Digital skeletal radiography: spatial resolution requirements for detection of subperiosteal resorption

Forty direct-magnification (2:1 enlargement) radiographs showing various severities of subperiosteal resorption and 40 normal studies were selected and digitized. Images were processed to produce varying resolution, from 1.42 to 11.4 Ip/mm, corresponding to pixel sizes ranging from 0.04 to 0.32 mm. The conventional and digitized images were evaluated by six radiologists giving their decision confidence on a graded scale. Receiver operating characteristic analyses were performed from these data to compare the digital images with the conventional films. The results show significant improvement in diagnostic accuracy as pixel size decreases to the level of 0.08 mm. Digital images with pixel sizes of 0.04 mm (11.4 Ip/mm) were not significantly different from the magnification radiographs in terms of observer performance. In conclusion, for high-resolution skeletal imaging as needed for detection of subperiosteal resorption, spatial resolution of 5.7 Ip/mm or less resulted in a significant loss of diagnostic accuracy, as compared with conventional films.     

Total digital radiology department: spatial resolution requirements

The minimum spatial resolution required for a total digital radiology department has yet to be defined. A pilot study designed to provide this information was performed. Abnormal and normal radiographic images of children were digitized and redisplayed on film at spatial resolutions of 5.0, 2.5, 1.25, and 0.625 lp/mm. These resolutions are comparable to a digital display of a 14 X 14 in. chest image having pixel elements of 4096 X 4096, 2048 X 2048, 1024 X 1024, and 512 X 512, respectively. Contrast resolution was maintained at 12 bits or 4096 gray levels. The three phases of data acquisition were (1) the standard analysis of receiver operating characteristics, (2) a checklist evaluation of the "seeability" of important structures, and (3) a comparison of all resolutions and a discernment of usability. Fifteen radiologists participated in the study. On the basis of the pediatric cases used, the results showed that the needed spatial resolution for a total digital radiology department may be around 2.5 lp/mm (2048 X 2048). Checklist data on seeability of structures and comparisons of all resolutions give information on specific changes that are occurring as the resolution is decreased, and, when included with the receiver-operating-characteristic data, they become a major component in developing a resolution standard. The finding that 2.5 lp/mm is the required spatial resolution makes construction of a total digital radiology department possible with present state-of-the-art technology.     

Nondisplaced fractures of the greater tuberosity of the humerus: sonographic detection.

In this retrospective study, the sonographic appearance of fracture of the greater tuberosity of the humerus was evaluated in 17 men and 14 women aged 20-69 years with acute, semiacute, or remote shoulder trauma in whom results of rotator cuff sonography had suggested the diagnosis of such a fracture. Clinical data, radiologic reports, sonograms, and initial plain radiographs of the shoulder were analyzed; clinical follow-up information was assessed in 22 patients. Sonography showed discontinuity and irregularity of the humeral cortex in all patients. In 25 patients (81%), displaced fracture fragments could be seen. Sonographic findings were suggestive of, but not specific for, fracture. Cortical abnormalities of the humerus were identified without modification of standard scanning protocols. A humeral fracture was confirmed with radiography in 24 patients; in 10 of them, the fracture had been missed initially on plain radiographs. It is concluded that, in evaluation of soft tissues in shoulder trauma, sonography may define rotator cuff abnormalities and occasionally help in detection of occult humeral fractures.     

ACR-NEMA digital imaging and communications standards: minimum requirements

The purposes, implications, and history of development of the American College of Radiology-National Electrical Manufacturers Association (ACR-NEMA) Digital Imaging and Communication Standard and its contents are briefly described, and the minimum requirements of the ACR-NEMA Digital Imaging and Communication Standard are described with a concise introduction of each layer. The usefulness, validity, current status, and future development of the standard are also discussed.     

