Use of imaging procedures in gallstone ileus

Gallstone ileus is a rare complication of cholecystolithiasis with a high mortality and a high rate of postoperative complications caused by the advanced age of the patients and the often delayed diagnosis. The article shows that the consistent use of conventional radiological methods helps to reduce the high incidence of undetected gallstone ileus. A plain film of the abdomen is mandatory because it yields important information on the presence of an ileus and allows to diagnose gallstone ileus if air in the biliary tree and an aberrantly located gallstone is visible. Signs of an ileus are a frequent finding on abdominal scout films (9 of 9 cases) while the additional signs are often absent (5 of 9 cases). Contrast x-ray studies of the intestine, especially the upper gastrointestinal series with water-soluble contrast media, are of importance because they can help in detecting biliary enteric fistulas or gallstones located in the intestine. Hence, the consistent use of this roentgenologic routine methods can promote the accuracy of correct preoperative diagnosis (4 of 7 cases).     

Sigmoid diverticulitis: diagnostic role of CT--comparison with barium enema studies

The diagnostic value of computed tomography (CT) and barium enema (BE) studies was evaluated prospectively in hospitalized patients with the presumptive diagnosis of acute sigmoid diverticulitis based on the presence of left-lower-quadrant pain and tenderness, fever, and leukocytosis. Of 56 patients, 11 had sigmoid diverticulitis confirmed at surgery and 16 by clinical response to medical therapy. CT, performed in all diverticulitis patients, had positive results in 93% (25 of 27). These compared favorably with BE study results, of which 80% (20 of 25) were positive. Neither examination had false-positive results. In the 29 patients who did not have diverticulitis, an alternative diagnosis was made by means of CT in 20, but in only three by means of BE studies. Many of the extracolonic abnormalities recognized at CT were clinically unexpected and necessitated emergency surgery. The excellent sensitivity and specificity of CT coupled with its versatility in the detection of extracolonic disease give it an advantage over contrast enema studies for diagnosis of sigmoid diverticulitis. CT should be the initial study in acutely ill patients, especially when the clinical features are atypical for sigmoid diverticulitis.     

Sixty-four multi-detector row computed tomography in multitrauma patient imaging: early experience

Sixty-four multi-detector row computed tomography (64-MDCT) offers the possibility of increasing the application of CT in multitrauma imaging. 64-MDCT affords significant increases in imaging speed while allowing for subisotropic voxel slice thicknesses. We have recently installed two 64-MDCT scanners in our Level I trauma center. Our routine protocols using these new scanners are detailed. Additionally, this new technology has made possible several novel protocols. These include an increased use of CT angiography in trauma imaging. The acquisition speed and table lengths available with 64-MDCT allow for whole-body scout images. These scout images may be used to plan complex, multistep CT studies incorporating pelvic and extremity angiography, when indicated, into a single study. Imaging speeds afforded by 64-MDCT allow for imaging in any number of phases, over any area to be imaged, all with a single initial bolus of contrast. Image quality afforded by 64-MDCT allows for increasing roles of MPR and 3D reformations. These alternatives to axial images are currently used both for primary interpretation by our trauma radiologists as well as for communication and use by our clinical colleagues. Technical challenges presented by 64-MDCT include further increases in the number of images generated. Currently, datasets may exceed 4,000 images when angiography is included in routine trauma protocols. Radiation doses are also an ever present concern. With the opportunity to image from head to toe in seconds with submillimeter slice thicknesses, radiologists must be constantly vigilant in their efforts to limit radiation. Novel techniques such as automated dose modulation currently offer means of reducing radiation doses. Though several technical challenges are faced, 64-MDCT represents an evolution in multitrauma imaging.     

Can computed tomography be relied upon to detect skull fractures?

