CT图像质量的影响因素及高分辨率CT图像扫描参数的选择

目的获得适当的高分辨扫描条件并与普通扫描进行对比。方法用随机带来的水模进行扫描，计算出空间分辨率和密度分辨率。结果影响ＣＴ图像质量的因素很多，对于高档机（ＰＱ２０００），选择高分辨率扫描条件（小焦点、锐利卷积函数、１３０ｋＶ、４００ｍＡｓ、２ｍｍ层厚）可得到２０个线对的空间分辨率，由于选择大ｍＡｓ，可使密度分辨率的下降得到一定补偿。此外，扫描后用平滑卷积函数重建可使密度分辨率提高到３．９ｍｍ。对于中低档机（ＩＱＸＴＲＡ），高分辨率扫描条件的应用反而使空间分辨率和密度分辨率下降。结论对于中低档机应由工程师进行技术参数的测量，来决定能否进行高分辨率扫描。     

64层螺旋CT肺部高分辨率图像质量影响因素的体模研究

目的 分析影响肺部高分辨率CT(HRCT)图像质量的主要因素,探讨常规肺部容积扫描条件下获得HRCT图像质量的可行性.方法 应用64层CT对Catphan500模具进行连续、重复扫描.对比内容:扫描方式(轴面扫描、螺旋扫描)、kV值(140、120 kV)、层厚(1.25、5.00 mm,其中5.00 mm图像折分为1.25 mm)、重建算法(骨+算法、肺算法).评价内容:空间分辨率、密度分辨率、图像噪声.统计分析采用析因设计方差分析.结果 扫描方式在密度分辨率(轴面扫描:11.44±0.04;螺旋扫描:12.61±0.04)、图像噪声(轴面扫描:5.89±0.05;螺旋扫描:6.92±0.05)上差异均有统计学意义(F值分别为539.61、179.02,P值均＜0.01),轴面扫描密度分辨率高于螺旋扫描,图像噪声低于螺旋扫描;重建算法间在空间分辨率(骨+:9.90±0.09;肺:7.40±0.09)、密度分辨率(骨+:11.39±0.04;肺:12.65±0.04)、图像噪声(骨+:6.55±0.05;肺:6.28±0.05)上差异均具有统计学意义(F值分别为375.00、627.95、13.97,P值均＜0.05),骨+算法优于肺算法但噪声值略高.结论 容积扫描在密度分辨率、图像噪声控制上较传统HRCT稍差,但在空间分辨率上容积扫描骨+算法重建与HRCT图像质量相当,用于显示肺内细节时容积高分辨率CT可代替常规HRCT.     

Dose and image quality of electron-beam CT compared with spiral CT.

RATIONALE AND OBJECTIVES: To examine dose and image quality of electron-beam CT (EBCT) with continuous volume scan versus spiral CT. METHODS: An EBCT scanner was compared with a spiral CT (SCT) scanner. Three phantoms were used to measure low-contrast resolution, high-contrast resolution, slice width, and dose. RESULTS: The EBCT scans showed 30% lower high-contrast resolution for most settings. The dose was comparable to that of spiral CT with 3 mm collimation and 76%/106% higher with EBCT for 1.5 mm/6 mm collimation. Low-contrast resolution was comparable to that of spiral CT using 3 mm collimation, slightly worse for 1.5 mm, and bad for 6 mm EBCT collimation (four times higher dose to reach comparable contrast-to-noise ratio). CONCLUSIONS: Significant restrictions were found using EBCT with continuous volume scan. The authors found that 3 mm collimation can yield acceptable high-contrast resolution and good low-contrast resolution compared with spiral CT. The use of 6 mm or 1.5 mm collimation needs to be restricted to selected cases.     

