Performance evaluation of detector for digital radiography

Lo scopo di questo lavoro è la caratterizzazione fisica del flat panel PaxScan4030CB Varian, rivelatore di raggi X impiegato in un ampio spettro di applicazioni cliniche, dalla radiografia generale alla radiologia interventistica. Nell’ambito clinico, al fine di una diagnosi accurata, è necessario avere una buona qualità dell’immagine radiologica mantenendo il più basso livello di dose rilasciata al paziente. Elemento fondamentale per ottenere questo risultato è la scelta del rivelatore di radiazione X, che deve garantire prestazioni fisiche (contrasto, risoluzione spaziale e rumore) adeguati alla specifica procedura. Le metriche oggettive che misurano queste caratteristiche sono SNR (Signal-to-Noise Ratio), MTF (Modulation Transfer Function) ed NPS (Noise Power Spectrum), che insieme contribuiscono alla misura della DQE (Detective Quantum Efficiency), il parametro più completo e adatto a stabilire le performance di un sistema di imaging. L’oggettività di queste misure consente anche di mettere a confronto tra loro diversi sistemi di rivelazione. La misura di questi parametri deve essere effettuata seguendo precisi protocolli di fisica medica, che sono stati applicati al rivelatore PaxScan4030CB presente nel laboratorio del Centro di Coordinamento di Fisica Medica, Policlinico S.Orsola. I risultati ottenuti, conformi a quelli dichiarati dal costruttore, sono stati confrontati con successo con alcuni lavori presenti in letteratura e costituiscono la base necessaria per la verifica di procedure di ottimizzazione dell’immagine radiologica attraverso interventi sul processo di emissione dei raggi X e sul trattamento informatico dell’immagine (Digital Subtraction Angiography).

Intensified chemotherapy and dose-reduced involved-field radiotherapy in patients with early unfavorable Hodgkin's lymphoma: final analysis of the German Hodgkin Study Group HD11 trial

Combined-modality treatment consisting of four to six cycles of chemotherapy followed by involved-field radiotherapy (IFRT) is the standard of care for patients with early unfavorable Hodgkin's lymphoma (HL). It is unclear whether treatment results can be improved with more intensive chemotherapy and which radiation dose needs to be applied.

Real-Time Multimodal Retinal Image Registration for a Computer Assisted Laser Photocoagulation System

An algorithm for the real-time registration of a retinal video sequence captured with a scanning digital ophthalmoscope (SDO) to a retinal composite image is presented. This method is designed for a computer-assisted retinal laser photocoagulation system to compensate for retinal motion and hence enhance the accuracy, speed, and patient safety of retinal laser treatments. The procedure combines intensity and feature-based registration techniques. For the registration of an individual frame, the translational frame-to-frame motion between preceding and current frame is detected by normalized cross correlation. Next, vessel points on the current video frame are identified and an initial transformation estimate is constructed from the calculated translation vector and the quadratic registration matrix of the previous frame. The vessel points are then iteratively matched to the segmented vessel centerline of the composite image to refine the initial transformation and register the video frame to the composite image. Criteria for image quality and algorithm convergence are introduced, which assess the exclusion of single frames from the registration process and enable a loss of tracking signal if necessary. The algorithm was successfully applied to ten different video sequences recorded from patients. It revealed an average accuracy of 2.47 ± 2.0 pixels (∼23.2 ± 18.8 μm) for 2764 evaluated video frames and demonstrated that it meets the clinical requirements.

The production and composition of rat sebum is unaffected by 3 Gy gamma radiation

The aim of this work was to use metabolomics to evaluate sebum as a source of biomarkers for gamma-radiation exposure in the rat, and potentially in man. Proof of concept of radiation metabolomics was previously demonstrated in both mouse and rat urine, from the radiation dose- and time-dependent excretion of a set of urinary biomarkers.

Radiation doses along selected flight profiles during two extreme solar cosmic ray events

The radiation dose rates at flight altitudes may be hazardously increased during solar cosmic ray events. Within the scope of this paper we investigate the total accumulated radiation doses, i.e. the contribution of galactic and solar cosmic rays, during the two extreme solar cosmic ray events on 29 September 1989 and on 20 January 2005 along selected flight profiles. In addition, the paper discusses the consequences of possible solar cosmic ray flux approximations on the results of the radiation dose computations.