Spatial resolution requirements for digital chest radiographs: an ROC study of observer performance in selected cases

Thirty-eight selected clinical radiographs were digitized and displayed on a 1,024-line monitor at pixel sizes of 1.6, 0.8, 0.4, and 0.2 mm. Eighteen experienced radiologists assessed the radiographs and digital images, which included 12 examples of abnormal solitary nodular density, ten examples of septal lines, and 16 controls, six of which showed diffuse lung abnormalities. For each level of spatial resolution and for film reading, observers gave their decision confidence on a sliding scale of probability. Receiver operating characteristic curves were generated from these data. It was found that while spatial resolution requirements for solitary nodules were not critical for pixel sizes at or below 0.8 mm, the requirement for septal lines was likely to be 0.4 mm (1.25 line pairs/mm).     

Echo planar perfusion imaging with high spatial and temporal resolution: methodology and clinical aspects

The purpose of the present study was to analyse specific advantages of calculated parameter images and their limitations using an optimized echo-planar imaging (EPI) technique with high spatial and temporal resolution. Dynamic susceptibility contrast magnetic resonance imaging (DSC-MRI) was performed in 12 patients with cerebrovascular disease and in 13 patients with brain tumours. For MR imaging of cerebral perfusion an EPI sequence was developed which provides a temporal resolution of 0.68 s for three slices with a 128 × 128 image matrix. To evaluate DSC-MRI, the following parameter images were calculated pixelwise: (1) Maximum signal reduction (MSR); (2) maximum signal difference (ΔSR); (3) time-to-peak (T_p); and (4) integral of signal-intensity-time curve until T_p (S_Int). The MSR maps were superior in the detection of acute infarctions and ΔSR maps in the delineation of vasogenic brain oedema. The time-to-peak (T_p) maps seemed to be highly sensitive in the detection of poststenotic malperfused brain areas (sensitivity 90 %). Hyperperfused areas of brain tumours were detectable down to a diameter of 1 cm with high sensitivity ( > 90 %). Distinct clinical and neuroradiological conditions revealed different suitabilities for the parameter images. The time-to-peak (T_p) maps may be an important advantage in the detection of poststenotic “areas at risk”, due to an improved temporal resolution using an EPI technique. With regard to spatial resolution, a matrix size of 128 × 128 is sufficient for all clinical conditions. According to our results, a further increase in matrix size would not improve the spatial resolution in DSC-MRI, since the degree of the vascularization of lesions and the susceptibility effect itself seem to be the limiting factors. Received: 24 December 1997; Revision received: 6 April 1998; Accepted: 19 May 1998     

A targeted contrast agent for magnetic resonance imaging of thrombus: implications of spatial resolution

A preparation of ultra-small superparamagnetic iron oxide (USPIO) particles coupled to an RGD peptide (RGD-USPIO) was investigated as an MR contrast agent, targeted to activated platelets, in both ex vivo and in vivo thrombus models. Thrombus visualization ex vivo was compared using RGD-USPIO and a non-targeted UPSIO. The influence of thrombus visualization on thrombus exposure time to RGD-USPIO (ex vivo) and on the spatial resolution of the MR image (ex vivo and in vivo) was assessed. RGD-USPIO resulted in better thrombus visualization than non-targeted USPIO ex vivo, and maximum enhancement was achieved after approximately one hour exposure time of the thrombus to RGD-USPIO. The ability to visualize the clots was highly dependent on the spatial resolution of the image. In vivo, an in-plane resolution of less than 0.2 x 0.2 mm(2) was required for good clot visualization after contrast enhancement. It is concluded that the achievable resolution and sensitivity is a potential limitation to the usefulness of active vascular targeting in MRI.     

16-MDCT in the detection of occult wrist fractures: a comparison with skeletal scintigraphy

OBJECTIVE: Our objective was to assess the potential use of MDCT in the detection of occult scaphoid fractures. Fifty-one patients with suspected radiographically occult scaphoid fractures at 10-14 days after trauma were investigated prospectively with skeletal scintigraphy and CT on the same day. Planar images of the wrist were taken 3 hr after IV injection of 400 MBq of (99m)Tc-methylene diphosphonate using a single-head gamma camera. CT was performed on a 16-MDCT machine using 0.75-mm detectors and reconstruction in 0.5-mm slices. Multiplanar reformatted images were then viewed in interactive cine mode. The examinations were reported independently, and discordant results were compared at follow-up. CT was positive for wrist fracture in 14 (27.4%) of 51 patients and skeletal scintigraphy in 23 (45.1%) of 51 patients. Even after retrospective review, there were seven discrepant cases (13.7%), all of which were positive for wrist fracture on scintigraphy but negative on CT. Four of these seven patients with discordant findings underwent further radiography at 6 weeks, which did not show fracture. CONCLUSION: Although CT was preferred by most patients and was quicker, scintigraphy appears to detect bony abnormality more frequently. However, there appears to be an interesting group of patients (7/51) with normal initial radiography findings but positive scintigraphy findings who would normally be considered to have a fracture but for whom CT results were negative. In some of these patients, the results of follow-up radiography at 6 weeks were also negative, suggesting that this group of patients warrants further study.     