胸部能谱成像模式与常规CT扫描的辐射剂量及图像质量的仿真体模研究

目的 通过仿真胸部体模研究胸部能谱CT不同方案成像模式与常规胸部CT扫描的辐射剂量、图像质量、对比噪声比及主观评分对比,获得最佳能谱扫描参数。方法 对仿真胸部体模分别进行常规胸部CT扫描以及3种不同扫描方式的能谱CT成像。3种能谱模式为宝石能谱CT （GSI）Assist模式（方案A）、管电流平均值时的GSI模式（方案B）及管电流最大值时的GSI模式（方案C）。所有扫描方式分别在噪声指数（NI）=9和11时,螺距0.984∶1,依次扫描。记录辐射剂量,同时测量感兴趣区（ROIs）5个不同层面水平的脂肪和肌肉组织的图像噪声值（SD）以评价图像质量。所有扫描序列由两位资深放射医师对肺窗肺纹理及分支5分制主观评分。结果 NI=9和11时,常规CT平扫与方案A、B、C的有效剂量（E）值分别为（8.0、8.5、6.2、10.4）和（5.3、5.1、4.3、6.2）mSv。NI=9时,常规胸部CT平扫与方案A、C的SD值差异有统计学意义（F=4.496,P<0.05）;NI=11时,方案A、B、C与常规胸部CT平扫SD值差异有统计学意义（F=8.425,P<0.05）;常规胸部CT扫描中,NI分别为9和11时SD值差异有统计学意义（t=－2.570,P<0.05）;在相同能谱扫描模式中,NI不同,SD值差异均无统计学意义（P>0.05）。NI相同扫描模式不同及扫描模式相同NI不同时,CNR及主观评分差异均无统计学意义（P>0.05）。结论 合理的能谱扫描模式与常规扫描的辐射剂量没有明显差异,但能谱扫描模式可以获得较高的图像质量。此外,选择合适的噪声指数在图像质量相仿的同时可以明显降低辐射剂量。综合辐射剂量及图像质量,能谱CT智能模式可以达到辐射剂量及图像质量的双向平衡。     

Accounting for patient size in the optimization of dose and image quality of pelvis cone beam CT protocols on the Varian OBI system

Objective:

The purpose of this study was to develop size-based radiotherapy kilovoltage cone beam CT (CBCT) protocols for the pelvis.

Methods:

Image noise was measured in an elliptical phantom of varying size for a range of exposure factors. Based on a previously defined “small pelvis” reference patient and CBCT protocol, appropriate exposure factors for small, medium, large and extra-large patients were derived which approximate the image noise behaviour observed on a Philips CT scanner (Philips Medical Systems, Best, Netherlands) with automatic exposure control (AEC). Selection criteria, based on maximum tube current–time product per rotation selected during the radiotherapy treatment planning scan, were derived based on an audit of patient size.

Results:

It has been demonstrated that 110 kVp yields acceptable image noise for reduced patient dose in pelvic CBCT scans of small, medium and large patients, when compared with manufacturer''s default settings (125 kVp). Conversely, extra-large patients require increased exposure factors to give acceptable images. 57% of patients in the local population now receive much lower radiation doses, whereas 13% require higher doses (but now yield acceptable images).

Conclusion:

The implementation of size-based exposure protocols has significantly reduced radiation dose to the majority of patients with no negative impact on image quality. Increased doses are required on the largest patients to give adequate image quality.

Advances in knowledge:

The development of size-based CBCT protocols that use the planning CT scan (with AEC) to determine which protocol is appropriate ensures adequate image quality whilst minimizing patient radiation dose.     

双定位像结合Care Dose 4D和Care kV技术在降低肺部CT辐射剂量的临床应用价值

目的 探讨双定位像结合Care Dose 4D和Care kV技术在肺部CT检查中的可行性及其临床应用价值。方法 连续纳入临床确诊为肺部肿瘤行肺部CT扫描的患者60例,按随机数表法分为对照组和试验组,每组各30例,对照组行单定位像（AP）结合Care Dose 4D和Care kV技术扫描,试验组行双定位像（AP和lat）结合Care Dose 4D和Care kV技术扫描。由2位高年资医师采用双盲法对两组图像和病变组织的信噪比（SNR）、对比噪声比（CNR）,及整体图像质量进行综合分析和评价,同时计算有效辐射剂量。结果 60例患者均成功完成肺部CT检查,试验组整体图像质量评分为4.57±0.45,与对照组的4.73±0.45相比差异无统计学意义（P>0.05）。对照组图像SNR、CNR、病变组织SNR、CNR与试验组相比差异均无统计学意义（P>0.05）。试验组和对照组的容积CT剂量指数CTDI_vol、剂量长度乘积（DLP）、有效剂量（E）,差异有统计学意义（t=8.514、8.464、8.464,P<0.001）。与对照组相比,试验组有效剂量降低了33.3%。结论 较单定位像（AP）肺部CT检查,双定位像（AP和lat）结合Care Dose 4D和Care kV技术肺部CT检查可获得满足诊断及临床需求图像,同时明显降低辐射剂量,可成为肺部CT常规检查方式。     

