new applications with the assistance of innovative ... · pdf filein spiral ct affecting all...

electromedica 68 (2000) no. 294

IntroductionSince its clinical introduction in 1991, volumetric CT

scanning using spiral or helical scanners has resulted ina revolution for diagnostic imaging. In addition to newapplications for CT, such as CT angiography and the assessment of patients with renal colic, many routine applications such as the detection of lung and liver lesions have substantially improved. Helical CT has improved over the past eight years with faster gantry rotation, more powerful x-ray tubes, and improved interpolation algorithms [1, 2]. However, in practice the spiral data sets from monoslice systems suffered from a considerable mismatch between the transverse (in plane) and the longitudinal (axial) spatial resolution. Inother words the isotropic 3-dimensional voxel could notbe realized apart from some very specialized cases [3]. Similarly, in routine practice a number of limitationsstill remained which prevented the scanning protocolfrom being fully adapted to the diagnostic needs [4].

The introduction of subsecond spiral scanning withthe SOMATOM Plus 4 at the RSNA 1994 was a firststep to facilitate routine clinical work with respect toscannable volumes, total scan time and axial resolution[5]. Compared the 1 sec scanners which were standardat that time, the 750 ms rotation time allowed one to scan33% longer volumes or to correspondingly reduce thetotal scan time or to correspondingly improve axial resolution.

The latest advance has been the recent introductionof multislice CT (MSCT) scanners. At the RSNA 1998,this new technology was introduced by several manu-facturers representing an obvious quantum leap in clini-cal performance [6-8]. Currently capable of acquiringfour channels of helical data simultaneously, MSCTscanners have achieved the greatest incremental gain inscan speed since the development of helical CT and have profound implications for clinical CT scanning.

Fundamental advantages of MSCT include substan-tially shorter acquisition times, retrospective creation ofthinner or thicker sections from the same raw data, and

improved three-dimensional rendering with diminishedhelical artifacts [9].

For example, the SOMATOM® Volume Zoom with a500 ms rotation time and the simultaneous acquisitionof 4 slices offers an 8-fold increase of performancecompared to previous 1s, single-slice scanning.

Obviously, such a quantum leap opens up a new areain spiral CT affecting all existing applications and allowing the realization of new clinical applications.The key issue is correspondingly increased volume coverage per unit time at high axial resolution and a correspondingly improved temporal resolution [6].

In general terms, the capabilities of spiral CT can beexpanded in various ways: to scan anatomical volumeswith standard techniques at significantly reduced scantimes; or to scan larger volumes previously not acces-sible in practical scan times; or to scan anatomical volumes with high axial resolution (narrow collimation)to closely approach the isotropic voxel of high-qualitydata sets for excellent 3-dimensional postprocessingand diagnosis.

Basic Principles

For discussion of spiral imaging the following defi-nition of pitch is commonly used:

Table travel per rotationP =

Collimation of single slice

With this definition the present standard range 1 ≤ p ≤ 2 for single slice systems is extended to 1 ≤ p ≤ 8. In Fig. 1 various sampling patterns of a 4-slicespiral are shown for representative values of the pitch.In this schematic view the projections are symbolizedby single arrows, which for simplicity are drawn in parallel.

From those examples we can draw the following conclusions:

Multislice Computed Tomography:Basic Principles and Clinical ApplicationsA. F. Kopp1, K. Klingenbeck-Regn2, M. Heuschmid1, A. Küttner1, B. Ohnesorge2, T. Flohr2, S. Schaller2, C. D. Claussen1

1Eberhard-Karls-University Tübingen, Department of Diagnostic Radiology, Tübingen, Germany2Siemens AG, Medical Engineering Group, Forchheim, Germany

New Applications with the Assistance of Innovative Technologies

electromedica 68 (2000) no. 2 95

1. For pitch values smaller than 4 the four slices over-lap to a certain degree after one rotation. Pitch 2 is atransparent case with double sampling. Therefore in thisregime 1 ≤ p ≤ 4 the multiple sampling can be used toreduce the tube current for a desired image noise and fora desired patient dose, respectively.

2. However, collecting data from multiple rotationsdegrades the temporal resolution of the system. There-fore for imaging of moving organs with high image quality, a pitch smaller than 4 should be avoided.