High temporal and spatial resolution imaging of peripheral vascular malformations

Purpose:

To assess the performance of a recently developed 3D time‐resolved CE‐MRA technique, Cartesian Acquisition with Projection‐Reconstruction‐like sampling (CAPR), for accurate characterization and treatment planning of vascular malformations of the periphery.

Materials and Methods:

Twelve patient studies were performed (eight female, four male; average age, 33 years). The protocol consisted of three‐dimensional (3D) time‐resolved CE‐MRA followed by a single late phase T1‐weighted acquisition. Vascular malformations were imaged in the forearm, hand, thigh, and foot. Imaging evaluation was performed for accurate characterization of lesion type, identification of feeding and draining vessels, involvement with surrounding tissue, overall quality for diagnosis and treatment planning, and correlation with conventional angiography.

Results:

Time‐resolved CE‐MRA allowed for characterization of malformation flow and type. Feeding and draining vessels were identified in all cases. Overall quality for diagnosis and treatment planning was 3.58/4.0, and correlation with conventional angiography was scored as 3.89/4.0.

Conclusion:

The CAPR time series has been shown to portray the temporal dynamics and structure of vascular malformations as well as the normal vasculature with high quality. CAPR time‐resolved imaging is able to accurately characterize high and low flow lesions, allowing for pretreatment lesion assessment and treatment planning. Delayed imaging is important to capture complete filling of very slow flow vascular malformations. J. Magn. Reson. Imaging 2012;36:933–942. © 2012 Wiley Periodicals, Inc.     

16-Detector multislice CT in the detection of stress fractures: a comparison with skeletal scintigraphy

AIMS: To test the hypothesis that the improved resolution afforded by 16-detector computed tomography (CT) would translate to better stress fracture detection when compared with skeletal scintigraphy. MATERIALS AND METHODS: Thirty-three cases of suspected stress fractures in 26 patients were investigated using skeletal scintigraphy and 16-detector CT performed on the same day. Planar images of the lower limbs were taken 3h post-injection of 400MBq (99m)Tc-methylene diphosphonate ((99m)Tc-MDP). (99m)Tc-MDP uptake was quantified at suspected fracture sites. CT was performed using a 16-detector multisection machine employing 0.75mm detectors and images reconstructed in 0.5mm increments. Examinations were reported independently and discordant results were compared at follow-up. RESULTS: At initial reporting scintigraphy identified fractures in 13 of the 33 cases and CT identified four of the 33. In one case, on review of the CT images, a fracture was present in the distal fibula that was not initially identified. This resulted in eight scintigraphic-positive CT-negative discordant cases. The (99m)Tc-MDP uptake was significantly lower in the discordant fracture group compared with the concordant group (p<0.01). CONCLUSIONS: Despite technological advances in CT, scintigraphy appeared to detect more stress fractures. As such, multidetector CT should not be used as a routine initial investigation in stress fracture detection. The potential use of (99m)Tc-MDP quantification at fracture sites is of interest and may be worth further investigation.     