Skull fractures were detected on plain films in 63 of 100 consecutive head-injured patients admitted to a neurosurgical unit. On routine computed tomographic (CT) lateral scout films, only 58% of lateral fractures were detected and there was a false positive rate of 12%. None of the anterior or posterior fractures was seen. On the routine axial CT cuts only 22.5% of fractures were detected. When examined at bone window settings, 76% of vertical and 37.5% of oblique linear fractures were detected but none of the horizontal fractures. All comminuted and depressed fractures were demonstrated when the axial cuts were examined at bone window settings and in all but one case by the scanogram and at routine brain window settings. Basal fracture extent was better shown by axial CT than on plain films, especially at bone window settings. Recommendations are made regarding the use of CT in the detection of skull fractures.     

Is intravenous contrast necessary for detection of clinically significant extracolonic findings in patients undergoing CT colonography?

Objective:

To determine whether intravenous contrast (IVC) is necessary for detection of extracolonic findings (ECFs) in patients undergoing CT colonography (CTC).

Methods:

We performed a retrospective review of CT findings in 179 cases of CTC studies performed over 18 months where both pre-contrast (NECT) and post-contrast (CECT) scans were performed in the prone and supine positions, respectively, in the same patients. All ECFs were recorded on a per patient basis and graded according to the colonography reporting and data system classification.

Results:

There was no significant change in E grade for the cohort (p = 0.171) between the NECT and CECT scans. On the CECT scans, additional findings were detected in 49.1% of patients. Overall, there were 27/179 (15.1%) patients graded E3 and 18/179 (10.1%) patients graded E4 on the CECT study. Compared with the NECT study, there was a decrease of 12.9% of patients graded E3 and no change in the number of patients graded E4.

Conclusion:

With IVC administration, additional ECFs are detected in nearly half of all patients. However, there was no increase in the number of patients with clinically significant lesions. The risk–benefit ratio of routine IVC administration for CTC in symptomatic patients thus requires further evaluation.

Advances in knowledge:

This study reviews the utility of IVC in CTC and is thus relevant to current clinical practice at many institutions.CT colonography (CTC) has emerged as an acceptable diagnostic tool for detection of colonic polyps and cancers. Numerous studies have corroborated the high sensitivity and specificity rates (>90%) in screening for large polyps.¹ Fewer studies have specifically examined the role of CTC for detection of extracolonic findings (ECFs) and the effect of these findings on subsequent patient treatment and cost.^2–8A distinct advantage of CTC over other diagnostic tests for colorectal abnormalities is the additional information provided by concomitant imaging of the extracolonic organs in the abdomen and pelvis, and, to a certain extent, the lower thorax. For example, early detection of extracolonic malignancies or metastases may make a difference to patient management and outcomes. The study by Veerappan et al³ showed that screening CTC without intravenous contrast (IVC) administration itself increased the odds of detection of high-risk lesions by 78%, half of which were ECFs. ECFs of at least moderate importance are seen in between 7% and 11% of patients.^2,4–8 Detection of these abnormalities, such as extracolonic cancers (e.g. renal cell carcinoma) and aortic aneurysms, can sometimes be beneficial.⁹The administration of IVC increases soft-tissue contrast and theoretically increases detection of ECFs. However, it has not been shown in a single patient cohort whether IVC increases detection of clinically significant ECFs in the setting of CTC. This is an important question because routine administration of IVC is not without adverse effects. These include increased cost and potential adverse events resulting from unnecessary subsequent work-up of incidentally detected ECFs. Hence, the purpose of our study was to determine whether IVC is necessary for the detection of clinically significant ECFs in patients undergoing CTC. The hypothesis of this study is that routine IVC in symptomatic patients undergoing CTC is not necessary for the detection of clinically significant ECFs.     

Can order of report prevent satisfaction of search in abdominal contrast studies?