3. The distance between neighboring samples varieswith pitch periodically. Consequently, 180° LI and 360°LI spiral interpolators would yield a corresponding non-monotonic dependence of slice width on pitch and aretherefore not useful for practical purposes.

4. The distance between neighboring samples neverexceeds the slice collimation up to a pitch of 8. Thisopens up the possibility to realize a slice width inde-pendent of pitch up to a pitch of 8 and to completely eliminate broadening of the slice width.

Design Considerations for MSCTIt is easy to design a multi-slice scanner for a fixed

slice collimation, the challenge is to design the detectorin such a way as to meet the clinical requirement of different slice collimations adjustable to the diagnosticneeds. There are basically two different approaches, thematrix detector with elements of a fixed size or the adaptive array principle. Both principles will be brieflydescribed and compared.

An example of a matrix detector is sketched in Fig. 2. In axial direction the detector is divided into 16small elements each providing a 1 mm thick slice at the

center of rotation [10]. The outer detector rows cannotbe used individually. In the example of Fig. 2 the 1 mmslice is smeared over about 6 mm. The only way out is to sum the signals of the outer rows to generate thickslices. However, the unnecessary mechanical cuts and

Figure 2Fixed Array Detector. The slice width is compared to thesmearing of the slice caused by the cone-angle.

It is shown that for the exampleof a 16-row detector, the outer-most slice of nominal thickness

1.0 mm is broadened to 6.6 mmby smearing (right half of figure).The problem can be overcome by combining several slices to awider slice (left half of figure).

Then, however, separators between the slices are not neededfor the outer slices.

sw: 4.0 mm

4.7 mm 6.6 mm

FOV

sw: 1.0 mm

16 detector rows

z

Figure 1Sampling Patterns of a 4-slicespiral scan at different pitch values. At pitch 1 and 2, each z-position is sampled 4 and 2 times respectively.

The spacing between samplesdecreases from d to d/2 whengoing from pitch 1 to pitch 1.5,then increases again to d whenincreasing the pitch to 2.

At a pitch of 4, each sample isacquired once and the samplingdistance is d (d denotes the slicecollimation).

Pitch 1 Pitch 2

Rot. 1

Rot. 2

Rot. 3

Rot. 4

Rot. 1

Rot. 2

Rot. 3

Rot. 4

Rot. 1

Rot. 2

Rot. 3

Rot. 1

Rot. 2

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Pitch 1.5 Pitch 4


optical separations between the small elements, corres-pondingly reduce the geometrical efficiency and there-fore the dose efficiency of the system. In summary, the matrix detector is well suited to scan at 4 x 1 mmcollimation but not more than 4. Wider collimations 4 x 2 mm, etc. can be realized by signal combination during read out but at the expense of dead zones and acorresponding waste of dose. These arguments lead tothe development of the Adaptive Array Detector [9].

The design of the Adaptive Array Detector (AAD) takes into account the cone beam constraints for optimalimage quality, optimizes the dose efficiency and in conjunction with an Adapted Axial Interpolator (AAI)provides a flexible selection of slice widths [6, 11, 12].The design principle is depicted in Fig. 3. Narrow detector elements are close to the center; the width of the detector rows increases with distance from thecenter. Unnecessary dead spaces are avoided and with the corresponding prepatient collimator and the proper read-out schemes the following combinations of collimation can be achieved: 2 x 0.5 mm, 4 x 1 mm, 4 x 2.5 mm, 4 x 5 mm, 2 x 8 mm and 2 x 10 mm (Fig. 4).These combinations represent the collimation of the X-ray beam at center: e. g. a 4 x 5 mm collimation means a X-ray beam width at center of 20 mm. Conse-quently with sequential imaging four 5 mm slices wouldbe generated during one rotation.

In spiral imaging the variety of axial sampling patterns as a function of pitch allows both: obtaining slice widths independent of pitch and reconstructing amultiplicity of slice widths from a scan with collimationnarrower than s. To achieve this the AAI-scheme pro-vides a set of linear and nonlinear interpolators whichare adapted to the desired pitch, collimation and slicewidth. To give some examples: from a spiral scan with4 x 1 mm collimation slice widths of 1, 1.25, 1.5, 2.0,2.5, 3.0, 4.0, 5.0 up to 10 mm can be obtained by adjust-ing the width and the functional form of the inter-polator. On the other hand, a selected slice width s, like s = 5 mm, may be obtained from different collimator settings, like 4 x 1 mm or 4 x 2.5 mm. This is importantto remember for clinical applications, as the narrowercollimation is preferable for image quality reasons, i. e.the reduction of partial volume effects [9].