A review of full-body radiography in nontraumatic emergency medicine

This paper reports on the application of full-body radiography to nontraumatic emergency situations. The Lodox Statscan is an X-ray machine capable of imaging the entire body in 13 seconds using linear slit scanning radiography (LSSR). Nontraumatic emergency applications in ventriculoperitoneal (VP) shunt visualisation, emergency room arteriography (ERA), detection of foreign bodies, and paediatric emergency imaging are presented. Reports show that the fast, full-body, and low-dose scanning capabilities of the Lodox system make it well suited to these applications, with the same or better image quality, faster processing times, and lower dose to patients. In particular, the large format scans allowing visualisation of a greater area of anatomy make it well suited to VP shunt monitoring, ERA, and the detection of foreign bodies. Whilst more studies are required, it can be concluded that the Lodox Statscan has the potential for widespread use in these and other nontraumatic emergency radiology applications.

Comparison of contrast-enhanced multi-station MR angiography and digital subtraction angiography of the lower extremity arterial disease

PURPOSE: To compare diagnostic accuracy of multi-station, high-spatial resolution contrast-enhanced MR angiography (CE-MRA) of the lower extremities with digital subtraction angiography (DSA) as the reference standard in patients with symptomatic peripheral arterial occlusive disease. MATERIALS AND METHODS: Of 485 consecutive patients undergoing a run-off CE-MRA, 152 patients (86 male, 66 female; mean age, 71.6 years) with suspected peripheral arterial occlusive disease were included into our Institutional Review Board approved study. All patients underwent MRA and DSA of the lower extremities within 30 days. MRA was performed at 1.5 Tesla with a single bolus of 0.1 mmol/kg body weight of gadobutrol administered at a rate of 2.0 mL/s at three stations. Two readers evaluated the MRA images independently for stenosis grade and image quality. Sensitivity and specificity were derived. RESULTS: Sensitivity and specificity ranged from 73% to 93% and 64% to 89% and were highest in the thigh area. Both readers showed comparable results. Evaluation of good and better quality MRAs resulted in a considerable improvement in diagnostic accuracy. CONCLUSION: Contrast-enhanced MRA demonstrates good sensitivity and specificity in the investigation of the vasculature of the lower extremities. While a minor investigator experience dependence remains, it is standardizable and shows good inter-observer agreement. Our results confirm that the administration of Gadobutrol at a standard dose of 0.1 mmol/kg for contrast-enhanced runoff MRA is able to detect hemodynamically relevant stenoses. Use of contrast-enhanced MRA as an alternative to intra-arterial DSA in the evaluation and therapeutic planning of patients with suspected peripheral arterial occlusive disease is well justified. J. Magn. Reson. Imaging 2013;37:1427-1435. © 2012 Wiley Periodicals, Inc.

In Vitro and In Vivo Imaging Characteristics Assessment of Polymeric Coils Compared with Standard Platinum Coils for the Treatment of Intracranial Aneurysms

BACKGROUND AND PURPOSE:Conventional platinum coils cause imaging artifacts that reduce imaging quality and therefore impair imaging interpretation on intraprocedural or noninvasive follow-up imaging. The purpose of this study was to evaluate imaging characteristics and artifact production of polymeric coils compared with standard platinum coils in vitro and in vivo.MATERIALS AND METHODS:Polymeric coils and standard platinum coils were evaluated in vitro with the use of 2 identical silicon aneurysm models coiled with a packing attenuation of 20% each. DSA, flat panel CT, CT, and MR imaging were performed. In vivo evaluation of imaging characteristics of polymeric coils was performed in experimentally created rabbit carotid bifurcation aneurysms. DSA, CT/CTA, and MR imaging were performed after endovascular treatment of the aneurysms. Images were evaluated regarding visibility of individual coils, coil mass, artifact production, and visibility of residual flow within the aneurysm.RESULTS:Overall, in vitro and in vivo imaging showed relevantly reduced artifact production of polymeric coils in all imaging modalities compared with standard platinum coils. Image quality of CT and MR imaging was improved with the use of polymeric coils, which permitted enhanced depiction of individual coil loops and residual aneurysm lumen as well as the peri-aneurysmal area. Remarkably, CT images demonstrated considerably improved image quality with only minor artifacts compared with standard coils. On DSA, polymeric coils showed transparency and allowed visualization of superimposed vessel structures.CONCLUSIONS:This initial experimental study showed improved imaging quality with the use of polymeric coils compared with standard platinum coils in all imaging modalities. This might be advantageous for improved intraprocedural imaging for the detection of complications and posttreatment noninvasive follow-up imaging.