RATIONALE AND OBJECTIVE: A previous receiver operating characteristic (ROC) study showed a systematic shift in decision thresholds for detecting plain film abnormalities on contrast examinations rather than plain radiographs. A previous eye-position study showed that this shift was based on a relative visual neglect of plain film regions on the contrast studies. We now determine whether an intervention that changes visual search can reduce this search-based satisfaction of search effect in contrast studies of the abdomen. MATERIALS AND METHODS: The authors measured detection of 23 plain film abnormalities in 44 patients who had plain film and contrast examinations. In 2 experiments, each plain-film and contrast study was examined independently in different sessions with observers providing a confidence rating of abnormality for each interpretation. There were 13 observers in the first experiment and 10 in the second experiment. The intervention required that for the contrast studies, observers first report abnormalities in the noncontrast region of the radiograph before reporting contrast findings. ROC curve areas for each observer in each treatment condition were estimated by using a proper ROC model. The analysis focused on changes in decision thresholds among the treatment conditions. RESULTS: The SOS effect on decision thresholds in abdominal contrast studies was replicated. Although reduced, the shift in decision thresholds in detecting plain film abnormalities on contrast examinations remained when observers were required to report those abnormalities before contrast findings. CONCLUSION: Reporting plain film abnormalities before reporting abnormalities demonstrated by contrast reduced somewhat the satisfaction of search effect on decision thresholds produced by a visual neglect of noncontrast regions on contrast examinations. This suggests that interventions that direct visual search do not offer protection against satisfaction of search effects that are based on faulty visual search.     

Follow-up of patients with previous treatment for coarctation of the thoracic aorta: comparison between contrast-enhanced MR angiography and fast spin-echo MR imaging

Regular follow-up is required in patients with previous intervention for coarctation of the aorta to detect recoarctation or aneurysm formation. In this study we describe the findings encountered on routine follow-up exams and we compare the use of contrast-enhanced 3D MR angiography (CE MRA) with fast spin-echo MRI (FSE) to study the thoracic aorta after previous intervention. In 51 consecutive patients previously treated for aortic coarctation, 74 MR studies of the thoracic aorta were performed during a 2-year period using CE MRA and FSE MRI. The thoracic aorta was evaluated for abnormalities of course, caliber, shape, and pathology of side branches. The CE MRA and FSE MRI studies were evaluated side by side by consensus of two reviewers evaluating which MR technique depicted the abnormalities of the thoracic aorta the best. Of 74 exams, six clinically important abnormalities were found: four aneurysms and two restenoses. Two small pseudoaneurysms were missed on the FSE studies. Contrast-enhanced MRA was judged to visualize aortic abnormalities better than FSE (47 of 74 MR studies) especially for the transverse aortic arch, coarctation site, left subclavian artery, and aortic arch configuration. For the ascending aorta and distal descending aorta, CE MRA and FSE performed equally well. Aortic diameters measured at four levels in the first 18 MRI studies showed no significant differences in diameter when measured by FSE or CE MRA (p = not significant). Clinically important abnormalities, such as aneurysm formation and restenosis, can be present years after treatment for aortic coarctation. In the regular follow-up of these patients, CE MRA may provide additional diagnostic information compared with FSE and should be included as part of the routine exam. Received: 3 April 2000; Revised: 5 July 2000; Accepted: 7 July 2000     

Extracolonic findings in patients undergoing abdomino-pelvic CT for suspected colorectal carcinoma in the frail and disabled patient

AIM: The aims of this study were to evaluate the extracolonic findings identified in patients undergoing minimal preparation abdomino-pelvic CT in place of barium enema or colonoscopy for the detection of possible colorectal carcinoma. MATERIALS AND METHODS: The CT technique involved helical acquisition (10 mm collimation, 1.5 pitch) following 2 days of preparation with oral contrast medium only. Extracolonic findings were evaluated in the light of subsequent follow-up and accuracy. The evaluation included assessment of the potential contribution of the extracolonic finding(s) to staging the cancer in the subset of patients who had colorectal carcinoma, and to account for the patients' presenting symptoms and signs in the remaining patients. RESULTS: A total of 344 extracolonic findings were detected in 261 CT examinations, from amongst a total of 1077 cases (24%). Extracolonic findings were potentially important in staging in 32 of the 98 (33%) cases subsequently found to have colorectal cancer. There were 284 extracolonic findings amongst the 221 cases who proved not have colorectal cancer. One hundred and twenty-four (44%) of these 284 findings were actively followed up by clinicians, and 33 (12%) ultimately had a surgical intervention. Fifty-six percent (160/284) of the findings were determined to be correct (by further investigation, autopsy, and/or clinical follow-up); the remainder were incorrect or indeterminate (n = 56) or had no follow-up (n = 68). The commonest extracolonic findings were focal liver lesions (found in 42/1077, 4%) and abdominal aortic aneurysms (31/1077, 3%). Twenty-four (24/1077, 2%) previously unknown extracolonic malignancies were detected. Ten percent (106/1077) of the patients had extracolonic findings that could potentially have accounted for their presenting symptoms. CONCLUSIONS: CT has the added benefit, compared with colonoscopy and barium enema, of not just evaluating the colon but also of detecting extracolonic abnormalities. Such findings may be useful in staging the cancer, may explain the patient's presenting symptoms, and may detect other potentially serious disorders.     