Yet another design criterion should be emphasized:spiral scanning at large pitch, e. g. large table velocity,implies a more severe inconsistency between direct projections and the complementary projections, takenhalf a rotation later with a quarter detector offset. Thereason is changing anatomy in axial direction, which isparticularly pronounced for large pitch applications, i. e.rapid table movement. Consequently, image quality athigh spatial resolution and large pitch is becoming more dependent on the flying spot technology whichprovides a quasi-instant doubling of the in plane samp-ling rate.


Figure 3Design of the Adaptive ArrayDetector. The physical width ofthe detector is approximately 40 mm. Slice widths at the axisof rotation range from 1 mm forthe inner slices to 5 mm for theouter slices.

Figure 4Available Collimations and read-out schemes for the AdaptiveArray Detector (AAD). The dotted bar indicates the collima-tion at the detector.

Prepatient collimation is adjustedcorrespondingly.

z

1 1.5 2.5

5

in mm

Magnification center to detectorby a factor of approximately 2

appr. 40 mm

2 x 0.5 mm

4 x 1.0 mm

4 x 2.5 mm

2 x 8.0 mm

4 x 5.0 mm


In conclusion, image quality in multi-slice spiralscanning must be optimized with respect to several factors [13]:

1. The narrowest collimation, consistent with the coverage of a certain volume and with a certain scan time, to minimize partial volume effects and to optimizeimage quality.

2. Fastest rotation time to maximize z-coverage andto minimize motion blurring.

3. Pitch greater than 4 to preserve temporal resolu-tion and to minimize motion blurring.

4. The exploitation of flying focal spot technology toavoid artifacts at high spatial resolution.

To measure section profiles of multi-spiral scanninga thin gold plate (thickness 50 µm) in air has been aligned orthogonal to the scanner axis and has beenscanned in spiral mode. Some of the resulting slice sen-sitivity profiles (SSP) are shown in Fig. 5 for a 4 x 1 mmcollimation, a slice width of 2 mm and different pitch

values. Obviously the AAI indeed results in slice widthsindependent of pitch; but even more important, thefunctional form of the SSPs is also identical andpractically independent of pitch. Slice broadening andlong-range tails of the SSP, which prohibited the use of fast table speeds in single slice spiral scanning, can becompletely avoided. From this perspective the wholerange up to a pitch of 8 can be used for practical pur-poses in multi-slice scanning [6].

The second new and attractive feature of the multi-spiral AAI is illustrated in Fig. 6. From a scan with 4 x 1 mm collimation SSPs with different width can beobtained: 1.25 mm, 2.0 mm and 4.0 mm respectively.Excellent agreement between theory and measurementis observed. This feature is the basis of Combi Scans.This provides considerable flexibility in image recon-struction [14] especially for imaging of the base of theskull and lung (Fig. 7).

Anatomical structures that generate spiral artifactsare well known from single slice spirals. The most difficult situations arise from bony structures (high

Figure 5Slice Sensitivity Profiles, Collimation 4 x 1 mm, slicewidth 2 mm, different pitch values.

Figure 6Slice Sensitivity Profiles, Collimation 4 x 1 mm, pitch 3,different slice widths.

Pitch 3

Measured: -FWHM = 2.05 mm

Pitch 5

FWHM = 2.1 mm

Pitch 7

FWHM = 2.1 mm

: calculated : measured z [SW]

Measured: -FWHM = 1.35 mm FWHM = 2.05 mm FWHM = 4.0 mm

: calculated : measured

1

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-4 -2 0 2 4 -4 -2 0 2 4 -4 -2 0 2 4

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Figure 7Combi Scan: lung study with 4 x 1 mm collimation, pitch 6.Reconstruction of 5 mm imagesfor soft tissue (a) and standardlung window (b);

1.25 mm high resolution images for detection of interstitial disease (c). HR-MPR (d) clearly depicts segmental anatomy.