CT机质量控制检测的探讨

目的:CT机质量控制检测方法的探讨及应用。方法:用美国模体实验室的Catphan 500模体和瑞典奥利科公司的Solidose 400剂量仪检测CT机扫描架的定位光精度、扫描床运动精度、层厚、CT值线性、视野均匀性、噪声、高对比度分辨率、低对比度分辨率和CT剂量指数(CTDI)。结果:所检测CT机作为整机均合格,但部分指标不合格。结论:通过对噪声、CT线性、对比度分辨率等图像性能参数的检测,可有效保证系统性能良好和维持最优化的图像质量;对CTDI的检测,可及时了解辐射危险水平,进而优化扫描方案,在保证诊断的前提下降低病人受照剂量。     

低剂量高分辨CT对观察肺间质病变图像质量的影响

目的观察肺间质病变不同剂量扫描的高分辨CT图像,分析其对图像质量的影响。方法对92例肺间质病变的患者接受胸部高分辨CT扫描,分别进行常规剂量（A剂量组,管电压140kV,管电流250mAs）和低剂量（B剂量组,管电压140kV,管电流150mAs）;超低剂量（c剂量组,管电压140kV,管电流75mAs）扫描。采用盲法对图像质量分别进行主观评价和客观评价,其中主观评价采用图像诊断接受率评分和主观噪声评分法进行评分,以肺窗和纵隔窗分别进行观察,采用5分制,并用Kappa检验评价观察者的一致性;图像质量客观评价指标包括CT值和噪声值,ROI取左心室、背部竖脊肌和胸椎锥体中央,面积1．0cm2,测量其CT值和噪声值,层面设定为左心室层面。三组均采用同一层面。窗宽400HU、窗位40HU。结果两名医师在诊断接受率和图像噪声评估分值方面有很好的一致性（Kappa值分别为0．73和0．76）。三组剂量在图像诊断接受率评分及主观噪声评分方便差异有统计学意义（P〈d0．05）。而对于客观测量的左心室、背部竖脊肌、椎体的CT值,3组差异均无统计学意义（P均〉O．05）;对于噪声值,3组差异均有统计学意义（P均d0．05）。结论随着高分辨CT扫描剂量减低,图像质量逐渐降低,但在获得稳定图像质量的前提下,采取适当的低剂量高分辨CT扫描即可保证图像质量,又不影响临床诊断分析。而不论剂量大小,CT值的变化不明显。     

SR-NLM: A sinogram restoration induced non-local means image filtering for low-dose computed tomography

Radiation dose has raised significant concerns to patients and operators in modern X-ray computed tomography (CT) examinations. A simple and cost-effective means to perform a low-dose CT scan is to lower the milliampere-seconds (mAs) as low as reasonably achievable in data acquisition. However, the associated image quality with lower-mAs scans (or low-dose scans) will be unavoidably degraded due to the excessive data noise, if no adequate noise control is applied during image reconstruction. For image reconstruction with low-dose scans, sinogram restoration algorithms based on modeling the noise properties of measurement can produce an image with noise-induced artifact suppression, but they often suffer noticeable resolution loss. As an alternative technique, the noise-reduction algorithms via edge-preserving image filtering can yield an image without noticeable resolution loss, but they often do not completely eliminate the noise-induced artifacts. With above observations, in this paper, we present a sinogram restoration induced non-local means (SR-NLM) image filtering algorithm to retain the CT image quality by fully considering the advantages of the sinogram restoration and image filtering algorithms in low-dose image reconstruction. Extensive experimental results show that the present SR-NLM algorithm outperforms the existing methods in terms of cross profile, noise reduction, contrast-to-ratio measure, noise-resolution tradeoff and receiver operating characteristic (ROC) curves.     

Dual-source cardiac computed tomography: image quality and dose considerations

Computed tomography (CT) imaging of the heart, most prominently coronary CT angiography, is currently subject to intense interest and is increasingly incorporated into clinical decision-making. In spite of tremendous progress in CT technology over the past decade, the limited temporal resolution has remained one of the most severe problems, especially for cardiac imaging. The novel design concept of dual-source CT (DSCT) allows for an effective scan time of 83 ms independent of heart rate. While large trials are still missing, initial studies have shown improved image quality, especially for visualizing the coronary arteries and detecting coronary artery stenoses. Further investigations have shown that routine beta blockade to lower the heart rate is not necessary to reliably achieve diagnostic image quality. Other applications that may particularly benefit from increased temporal resolution are the analysis of ventricular function and of the cardiac valves. Dose issues which are of interest for cardiac CT in general are discussed in some detail, including a quantitative analysis of dose values and three-dimensional dose distributions. Various strategies to lower radiation exposure are available today, and DSCT offers specific potential for this.     