CT detection of serious internal and skeletal injuries in patients with pelvic fractures

RATIONALE AND OBJECTIVES: The purpose of this study was to determine the percentage of patients with known pelvic fractures who have additional findings of intraabdominal injury, as diagnosed at abdominal computed tomography (CT), and to determine if patients with specific types or patterns of fractures are more likely to have additional injuries. MATERIALS AND METHODS: The authors reviewed the medical records of 200 consecutive patients (125 women, 75 men; age range, 4-86 years) who had been admitted to a level 1 trauma center with osseous pelvic injury secondary to blunt trauma and who had undergone abdominal CT examinations. Abdominal CT findings in these patients were classified as negative, positive, or minimal and correlated with mechanism of pelvic fracture. RESULTS: Sixty-five (32%) of the 200 patients had negative CT findings, 43 (22%) had findings attributable to the trauma but required no follow-up, and 92 (46%) had positive findings that required nonsurgical management or exploratory laparotomy. Additional pelvic fractures were identified in 63 (32%) patients. The highest prevalence of additional injuries was in patients with Malgaigne fractures (four of 15, 27%) or bilateral pubic rami fractures (six of 18, 33%). CONCLUSION: CT examinations revealed that 135 (68%) of 200 patients with pelvic fractures secondary to blunt trauma had concomitant internal or skeletal injuries and that 92 (46%) patients had injuries severe enough to require nonsurgical management or exploratory laparotomy. Patients with bilateral pubic rami fractures or Malgaigne fractures were particularly prone to additional injuries; therefore, abdominal CT examinations are recommended in these patients.     

Polyp detection with MDCT: a phantom-based evaluation of the impact of dose and spatial resolution

OBJECTIVE: The objective of our study was to evaluate the impact of dose and spatial resolution on the detection of colonic polyps using a 4-MDCT scanner. MATERIALS AND METHODS: Twenty-four latex phantoms that simulate the large bowel and contain artificial polyps of different sizes and shapes were constructed. The polyps were divided into three size groups (diameter, 0-2, 2-5, and 5-10 mm) and were classified into four shape groups: pedunculated; broad-based; ulcerated or depressed; and sessile or flat. The colon phantoms were submerged in a water tank and scanned on a 4-MDCT scanner using 12 protocols with various settings of slice thickness, pitch, and tube current. The images were independently evaluated by three radiologists using axial 2D multiplanar reconstruction images and a 3D surface-rendering technique (fly-through). RESULTS: At a constant dose (i.e., dose-length product [DLP]), the polyp detection rate increased with increasing axial spatial resolution. For the standard protocol (2.50-mm slice thickness, 1.5 pitch), the detection rate for all polyp sizes decreased from approximately 70% at 100 mA to 55% at 40 mA. Between a 60- and 100-mA tube current, the detection rate for the largest polyps (> 5 mm) was almost constant, close to 90%. CONCLUSION: The detection of polyps in the large bowel using a standard protocol can be improved without dose penalty by increasing the axial spatial resolution of the image acquisition and adjusting the tube current setting. If the analysis can be restricted to polyps larger than 5 mm, the dose can be substantially reduced without compromising the detection rate.     

Embedded MR fluoroscopy: high temporal resolution real-time imaging during high spatial resolution 3D MRA acquisition.

A method termed "embedded fluoroscopy" for simultaneously acquiring a real-time sequence of 2D images during acquisition of a 3D image is presented. The 2D images are formed by periodically sampling the central phase encodes of the slab-select direction during the 3D acquisition. The tradeoffs in spatial and temporal resolution are quantified by two parameters: the "redundancy" (R), the fraction of the 3D acquisition sampled more than once; and the "effective temporal resolution" (T), the time between temporal updates of the central views. The method is applied to contrast-enhanced MR angiography (CE-MRA). The contrast bolus dynamics are portrayed in real time in the 2D image sequence while a high-resolution 3D image is being acquired. The capability of the 2D acquisition to measure contrast enhancement with only a 5% degradation of the spatial resolution of the 3D CE-MR angiogram is shown theoretically. The method is tested clinically in 15 CE-MRA patient studies of the carotid and renal arteries.     

应用压缩传感技术进行快速各向同性空间分辨率延迟钆强化心脏MR成像的初步研究

摘要目的评价各向同性空间分辨的延迟钆强化(LGE)MRI低维结构自学和阈值(LOST)的压缩传感采集和重建技术在评估左心房(LA)及左心室(LV)瘢痕的作用。材料与方法本研究通过伦理审查委员会审查,并符合HIPAA要求。