200mm/sec. A 512 x 512 matrix and a 160-mmfield of view were used, which resulted inan in-plane spatial resolution of 0.3125mm. The loss of signal-to-noise ratio resultingfrom use of such small pixels was524 #{149} Radiology February 1996
f. g. h.1. j.Figure 1 (continued). (f) Sagittal, scout, TI-weighted, spin-echo MR image (500/15) demonstratesposition of section for assessing CSF flow through the aqueduct. (g) Magnitude FISPMR image (100/16; 15#{176} flip angle) obtained during CSF flow study demonstrates aqueduct(arrow). (h) Phase-contrast FISP MR image (100/16; 15#{176} flip angle) obtained during systoledemonstrates craniocaudal flow (arrow; whitest areas = 200 mm/sec craniocaudal). (1) PhasecontrastFISP MR image (100/16; 15#{176} flip angle) obtained during diastole demonstrates caudocranialflow (arrow; blackest areas = 200 mm/sec caudocranial). (j) Plots of mean velocity (millimetersper second; upper left), peak velocity (millimeters per second; upper right), andvolumetric flow rate (cubic millimeters per second; lower left) as functions of the cardiac cycle(milliseconds). Peak velocity plot demonstrates aliasing.Findings of previous studies (27) in whicha pulsatile flow phantom has been usedhave verified the accuracy of the aqueductalCSF stroke volume measurement whileshowing that the peak velocity measurementsare particularly sensitive to noise(Figlj).Clinical data were collected from chartreview and discussion with clinicians. Apositive response to shunting was definedas any substantial clinical functional improvement,even if not all symptoms werealleviated. For example, patient 6 (Table1), who was nonambulatory before shunting,became ambulatory and had decreasedurinary incontinence after surgery. Althoughthis patient had no improvement in his substantialdementia, these other improvementsallowed his family to provide care at homeand alleviated the need for skilled nursing.Thus, this was considered a positive outcome.This mixed response, however, wasatypicaL In most patients, there was eitherobvious improvement or clearly no substantialchange; thus, differentiation betweenpositive and negative responses to shuntingwas, in most cases, not difficult.partially compensated for by reducing thebandwidth from 130 Hertz per pixel to 78Hertz per pixel. Use of a half-Fourier algorithm(with 16 lines of oversampling)helped to keep the measurement timewithin reason (14 minutes). The CSF yelocitydata ultimately used to calculate theaqueductal CSF stroke volume were obtamedfrom these images.Continuous data acquisition and retrospectivecardiac gating with electrocardiographicleads were used to allow evaluationof CSF velocity during the entirecardiac cycle (26). Thirty-two flow-encodedacquisitions were obtained in 3.2seconds (usually three or four cardiaccycles) before advance of the phase-encodinggradient. Data were then retmospectivelysorted into 18 cine frames spanningthe complete cardiac cycle. A “zerovelocity”reference image was calculatedby averaging all the phase measurementson each of the phase images with the assumptionof zero net flow through theaqueduct of Sylvius during one cardiaccycle. The phase measurements on thiszero-velocity reference image were thensubtracted from the phase measurementson each of the phase images to produce 18phase-contrast, CSF velocity MR images.While this assumption of zero net flowclearly introduces some error, the magnitudeof the error has been shown to beless than 5% in healthy control subjectsand considerably less than 5% in patientswith hydrocephalus, because more than95% of the volumetric flow during onecardiac cycle is to-and-fro (26).Software was developed to determinethe mean and peak velocities and the volumetricflow rate through the aqueduct asa percentage of the cardiac cycle (Figs Ij,2f, 3f). Stroke volumes for both diastoleand systole were then calculated by integratingthe area under the volumetric flowrate curve versus time. The mean of theabsolute value of these two measurementswas the aqueductal CSF stroke volume.RESULTSThe routine MR images obtained inall patients displayed ventriculomegaly,usually out of proportion tosulcal enlargement (although varyingdegrees of atrophy were also present).Age, sex, aqueductal CSF flow voidscore, aqueductal CSF stroke volume,and response to shunting are summarizedin Table 1.All 12 patients in this series withstroke volumes greater than 42 p.Lresponded to shunting (Fig 1), whilehalf of the six patients with an aqueductalCSF stroke volume of 42 iL orless did not respond (Figs 2, 3). Patientswith an aqueductal CSF strokevolume greater than 42 p1 were,therefore, considered to have hyperdynamicCSF flow and positive CSFflow study findings, while those withVolume 198 #{149} Number 2 Radiology #{149} 525
Page 1: NeuroradlologyWilliam C. Bradley, J
Page 5 and 6: a. b. c.d. e. f.Figure 3. Images an
Page 7: 6. Laws ER, Mokri B. Occult hydroce

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