a b

c d


contrast) which are strongly inhomogeneous in axial direction. A demanding example is the base of the skullwith bony structures abruptly ending in an image plane.Phantom studies have shown that a larger pitch and narrower collimation is much more favorable for suppressing artifacts than a lower pitch and wider colli-mation for equal z-coverage. The underlying reason is the better elimination of partial volume artifacts.From image quality reasons, only, the strength of multi-slice spiral scanning is the ability to cover anatomicalvolumes with narrowest collimation and thereby to minimize partial volume effects. This is only a matter ofscanning technique (collimation) and is independent of the selected slice width. For optimization of image quality we derive the rule: the narrowest collimationshould be selected which is consistent with volume coverage and scan time. This generally results in largepitch values (e. g. from 4 to 6) which are also helpful toavoid motion blurring [13].

Clinical ApplicationsThe advantages of MSCT are important to many

applications of CT scanning, including survey exams inoncologic or trauma patients and the characterization offocal lung and liver lesions through the creation of thinsections retrospectively. However, the greatest impacthas been on CT angiography, cardiac imaging, virtualendoscopy, and high resolution imaging [15].

CT Angiography

A fundamental advantage of a multislice scannerover monoslice systems is its ability to obtain a first circulation study of a rapidly injected contrast boluswith thinner images. Determining circulation time either by a preliminary minibolus or by online bolustracking software is important in matching the acqui-sition interval to the first-circulation time of the in-jected bolus. As a result of the shorter acquisition time,the contrast dose can be significantly reduced.

CT angiography of the intracranial vessels benefitsfrom the quick and detailed scanning technology ofMSCT. At 1 mm-collimation, the circle of Willis can bescanned within 10 seconds. This permits the entire scanto be completed during the first pass of iodinated con-trast material through the arterial system. The use ofMSCT with CT angiography demonstrates the spatialrelationship of an aneurysm with the feeding vessel, aswell as the shape of the aneurysm itself, because the same bolus can be followed continuously throughout itscourse. For CT angiography of the thoracoabdominalaorta a collimation of 2.5 mm, a pitch of 5-6 at a rota-tion speed of 0.5 s are used. Volume coverage is fromthe thoracic inlet to the inguinal region, a 50 to 55 cmarea that can be covered in an acquisition interval of approx. 20 s (Fig. 8). Reconstructions with 50% overlapare used, generating 400-450 images for the three-dimensional data set. A complete lower extremity study

Figure 8MSCTA of the thoracoabdominalaorta. Stanford Type B Dissection.MPRs from images with 3 mmslice-width and 1 mm increment.The spiral scan was acquiredwith 4 x 2.5 mm collimation,pitch 5, and 0.5 s rotation time.The total scan time for a spirallength of 550 mm was 22 s.Courtesy of Dr. Baum, Erlangen.

a


can be performed from the level of the renal vascular pedicles to the ankles. A 2.5 mm collimation, a pitch of6 and 50% overlap reconstructions are used (Fig. 9). A first-pass circulation study can be obtained withoutvenous overlay. The total number of images generated is 800 to 1000. With multislice CT operating at pitch 6and collimation of 4 x 1 mm, a CTA of the pulmonaryarteries can be acquired in less than 25 s. Image thick-ness of 1.25 mm significantly increases detectability ofsubsegmental emboli in comparison to monoslice spiralCT using 2 to 3 mm image thickness [16]. CTA of thevisceral branch vessels can be performed significantlyfaster and/or with increased spatial resolution. Using a

Figure 9Peripheral Runoffs. Spiral scanwith 4 x 2.5 mm collimation,pitch 6, 0.5 s rotation time.

The total scan time for a spirallength of 1000 mm was 34 s.

Left: MIP from images with 3 mm slice width, 2 mm increment.

Right: VRT from images with 6 mm slice width, 4 mm increment.

▲

a

b

Figure 10CTA (a, b) of visceral branchvessels (collimation 4 x 1 mm,pitch 5, 120 cc contrast).

On the VR images a stenosis inthe SMA (arrows) can be readilyappreciated which was confirmedat conventional angiography (c).

c



collimation of 1 mm allows for detection of even minorbranches (Fig. 10). The ability to cover the entire chestin10 s allows the scanning of children without sedation.This can be used to easily perform CTA of the largethoracic vessels before or after surgery of complex mal-formations [8].