Whole-body computed tomography for multiple traumas using a triphasic injection protocol

To evaluate a triphasic injection protocol for whole-body multidetector computed tomography (MDCT) in patients with multiple trauma. Fifty consecutive patients (41 men) were examined. Contrast medium (300 mg/mL iodine) was injected starting with 70 mL at 3 mL/s, followed by 0.1 mL/s for 8 s, and by another bolus of 75 mL at 4 mL/s. CT data acquisition started 50 s after the beginning of the first injection. Two experienced, blinded readers independently measured the density in all major arteries, veins, and parenchymatous organs. Image quality was assessed using a five-point ordinal rating scale and compared to standard injection protocols [n = 25 each for late arterial chest, portovenous abdomen, and MDCT angiography (CTA)]. With the exception of the infrarenal inferior caval vein, all blood vessels were depicted with diagnostic image quality using the multiple-trauma protocol. Arterial luminal density was slightly but significantly smaller compared to CTA (P < 0.01). Veins and parenchymatous organs were opacified significantly better compared to all other protocols (P < 0.01). Arm artifacts reduced the density of spleen and liver parenchyma significantly (P < 0.01). Similarly high image quality is achieved for arteries using the multiple-trauma protocol compared to CTA, and parenchymatous organs are depicted with better image quality compared to specialized protocols. Arm artifacts should be avoided.

Comparative dose measurements by spiral tomography for preimplant diagnosis: the Scanora machine versus the Cranex Tome radiography unit

Objective. The purpose of this study was to determine the dose profile of the Cranex Tome radiography unit and compare it with that of the Scanora machine.Study design. The radiation dose delivered by the Cranex Tome radiography unit during the cross-sectional mode was determined. Single tooth gaps in regions 3 (16) and 30 (46) were simulated. Dosimetry was carried out with 2 phantoms, a head and neck phantom and a full-body phantom loaded with 142 thermoluminescent dosimeters (TLD) and 280 TLD, respectively; all locations corresponded to radiosensitive organs or tissues. The recorded local mean organ doses were compared with those measured in another study evaluating the Scanora machine.Results. Generally, dose values from the Cranex Tome radiography unit reached only 50% to 60% of the values measured for the Scanora machine. The effective dose was calculated as 0.061 mSv and 0.04 mSv for tooth regions 3 (16) and 30 (46), respectively. Corresponding values for the Scanora machine were 0.117 mSv and 0.084 mSv.Conclusion. Cross-sectional imaging in the molar region of the upper and the lower jaw can be performed with the Cranex Tome unit, which delivers only approximately half of the dose that the Scanora machine delivers.

Hypothetical mortality risk associated with spiral computed tomography of the maxilla and mandible

In the present study, dose measurements have been conducted following examination of the maxilla and mandible with spiral computed tomography (CT). The measurements were carried out with 2 phantoms, a head and neck phantom and a full body phantom. The analysis of applied thermoluminescent dosimeters yielded radiation doses for organs and tissues in the head and neck region between 0.6 and 16.7 mGy when 40 axial slices and 120 kV/165 mAs were used as exposure parameters. The effective dose was calculated as 0.58 and 0.48 mSv in the maxilla and mandible, respectively. Tested methods for dose reduction showed a significant decrease of radiation dose from 40 to 65%. Based on these results, the mortality risk was estimated according to calculation models recommended by the Committee on the Biological Effects of Ionizing Radiations and by the International Commission on Radiological Protection. Both models resulted in similar values. The mortality risk ranges from 46.2 x 10.6 for 20-year-old men to 11.2 x 10(-6) for 65-year-old women. Using 2 methods of dose reduction, the mortality risk decreased by approximately 50 to 60% to 19.1 x 10(-6) for 20-year-old men and 5.5 x 10(-6) for 65-year-old women. It can be concluded that a CT scan of the maxillofacial complex causes a considerable radiation dose when compared with conventional radiographic examinations. Therefore, a careful indication for this imaging technique and dose reduction methods should be considered in daily practice.