低剂量螺旋CT扫描技术

降低受检者CT检查辐射剂量一直是业内关心的热点问题。本文从CT辐射剂量的表达方法,图像质量评价指标,影响辐射剂量的因素以及低剂量扫描方案的合理应用等方面,介绍了低剂量螺旋CT扫描技术的研究进展。     

Optimized contrast-enhanced CT protocols for diagnostic whole-body 18F-FDG PET/CT: technical aspects of single-phase versus multiphase CT imaging.

The purpose of this study was to compare various PET/CT examination protocols that use contrast-enhanced single-phase or contrast-enhanced multiphase CT scans under different breathing conditions. METHODS: Sixty patients with different malignant tumors were randomized into 4 different PET/CT protocols. Single-phase protocols included an intravenous contrast-enhanced (Ultravist 370; iodine at 370 mg/mL) single-phase whole-body CT scan (90 mL at 1.8 mL/min; delay, 90 s) during shallow breathing (protocol A) or during normal expiration (NormExp; protocol B). Multiphase protocols included 2 separate CT scans in the arterial contrast enhancement phase (90 mL at 2.5-2.8 mL/min; bolus tracking; scan range, base of the skull to the kidneys) and the portal-venous contrast enhancement phase (delay, 90 s; scan range, base of the lungs to the proximal thighs) during shallow breathing (protocol C) or during NormExp (protocol D) followed by a low-dose CT scan during shallow breathing for attenuation correction and whole-body PET. Feasibility was assessed by comparing the misalignment of the upper abdominal organs quantitatively by means of the craniocaudal, lateral, and anterior-posterior differences on coregistered PET/CT images. For image quality, the occurrence of CT artifacts and mismatching of rigid body points were evaluated qualitatively. RESULTS: Misalignment was significantly lower for protocol B in almost all organs and represented the best coregistration quality. Surprisingly, protocol A showed significantly better alignment than the multiphase CT scans during NormExp. Misalignment values between the multiphase protocols were not significantly different, with a trend toward lower values for protocol D. The best CT image quality, with a significantly lower occurrence of artifacts, was found for protocols B and D (NormExp). The levels of mismatching of rigid body points because of patient movement in between the transmission and emission scans were similar for all protocols. CONCLUSION: Multiphase CT protocols presented a technical disadvantage represented by suboptimal image coregistration compared with single-phase protocols. Nevertheless, multiphase protocols are technically feasible and should be considered for patients who will benefit from a contrast-enhanced multiphase CT examination for diagnosis.     

Dual energy head CT to maintain image quality while reducing dose in pediatric patients

AimThe aim of this study was to use dual energy CT technology to maintain or improve image quality in pediatric head CT while simultaneously reducing radiation dose.Materials and methodsIn this retrospective study, helical head CTs performed using a standard head CT protocol were compared to studies performed with a dual energy (DE) protocol. Objective comparison was performed by measuring regions of interest in 11 areas of the brain. Subjective rating for image quality using a Likert scale, was performed by three radiologists. Radiation doses were evaluated using CT dose index and dose length product.ResultsSignal-to-noise ratio was, for the most part, not significantly different between the DE and conventional scans. Contrast-to-noise ratio was slightly lower for children over 6 year of age utilizing the dual energy protocol versus the standard protocol.Qualitatively, there was little difference in image quality in patients <6 years old, with the only significant difference in infratentorial noise. However, in patients >6 years of age, infratentorial noise, sharpness and diagnostic acceptability, as well as supratentorial sharpness were all significantly improved by DE CT technique. Radiation exposure as measured by CTDI and DLP was modestly lower with the dual energy protocol in all study populations.ConclusionDual energy CT can be used clinically in pediatric patients to maintain or improve image quality while reducing radiation dose.     

