Sabina Strocchi

Comparative study of jaws with multislice computed tomography and cone-beam computed tomography

PurposeThe aim of this study was to compare the dosimetric and diagnostic performance of multislice computed tomography (MSCT) and cone-beam computed tomography (CBCT) in the study of the dental arches.Materials and methodsEffective dose and dose to the main organs of the head and neck were evaluated by means of thermoluminescent dosimeters (TLDs) placed in an Alderson Rando anthropomorphic phantom and using a standard CBCT protocol and an optimised MSCT protocol. Five patients with occlusal plane ranging from 54 cm to 59 cm who needed close follow-up (range 1–3 months) underwent both examinations. Image quality obtained with CBCT and MSCT was evaluated.ResultsEffective dose and dose to the main organs of the head and neck were higher for MSCT than for CBCT. Image quality of CBCT was judged to be equivalent to that of MSCT for visualising teeth and bone but inferior for visualising soft tissues. Beam-hardening artefacts due to dental-care material and implants were weaker at CBCT than at MSCT.ConclusionsWhen panoramic radiography is not sufficient in the study of the teeth and jaw bones, CBCT can provide identical information to MSCT, with a considerable dose reduction. MSCT is, however, indicated when evaluation of soft tissue is required.RiassuntoObiettivoScopo di questo lavoro è confrontare le performances dosimetriche e diagnostiche di tomografia computerizzata multidetettore (TCMD) e tomografia computerizzata a fascio conico (TCFC) nello studio delle arcate dentarie.Materiali e metodiSi è provveduto alla misurazione della dose alle strutture di capo e collo e della dose efficace con dosimetri a termoluminescenza (TLD) posti in un fantoccio antropomorfo Alderson Rando utilizzando un protocollo TCFC ed uno TCMD ottimizzato. Sono stati esaminati 5 pazienti, con circonferenza al piano occlusale entro un range prestabilito (54–59 cm) e che avevano necessità di effettuare controlli ravvicinati nel tempo (range 1-3 mesi), con entrambi i sistemi TC ed è stata valutata la qualità delle immagini ottenute.RisultatiLa dose efficace agli organi è superiore per la TCMD rispetto alla TCFC. La qualità delle immagini della TCFC è stata giudicata sovrapponibile alla TCMD nello studio dei denti e dell’osso, inferiore nella valutazione dei tessuti molli. Artefatti da indurimento del fascio dovuti alla presenza di materiale medicamentoso e protesico incidono negativamente sulla qualità dell’immagine maggiormente nel caso della TCMD rispetto alla TCFC.ConclusioniLo studio delle strutture ossee può essere effettuato, se la radiografia ortopanoramica non è sufficiente, mediante TCFC, che fornisce informazioni sovrapponibili a quelle della TCMD con notevole risparmio di dose; la TCMD è indicata qualora sia necessario valutare anche i tessuti molli.

Optimisation of multislice computed tomography protocols in angio–CT examinations

Purpose.The aim of this paper is to explain a general procedure for the optimisation of multislice computed tomography (MSCT) protocols.Materials and methods.Four angio–CT protocols with a GE LightSpeed Plus 4–slice CT scanner were considered. Effective doses were computed for a sample of patients. First the dose was optimised for arterial–phase scans on a standard patient and adapted to the weight of individual patients with a scaling factor.Results.The mean effective dose for an angio–CT examination ranged from 18.8 mSv to 28.8 mSv, depending on the protocol adopted. Following the optimisation procedure, we drew up a table indicating tube current values for each patient weight. Calculation of the effective dose before and after the optimisation procedure revealed a dose reduction of about 40%.Conclusions.Angio–CT examinations deliver high doses, but these doses can be reduced without affecting image quality.

Functional magnetic resonance imaging: Comparison between activation maps and computation pipelines in a clinical context

In this study new evaluation strategies for comparing different Statistical Parametric Maps computed from fMRI time-series analysis software tools are proposed. The aim of our work is to assess and quantitatively evaluate the statistical agreement of activation maps. Some pre-processing steps are necessary to compare SPMs (Statistical Parametric Maps), including segmentation and co-registration. The study of the statistical agreement is carried out following two ways. The first way considers SPMs as the result of two classification processes and extracts confusion matrix and Cohens kappa index to assess agreement. Some considerations will be made on the statistical dependence of classes and a new formulation of kappa index will be used for overcoming this problem. The second way considers SPMs as two 3D images, and computes the similarity of SPMs images with a fuzzy formulation of the Jaccard Index. Several experiments were conducted both to assess the performance of the proposed evaluation tools and to compare activation maps computation pipelines from two widely used software tools in a clinical context.