Incidental lesions found on CT colonography: their nature and frequency

CT colonography has been used to detect colonic polyps and cancers, but its effect in practice will also be influenced by the frequency with which extracolonic lesions of various types are detected. We performed a systematic review of the types of incidental lesions found on CT colonography. This is necessary to model the benefits and harms of detecting extracolonic lesions. Primary clinical studies of extracolonic findings on CT colonography were identified from electronic databases, scanning reference lists and hand searches of relevant journals and conference proceedings. A data collection proforma was used to collect information on extracolonic findings. 17 discreet studies were identified, involving 3488 patients. In total 40% of patients were recorded to have abnormalities and many had more than one abnormality. Nearly 14% of patients had further investigations and 0.8% were given immediate treatment. Extracolonic cancers were detected in 2.7% (0.9% had N0M0 cancers) and 0.9% had an aortic aneurysm. The number of extracolonic findings was high in all studies. While only a small population were judged "important", the prevalence of serious lesions outside the colon was nevertheless higher than in many other screening programs.     

Digital panoramic radiography: a clinical survey

The application of digital panoramic radiography with photostimulable phosphors to dental diagnosis was evaluated in 500 patients. Comparative intraoral films of selected groups of teeth and electronic magnifications of the same portion of the arches were obtained in 63 cases. Digital images improved the quality of dental examinations compared with film radiographs. The possibility of contrast modulation was helpful to compensate for the different radiographic densities of the arches and to improve the visibility of gingival soft tissues. In addition, digital radiography reduced the radiation dose administered to the patient. The use of digital panoramic radiography is proposed as a substitute for film studies in all hospitals where a central unit for digital radiology is available. Correspondence to: R. Nessi     

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.     

Contrast improvement in a new radiotherapy imaging system

PURPOSE: The aim of this paper is to compare the EC-L Kodak system for radiation therapy beam localization with a conventional one that could be daily employed in a radiotherapy department. BACKGROUND: The main purpose of portal images is to verify the treatment volume in actual clinical conditions. Low contrast is the main constraint affecting portal film image. METHODS: Kodak proposes a new imaging system (film and cassette) characterized by contrast enhancement as imaging standard for radiotherapy. The evaluation of system contrast was carried out by using a step-wedge consisting in 4 60 x 60 mm plexiglas steps and an anthropomorphic phantom. Portal films were exposed to a 6 MV photon beam by a linear accelerator (Varian Clinac 1800) with a 250 x 340 mm field size at the 1000 mm source film distance. The 2 imaging system performances were evaluated analyzing the image optical density. RESULTS: The use of the Kodak system results in a real contrast improvement, so it is satisfactory to describe the field placement as to the region of interest. CONCLUSIONS: The most critical characteristic attaining this method regards low contrast, i. e. the small optical density difference existing between different anatomical regions on the film. Since radiographic techniques can significantly influence quality of portal films, the adequate choice of film and screen combination, as well as the exposure technique is particularly useful in a radiotherapy quality assurance program.     