Cardiac Imaging

Electron Beam CT scanning (EBCT) has been established as a non-invasive imaging modality for imaging coronary calcification. Major clinical appli-cations are the detection and quantification of coronarycalcium and non-invasive CT angiography (CTA) of thecoronary arteries [17]. Current limitations of EBCTimaging include the limited reproducibility of coronarycalcium quantification [18], the inability to detect non-calcified atherosclerotic plaques and the limited spatialresolution of 3D visualizations of the coronary arteries.Because of the restriction to axial, non-spiral scanningin ECG-synchronized cardiac investigations, acquisi-tion of 3D volume images by using EBCT can only provide limited z-resolution within a single breath-holdscan. Retrospectively ECG-gated single-slice spiralscanning does not allow for sufficient continuous volumecoverage within reasonable scan times. RetrospectivelyECG-gated multi-slice spiral scanning, however, has thepotential to completely cover the heart volume withoutgaps within one breath-hold [19]. Mechanical multi-slice CT systems with simultaneous acquisition of four slices, half-second scanner rotation and 125 ms maximum temporal resolution allows for considerablyfaster coverage of the heart volume, compared to single-slice scanning. This increased scan speed allows usingthinner collimated slice widths and thus to increasingthe z-resolution of high-resolution examinations such asCTA of the coronary arteries [20].

ECG-synchronized multi-slice spiral scans are acquired with heart rate dependent table feed (“pitch”)adaptation. Dedicated spiral algorithms provide 125 ms(60 ms as theoretical limit) temporal resolution and areoptimized with regard to volume coverage. This allowsreconstruction of overlapping images (increment < slice-width) at arbitrary z-positions and during any givenheart phase [21]. This reconstruction technique com-bines partial scan reconstruction and multi-slice spiralweighting in order to compensate for table movementand to provide a well-defined slice sensitivity profile[19].

For retrospectively ECG-gated reconstruction eachimage is reconstructed using a multi-slice partial scandata segment with an arbitrary temporal relation to theR-wave of the ECG-trace. Image reconstruction duringdifferent heart phases is feasible by shifting the startpoint of image reconstruction relative to the R-wave.For a given start position, a stack of images at differentz-positions covering a small sub-volume of the heart canbe reconstructed owing to mutlislice data acquisition.

Fig. 11 shows an example of how the cardiac volume is successively covered with stacks of axial images (shaded stacks) reconstructed in consecutive heart cycles. All image stacks are reconstructed at identicaltime-points during the cardiac cycle. At the same time,the 4 detector slices travel along the z-axis relative to thepatient table. In each stack, single-slice partial scan data segments are generated with equidistant spacing inthe z-direction depending on the selected image recon-struction increment [21]. Continuous volume coveragecan only be achieved, when the spiral pitch is adapted tothe heart rate in order to avoid gaps between imagestacks that are reconstructed using data from differentheart cycles. In order to achieve full volume coverage,the image stacks reconstructed in subsequent heart cycles must cover all z-positions. Thus, the pitch, whichcan be used for image acquisition is limited by the patient’s RR-interval time [19].

The cardiac multi-slice data acquisition on the SOMATOM Volume Zoom are performed using 500 msfull rotation time and 4 x 1 mm or 4 x 2.5 mm colli-mated slice width. Non-contrast enhanced spiral scansfor coronary calcium scoring are performed with 3 mmslice-width (SW = 3 mm, SWcoll = 2.5 mm) and 1 mmimage reconstruction. For CTA of the coronary arteriesand for functional heart imaging 2 different scan protocols with 3 mm slice-width and with 1.25 mm slice-width can be used (Fig. 12). For both protocols,non-ionic contrast material is intravenously injected ata flow rate of 3 ml/s. The delay times between start ofcontrast injection and scan start for optimal contrast enhancement is determined individually for each patientby injection of a 20 ml test bolus [20].

Figure 11Reconstruction with retro-spectively ECG-gated 4-slicespiral scanning.

Data ranges are selected withcertain phase relation to the RR-intervals. 3D volume imagesare generated from image stacksreconstructed in consecutiveheart cycles.