Rapid imaging protocol in trauma: a whole-body dual-source CT scan

The purpose of this study is to determine whether a single acquisition whole-body trauma multi-detector CT scan is able to reduce resuscitation time, scan time, and effective radiation dose without compromising diagnostic quality in the setting of polytrauma. Retrospective analysis of 33 trauma patients undergoing single acquisition whole-body CT with injury severity scores of ≥16 was compared to 34 patients imaged with a segmented whole-body CT protocol. Time spent in the emergency department, effective radiation dose, image quality, and mortality rates were compared. The single acquisition group spent 53.7 % less time in the emergency department prior to imaging (p?=?0.0044) and decreased scanning time by 25 %. The protocol yielded a 24.5 % reduction in mean effective radiation dose (24.66 mSv vs. 32.67 mSv, p?<?0.0001). The image noise was similar in both groups. Standardized mortality ratios were comparable. The single acquisition protocol significantly reduces time spent in the emergency department by allowing faster imaging at a lower radiation dose while maintaining image quality. Other contributors to reduction in radiation dose include use of dual-source CT technology, removal of delayed CT intravenous pyelogram, and arm positioning.     

Impact of image noise levels, scout scan dose and lens shield on image quality and radiation exposure in z-axis dose-modulated neck MSCT on 16- and 64-slice Toshiba Aquilion scanners

Objective

Assessing the impact of image noise (IN) levels, scout scan dose and lens shield use on image quality and radiation exposure in neck multislice CT (MSCT) when using z-axis dose modulation (DM).

Methods

Neck MSCT phantom studies with/without z-axis DM were performed by using different IN levels (S.D. 7.5-30 HU) and scout scan tube currents (7.5-50 mA) on Toshiba Aquilion scanners (16-/64-slice). Image quality indices were evaluated by two radiologists and radiation exposure parameters calculated. Cadaveric phantom measurements elucidated lens shield interactions with DM efficacy. The lowest dose scan protocol with diagnostic image quality was introduced into the clinical imaging routine and retrospectively evaluated in 20 age-matched patients undergoing neck MSCT with/without DM.

Results

The highest image noise level in DM neck studies with comparable image quality to standard neck CT amounted to 20 HU, resulting in a mean tube current of 50 mAs (CTDI_w 6.3 mGy). DM reduced effective dose by 35% and organ dose figures (lens, thyroid) by 33%. Scout scan dose lowering to 20 mA resulted in an effective dose (ED) decrease of 0.06 mSv (5%). Avoiding lens shield placement during scout scan effected an organ dose decrease of 20%. Overall contour sharpness and image contrast did not differ significantly (DM/without DM) whereas image noise was rated higher in DM neck CT studies (p < 0.05).

Conclusions

z-Axis dose modulation, as assessed on 16- and 64-slice Toshiba Aquilion scanners, is effective and mandatory in neck MSCT. DM efficacy can be enhanced by optimising scout scan doses and lens shield use.     

16层螺旋CT螺距对图像质量的影响

目的：研究16层螺旋CT的图像质量与螺距的关系。方法：在16层螺旋CT机上,选用轴扫、不同螺距扫描QA模型,测量分析相应图像的噪声、层厚响应曲线、高对比度空间分辨率及低对比度分辨率;观察MPR图像质量。结果：轴扫图像噪声为4.39±0.29,螺距为0.562、0.938、1.375及1.75时,分别为3.24±0.25、4.39±0.23、5.27±0.25及5.40±0.33。层厚响应曲线在轴扫中呈梯形,半高宽约为5mm;在螺旋扫描中呈铃形,半高宽也近似为5mm。高对比度空间分辨率都是0.8mm线径;低对比度分辨率都能看清1mm的小孔。螺距为0.562的MPR图像未见明显变形,螺距为0.938、1.375、1.75时有较明显的变形。结论：16层螺旋CT在螺距为0.938时扫描图像噪声与轴扫图像噪声近似;随着螺距的增大,图像噪声增大,层厚响应曲线半高宽相差不大,高对比度空间分辨率和低对比度分辨率不变,MPR重构图像质量变差。     

A method to obtain the same levels of CT image noise for patients of various sizes, to minimize radiation dose

The aim of this study was to develop a method of obtaining the same levels of CT image noise for patients of various sizes to minimize radiation dose. Two CT systems were evaluated regarding noise characteristics using phantoms and dosimetric measurements. Both CT systems performed well at dose levels used in normal clinical imaging, but only one was found to be suitable for low radiation dose applications. The CT system with the lowest noise level was used for further detailed studies. A simple strategy for manual selection of patient-specific scan parameters, considering patient size and required image quality, was implemented and verified on 11 volunteers. Images were obtained with at least the prescribed image quality at significantly reduced radiation dose levels compared with standard scan parameters. Depending on the diameter of the tomographic section, i.e. size of the subject, the dose levels could be reduced to 1-45% of the radiation dose with standard scan parameters (120 kV, 250 mAs, 10 mm). The results indicate a general potential for dose reduction in CT for slim patients. For tissue volume determination, large dose reductions can be achieved by adjusting the scan parameters for each individual. The concept of patient-specific scan parameters could be fully automated in the CT system design, but would require the scan to be specified in terms of image quality rather than X-ray tube load.     