Martian sub-surface ionising radiation: biosignature and geology

The surface of Mars, unshielded by thick atmosphere or global magnetic field, is exposed to high levels of cosmic radiation. This ionising radiation field is deleterious to the survival of dormant cells or spores and the persistence of molecular biomarkers in the subsurface, and so its characterisation is of prime astrobiological interest. Here, we present modelling results of the absorbed radiation dose as a function of depth through the Martian subsurface, suitable for calculation of biomarker persistence. A second major implementation of this dose accumulation rate data is in application of the optically stimulated luminescence technique for dating Martian sediments. We present calculations of the dose-depth profile in the Martian subsurface for various scenarios: variations of surface composition (dry regolith, ice, layered permafrost), solar minimum and maximum conditions, locations of different elevation (Olympus Mons, Hellas basin, datum altitude), and increasing atmospheric thickness over geological history. We also model the changing composition of the subsurface radiation field with depth compared between Martian locations with different shielding material, determine the relative dose contributions from primaries of different energies, and discuss particle deflection by the crustal magnetic fields.

Tumors in the contralateral breast following radiation therapy for breast cancer

The proportional distribution of independent malignant tumors in the contralateral breast following treatment for breast cancer was investigated to assess the influence of scattered radiation as a cause of these tumors. In a population of 172 patients the proportion of contralateral tumors in each quadrant and the center (the nipple-areolar complex) was compared with the expected, or natural, distribution found in the general population, in the absence of radiation. The observed/expected ratio for contralateral tumors was 1.43 for the upper-inner quadrant; 0.97, lower-inner quadrant; 1.51, center; 0.76, upper-outer quadrant; and 0.64, lower-outer quadrant. In each quadrant, except the lower-inner, the observed/expected ratio differed from 1.00 with statistical significance at the 5% level (one-tail). The same analysis, stratified by age and menopausal status, showed a similar shift of tumors, with more than expected in the inner quadrants and center and less than expected in the outer quadrants, although the results did not show statistical significance at the 5% level for all strata. For each patient the mean absorbed radiation dose for each quadrant and center of the breast was estimated, based on measurements in a tissue-equivalent phantom. Among patients the doses ranged from 0.5 to 8 Gy; within individuals, doses to the inner quadrants typically were a factor of three times higher than doses to the outer quadrants. The results suggest that radiation may be a risk factor for contralateral breast tumors and warrants further investigation. ^

Monoenergetic computed tomography reconstructions reduce beam hardening artifacts from dental restorations

The aim of this study was to assess the potential of monoenergetic computed tomography (CT) images to reduce beam hardening artifacts in comparison to standard CT images of dental restoration on dental post-mortem CT (PMCT). Thirty human decedents (15 male, 58 ± 22 years) with dental restorations were examined using standard single-energy CT (SECT) and dual-energy CT (DECT). DECT data were used to generate monoenergetic CT images, reflecting the X-ray attenuation at energy levels of 64, 69, 88 keV, and at an individually adjusted optimal energy level called OPTkeV. Artifact reduction and image quality of SECT and monoenergetic CT were assessed objectively and subjectively by two blinded readers. Subjectively, beam artifacts decreased visibly in 28/30 cases after monoenergetic CT reconstruction. Inter- and intra-reader agreement was good (k = 0.72, and k = 0.73 respectively). Beam hardening artifacts decreased significantly with increasing monoenergies (repeated-measures ANOVA p < 0.001). Artifact reduction was greatest on monoenergetic CT images at OPTkeV. Mean OPTkeV was 108 ± 17 keV. OPTkeV yielded the lowest difference between CT numbers of streak artifacts and reference tissues (-163 HU). Monoenergetic CT reconstructions significantly reduce beam hardening artifacts from dental restorations and improve image quality of post-mortem dental CT.

Quality Assessment and Enhancement Method for high-resolution Fourier-Domain OCT Imaging of Retina Laser Lesions

We present an image quality assessment and enhancement method for high-resolution Fourier-Domain OCT imaging like in sub-threshold retina therapy. A Maximum-Likelihood deconvolution algorithm as well as a histogram-based quality assessment method are evaluated.