A quality study of 35 mm, miniaturization of full-size radiographic film

Twenty-one radiologists with 6 months--25 years experience judged the quality and the possibilities for the routine use of miniaturized full-size radiographic films for long time archiving. Twenty-eight examinations on full-size radiographs were photographed on 35 mm. film. After mounting in transparent jackets, the miniaturized films were read with enlarging equipment and diagnoses and quality noted. Comparison was later made with the originals. The consensus was that the quality of the miniaturized film was good enough to permit their use for long-term archiving purposes and subsequent comparison with future full-size radiographs. The use of reading equipment was not considered tedious.     

Extracolonic abnormalities discovered incidentally at CT colonography in a male population

PURPOSE: To evaluate prospectively the prevalence of incidental extracolonic findings at computed tomographic (CT) colonography and to estimate the cost of their imaging work-up in male patients with high and those with average risk of colorectal cancer. MATERIALS AND METHODS: This study was approved by the institutional review board, and informed consent was obtained from all patients. The study was compliant with requirements of the Health Insurance Portability and Accountability Act. CT colonography was performed in 500 men (mean age, 62.5 years). Of these patients, 194 (38.8%) were at average risk for colorectal cancer and presented for routine screening. The other 306 (61.2%) were at high risk for colorectal cancer. Extracolonic findings were recorded and categorized as either clinically important or clinically unimportant. Clinically important findings were defined as those that necessitated further diagnostic studies or medical or surgical follow-up. The cost of additional imaging required to further characterize important lesions was estimated. Chart review was performed (mean length of follow-up, 3.6 years) to determine whether any important findings were missed at CT colonography. The Fisher exact test was used to determine whether there was a difference between the percentages of average- and high-risk patients with extracolonic findings. RESULTS: Of the 500 patients in the study, 315 (63.0%) had extracolonic findings, and 45 (9.0%) had clinically important extracolonic findings. Of the 596 extracolonic findings identified, 50 (8.4%) were thought to be clinically important. The mean additional cost to work up important findings was $28.12 per CT colonographic examination. There were no significant differences between average-risk and high-risk patients in the percentages of extracolonic findings (P = .25) or clinically important extracolonic findings (P = .11). CONCLUSION: A substantial number of both average- and high-risk patients undergoing CT colonography will be found to have clinically important extracolonic findings. There was no increased morbidity or mortality associated with the additional evaluation of extracolonic findings. The cost of evaluating these lesions is low, given the potential for positive effects on patient care.     

Test report on the system components for film processing by the middle-format technology

Industrially developed accessories for use with medium-format equipment, which have been tested in a-clinical settery, were evaluated separately. The automatic mounting system (Delcadro) with the plastic mount (Cadrix) was accepted by all of our colleagues, and was rated as an advantage, with hardly any reservations. A slight modification is needed in the design of the mounts. This equipment would be a desirable addition to our own equipment for routine work. The daylight system (camera magazine and feeder) is, in principle, certainly a step in the right direction. Handling of the magazine proved to be too complicated and it was prone to malfunctions. Simplification, especially of the loading mechanism, would be desirable. The film feeder is designed for use with conventional roll processing machines. In our opinion, a feeder will always be put to full use if the films processed in this machine are mainly or exclusively of middle format; the darkroom is not permanently staffed and/or adaptation to an existing daylight system (large formats) has already been effected and/or depending on availability, both large and medium size-formats can be processed fully automatically as quickly as possible. However, if films of various formats are processed by an assistant in a darkroom, it is possible to deal with the total quantity of films faster than with a feeder by inserting 3 or 4 medium-format films (or 2 or 3 large-format films) simultaneously. The Heliomat film viewer offers impressive reproductions of 100 mm film on a glare-free glass screen.(ABSTRACT TRUNCATED AT 250 WORDS)     

Simplifying radiological examinations. Can it really be done in urography?

The value of commonly used routine films obtained at excretory urography was assessed in 565 patients. For a high level of confidence following films are recommended: Initial zonographic cut over the kidneys. A-P film covering bladder, ureters and as much as possible of the kidneys. Immediate post contrast medium injection film. Plain film or zonographic (tomographic) cut over the kidneys 10 min. later. Immediate post compression film. (Possible) post void film. The shorter urograms suggested by other authors are probably giving such a low level of confidence that other examinations may be requested as supplements.     