Slice q = 0Slice q = 1Slice q = 2Slice q = 3

ECG-Signal(~ 70 bpm)

t [sec] (0.5 sec/rotation)

161514131211109876543210

0 0.5 1 1.5 2 2.5 3 3.5


Figure 1249-year-old male with CHD of the RCA. S/P posterolateralmyocardial infarction 4 monthsago.

Patient underwent balloon angioplasty of subtotal stenosisat the beginning of the descend-ing part of the RCA.

Patient came in for follow-upperformed with both coronaryCT angiography (a) and conventional angiography (b).

Both conventional angiographyand CT angiography (3D Virtuoso®, Siemens) clearlyshow the patency of the RCA at the level of the ballon angio-plasty.

There is only minor residual stenosis of approx. 10-20% (arrows).

Scan: Siemens SOMATOM®

Volume Zoom; 140 kV, 300 mAs,collimation 4 x 1 mm; slice width 1.25 mm, increment 0.6 mm.

a

b

Figure 13Noninvasive CT coronary angiography: Volume renderedimage (3D Virtuoso®, Siemens)depicts three high grade stenoses(arrows) in the LAD and at theorigin of the diagonal branches.These findings are confirmed atconventional angiography.

a

b



14

15

The high spatial resolution, the absence of motion artifacts and the good overall image quality of the clinical MSCT images of the entire heart volume let appear multislice spiral CT as a promising modality forthe non-invasive evaluation of coronary calcification.The scan time needed to acquire continuous ECG-gatedmultislice spiral CT image data is significantly reducedcompared to EBCT (≈ factor 2.5) and single slice CT(≈ factor 5). Data with 3 mm slice width can be used forvolumetric coronary calcium scoring. This alternativescoring method has the potential to improve the repro-ducibility of repeat calcium scoring compared to theconventional Agatston-score. Phantom studies haveshown that non-overlapping sequential scanning is animportant contributor to the inter-scan variability ofAgatston- and volumetric Ca-scores due to partial volume errors in plaque registration [22]. ECG-gatedvolume coverage with multi-slice spiral CT and over-lapping image reconstruction, however, was found toimprove the reliability of coronary calcium quantifi-cation especially for small plaques. ECG-gated multi-slice spiral CT can potentially be of high value for coronary calcium evaluation especially for patients undergoing lipid-lowering statin therapy and for follow-up evaluations of patients after heart transplantation[23].

In contrast to sequential CT scanning z-resolution of ECG-gated spiral images with 3 mm slice-width can be improved by using overlapping reconstruction with 1 mm slice increment. Moreover, the fast scan speed allows covering the entire heart with 1.25 mm slices within a single breath-hold (10 cm in 25-35 s). 3D reconstruction with 1.25 mm slice-width and sub-millimeter image increment allows generating high-resolution visualizations of the coronary arteries, whichmay be suitable for a highly accurate diagnosis of coronary artery disease (Fig. 13, 14) [24]. Even moreimportant, the first results indicate that MSCTA not only allows non-invasive imaging of coronary plaquesbut also assessment of plaque composition (i. e., soft, fibrous, calcified) (Fig. 15). Thus, this new technologyholds promise to allow for the non-invasive imaging ofrupture-prone soft coronary lesions and may have theoption to lead to early onset of therapy [25].

High Resolution Imaging

Imaging of the temporal bone is a major challenge forclinical CT and a good example of the need for high resolution CT. Imaging of the temporal bone is improvedusing MSCT because the in-plane resolution can begreatly increased. The temporal bone is a structure ofhigh intrinsic contrast and is routinely scanned withthin collimation. Both the 2 x 0.5 mm and the 4 x 1 mm mode on the SOMATOM Volume Zoom are applicable(pitch 2 or 3.5) and the tube current can be reduced to below 200 mAs (Fig. 16). The reconstruction kernelsenable maximum spatial resolution up to 24 line pairs/

Figure 14Virtual angioscopy (bottom right) of circumflex branch ofleft coronary artery. VRT (left)and MPR (top right) images help navigating the virtual endoscope in the coronary artery (3D Virtuoso®, Siemens).

Figure 15MSCTA of LAD: Non-calcifiedsoft plaque (arrow) with densityof approx. 5 HU.

This lipid-core plaque was classified as prone to rupture inintracoronary ultrasound.

Scan: collimation 4 x 1 mm, pitch 1.5,300 mAs, 120 cc contrast.