Virtual computed tomography colonoscopy: artifacts, image quality and radiation dose load in a cadaver study

The purpose of our study was to evaluate the interdependency of spatial resolution, image reconstruction artifacts, and radiation doses in virtual CT colonoscopy by comparing various CT scanning protocols. A pig's colon with several artificial polypoid lesions was imaged after air insufflation with helical CT scanning using 1-, 3-, and 5-mm collimation, and pitch values varying from 1.0 to 3.0. Virtual endoscopic images and “fly through” sequences were calculated on a Sun Sparc 20 workstation (Navigator Software, GE Medical Systems, Milwaukee, Wis.). Several reconstruction artifacts as well as overall image quality were evaluated by three independent reviewers. In addition, radiation doses for the different CT protocols were measured as multiple-scan average dose using a 10-cm ion chamber and a standard Plexiglass body phantom. Generally, image quality and reconstruction artifacts were less affected by pitch values than by beam collimation. Thus, narrow beam collimation at higher pitch values (e. g. 3 mm/2.0) seems to be a reasonable compromise between quality of virtual endoscopic images and radiation dose load. Received: 4 February 1999; Revised: 16 June 1999; Accepted: 17 June 1999     

多层螺旋CT膝关节低剂量扫描对影像质量的影响

目的:探讨多层螺旋CT低剂量膝关节扫描的可行性及其对图像质量的影响。方法:收集2009年5月~10月,100例行膝关节CT扫描者根据扫描的管电压高低分为2组(其他扫描条件不变),每组50例,A组110kV和B组80kV(管电压选择110kV和80kV是依据分别观察10例在此条件下扫描的患者图像,应用80kV而不影响诊断)。测量膝关节髌骨上缘水平后方肌肉软组织固定ROI的CT值,以CT值的标准差(SD)作为图像噪声。通过CT机自动得到平均容积CT剂量指数(CTDIvol),再计算出剂量长度乘积(DLP)。获得的图像通过双盲法进行质量评分,对两组CTDIvol值、DLP值、图像噪声、及图像质量评分均值用t检验进行比较。结果:A组和B组的CTDIvol值分别为(5.29±0.23)和(2.08±0.15)mGy,DLP值分别为(61.26±11.64)和(24.21±4.64)mGy.cm,B组较A组下降约(60.68)%,两者之间差异均有统计学意义(t值分别为(82.4)和(20.91),P0.01,B组噪声均值略高于A组(分别为12.22±2.97和16.55±2.96),t=-7.299,P=0.000,但两组图像质量平均评分分别为(4.86±0.40)分和(4.82±0.44)分,差异无统计学意义(t=0.475,P0.05)。结论:16层螺旋CT应用低kV设置(80kV)扫描膝关节可大幅度降低辐射剂量且所得图像质量不影响诊断。     

Sensitivity, resolution and image quality with a multi-head SPECT camera.

This investigation sought to determine which collimation factors were most important in providing superior image quality with a three-headed SPECT device. The relationship between sensitivity, resolution and SPECT image quality was studied. Two different sets of parallel-hole collimators were used. The ultrahigh-resolution collimators have higher spatial resolution (8.9 versus 11.0 mm), but only 55% of the sensitivity of the high-resolution collimators. A phantom with hot rods was imaged with both collimator sets. Observers compared images with the ultrahigh-resolution collimators to images of varying counts with the high-resolution collimators and determined which high-resolution images matched the ultrahigh-resolution images in image quality. Eleven patient studies were acquired with both collimator sets for equal time, and observers chose which image set they preferred. Transverse images of brain and liver studies were simulated with varying resolution and counts and subjectively compared. The phantom study indicated that the improvement in resolution led to image quality comparable to increasing the number of counts by a factor of 2.5 to 3.4. The clinical studies showed that the ultrahigh-resolution collimators were preferred in a large majority of the cases. These trends were also seen in the simulation study. These results confirm that higher resolution collimators should be used with multihead SPECT devices. The improvement in resolution more than compensates for the loss in sensitivity, leading to an overall improvement in image quality.