Radiology and the tooth

Radiological examination of the tooth and its appendages (periodontium) was poorly defined for a long time. It is based on a panoramic film, constituting a real scout film often completed by occlusive and intraoral films. The long-cone retro-alveolar assessment allows exact evaluation of dental and periodontal disease and determination of its nature (periodontitis, complex active periodontitis, etc.). Apart from malignant diseases, the CT scan is virtually only used in implantology assessments.     

Initial chest radiography in the neonatal intensive care unit: value of the lateral view.

This study was designed to assess the diagnostic efficacy of the routine lateral chest film in symptomatic newborn infants. The initial anteroposterior chest film was supplemented by alateral view in 53 consecutive patients on admission to the newborn intensive care unit. Subsequently three radiologists and two neonatologists performed independent analysis of the anterposterior films with and without the lateral view. A total of 530 observations were tabulated. Assessment of degree of lung inflation and discovery of abnormalities of the heart, mediastinum, and trachea were unaffected by the use of the lateral radiograph. A correct primary diagnosis was made in 74% of all cases by the anteroposterior chest film alone and in 71% by the anteroposterior/lateral series. Degree of confidence in the primary diagnosis did not change when the lateral chest radiograph was added. There was no appreciable difference in detection of complicatins of the primary disease in either series. We conclude that the risks (e.g., radiation and environmental disturbance) of the routine admission lateral chest radiograph are substantially greater than any benefits to be gained.     

The use of forced flexion/extension views in the obtunded trauma patient

OBJECTIVE: To determine whether forced flexion/extension (F/E) films for "clearing" the cervical spine in unconscious or semiconscious patients are useful or actually dangerous. DESIGN AND PATIENTS: Of 810 patients admitted for blunt trauma over a 5-year period, 479 patients whose films and charts were available received passive F/E film views of the cervical spine. Of these, 447 were reviewed retrospectively in masked fashion for any exacerbation of neurological changes subsequent to the procedure and with respect to the final neurological status at discharge. RESULTS: Twenty-nine patients (6%) had various abnormalities including fractures and ligamentous injuries seen on the initial films. Following forced F/E films no change was made in the diagnosis of 23 patients. Of the remaining six patients, two required no treatment, two only required the use of a collar but two did have surgical intervention, this decision being based on the findings seen in the initial films. However, 285 films (59%) were judged inadequate due either to inadequate F/E (150 patients, 31%) or poor visualization (194 patients, 40%). There were three false positives all subsequently cleared by other studies and there were no false negatives. From the chart review, there were no complications or deaths attributable to the procedure. CONCLUSION: Although we were unable to find any complication or deaths directly attributable to the procedure, the clinicians abandoned passive F/E views in obtunded patients on the grounds of expense. Our present method of "clearing" a cervical spine in an obtunded patient is a cross-table lateral radiograph followed by a high-resolution thin-slice CT scan with sagittal and coronal reconstruction. We are against the use of routine MRI studies and of a forced F/E view in these patients.     

Characterization of new portal film systems for radiotherapy verification.

Portal images are an important verification tool in radiotherapy. Their use has been limited by their poor image quality, which is due to the inherent lack of contrast at megavoltage energies. Recently CEA and Kodak have introduced new portal film-cassette systems with much improved contrast. We have determined the H-D curves for these systems and found the gamma (gamma) for the CEA system (8.5) to be larger than that for the Kodak EC-L system (6.3). The optimal doses were CEA TLF 1.2 cGy, CEA TVS 15.9 cGy and Kodak EC-L 1.5 cGy. We also obtained phantom images that were evaluated by 11 radiotherapists. They ranked the CEA B High Plus cassette with CEA TVS film the highest, followed by the Kodak EC-L system. Some clinical films of a lateral pelvis are also presented, to demonstrate the improvement in image quality with these new film systems as compared with conventional portal films.