Figure 16High resolution image of thetemporal bone.

Note the excellent definition of the ossicles at a collimationthickness of 0.5 mm (200 mAs, 120 kV).

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[9] Ohnesorge, B., Flohr, T., Schaller, S. et al: Technische Grund-lagen und Anwendungen der Mehrschicht-CT. Radiologe 1999; 39:923-31.

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[13] Flohr, T., Schaller, S., Ohnesorge, B., Klingenbeck-Regn, K.,Kopp, A. F.: Evaluation of Image Artifacts in Multislice CT. Radiology1999; 213 (P):317.

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[15] Berland, L. L., Smith, J. K.: Multidetector-array CT: once again,technology creates new opportunities. Radiology 1998; 209:327-9.

[16] Leung, A. W., Klein, J. S.: Optimization of spiral CT of the thorax. Radiology 1999; 213 (P):73.

[17] Achenbach, S., Moshage, W., Ropers, D., Nossen, J., Daniel, W. G.:Value of electron-beam computed tomography for the noninvasive detection of high-grade coronary-artery stenoses and occlusions.N.Engl.J.Med. 1998; 339:1964-71.

[18] Flamm, S. D.: Coronary Arterial Calcium Screening: Ready forPrime Time? Radiology 1998; 208:571-2.

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cm. At this resolution, the delicate structures of themiddle and inner ear are sharply delineated and evensubtle changes can be assessed. Another advantage ofusing MSCT to image the temporal bone is that the slice thickness is reduced to 1 mm or below, thus mini-mizing the partial volume effects and further increasingimage quality of subtle structures [26].

Impact on Radiological PracticeThe large number of images generated by MSCT is a

major issue for workstation performance, film display,and PACS archiving. The images should be reviewed in a cine paging format at a workstation for diagnosticpurposes [15]. Film hard copy will only be used for reference display. Planning for PACS must take into account this exponential growth in image data generatedby this new technology. Rapid generation of 3D data setsis important for inclusion in the diagnostic study inter-pretation and for demonstration to referring clinicians.The hundreds or thousands of thin sections acquiredusing MSCT are incompatible with traditional viewingpractice; thus MSCT will force a rapid transition of radiology from two-dimensional to volumetric imaging.



Author’s address:

Andreas F. Kopp, M.D.Eberhard-Karls-University TübingenDepartment of Diagnostic RadiologyD-72076 Tübingen/GermanyTel: +49-(0)-70 71-29-8 20 87Fax: +49-(0)-70 71-29-58 45e-mail: [email protected]

[21] Ohnesorge, B., Flohr, T., Becker, C., Kopp, A. F., Schoepf, U. J.,Baum, U., Knez, A., Klingenbeck-Regn, K., and Reiser, M. F.: CardiacImaging with ECG-Gated Multi-Slice Spiral CT – Initial Experience.Radiology 2000, in Press.

[22] Ohnesorge, B., Flohr, T., Becker, C. R., Kopp, A. F., Knez, A.:Comparison of EBCT and ECG-gated multislice spiral CT: a study of 3D Ca-scoring with phantom and patient data. Radiology 1999; 213 (P):402.

[23] Becker, C. R., Knez, A., Ohnesorge, B., Flohr, T., Schoepf, U. J.,Reiser, M.: Detection and quantification of coronary artery calcifica-tions with prospectively ECG triggered multirow conventional CT andelectron beam computed tomography: comparison of different methodsfor quantification of coronary artery calcifications. Radiology 1999;213 (P):351.

[24] Kopp, A. F., Georg, C., Schröder, S., Claussen, C. D.: CT-Angio-graphie der Herzkranzgefäße bei koronarer 3-Gefäß-Erkrankung. Fortschr.Röntgenstr. 2000; 172:M3-M4.

[25] Kopp, A. F., Ohnesorge, B., Flohr, T., Schroeder, S., Claussen, C. D.:Multidetector-row CT for the noninvasive detection of high-grade coronary artery stenoses and occlusions: first results. Radiology 1999;213 (P):435.

[26] Klingenbeck-Regn, K., Schaller, S., Flohr, T., Ohnesorge, B.,Kopp, A. F., Baum, U.: Subsecond multislice computed tomography: basics and applications. Eur.J.Radiol. 1999; 31:110-24.

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