Dedicated dental volumetric and total body multislice computed tomography: a comparison of image quality and radiation dose

Aim of this work is to compare the performances of a Xoran Technologies i-CAT Cone Beam CT for dental applications with those of a standard total body multislice CT (Toshiba Aquilion 64 multislice) used for dental examinations. Image quality and doses to patients have been compared for the three main i-CAT protocols, the Toshiba standard protocol and a Toshiba modified protocol. Images of two phantoms have been acquired: a standard CT quality control phantom and an Alderson Rando® anthropomorphic phantom. Image noise, Signal to Noise Ratio (SNR), Contrast to Noise Ratio (CNR) and geometric accuracy have been considered. Clinical image quality was assessed. Effective dose and doses to main head and neck organs were evaluated by means of thermo-luminescent dosimeters (TLD-100) placed in the anthropomorphic phantom. A Quality Index (QI), defined as the ratio of squared CNR to effective dose, has been evaluated. The evaluated effective doses range from 0.06 mSv (i-CAT 10 s protocol) to 2.37 mSv (Toshiba standard protocol). The Toshiba modified protocol (halved tube current, higher pitch value) imparts lower effective dose (0.99 mSv). The conventional CT device provides lower image noise and better SNR, but clinical effectiveness similar to that of dedicated dental CT (comparable CNR and clinical judgment). Consequently, QI values are much higher for this second CT scanner. No geometric distortion has been observed with both devices. As a conclusion, dental volumetric CT supplies adequate image quality to clinical purposes, at doses that are really lower than those imparted by a conventional CT device.

Dosimetric and image quality assessment of different acquisition protocols of a novel 64-slice CT scanner

Dose and image quality assessment in computed tomography (CT) are almost affected by the vast variety of CT scanners (axial CT, spiral CT, low-multislice CT (2-16), high-multislice CT (32-64)) and imaging protocols in use. Very poor information is at the moment available on 64 slices CT scanners. Aim of this work is to assess image quality related to patient dose indexes and to investigate the achievable dose reduction for a commercially available 64 slices CT scanner. CT dose indexes (weighted computed tomography dose index, CTDIw and Dose Length Product, DLP) were measured with a standard CT phantom for the main protocols in use (head, chest, abdomen and pelvis) and compared with the values displayed by the scanner itself. The differences were always below 7%. All the indexes were below the Diagnostic Reference Levels defined by the European Council Directive 97/42. Effective doses were measured for each protocol with thermoluminescent dosimeters inserted in an anthropomorphic Alderson Rando phantom and compared with the same values computed by the ImPACT CT Patient Dosimetry Calculator software code and corrected by a factor taking in account the number of slices (from 16 to 64). The differences were always below 25%. The effective doses range from 1.5 mSv (head) to 21.8 mSv (abdomen). The dose reduction system of the scanner was assessed comparing the effective dose measured for a standard phantom-man (a cylinder phantom, 32 cm in diameter) to the mean dose evaluated on 46 patients. The standard phantom was considered as no dose reduction reference. The dose reduction factor range from 16% to 78% (mean of 46%) for all protocols, from 29% to 78% (mean of 55%) for chest protocol, from 16% to 76% (mean of 42%) for abdomen protocol. The possibility of a further dose reduction was investigated measuring image quality (spatial resolution, contrast and noise) as a function of CTDIw. This curve shows a quite flat trend decreasing the dose approximately to 90% and a sharp fall below that value. A significant decrease in the effective dose to the patient, around 40%, was found; image quality analysis shows a further 10% dose reduction possibility.

fMRI analysis software tools: an evaluation framework

Performance comparison of functional Magnetic Resonance Imaging (fMRI) software tools is a very difficult task. In this paper, a framework for comparison of fMRI analysis results obtained with different software packages is proposed. An objective evaluation is possible only after pre-processing steps that normalize input data in a standard domain. Segmentation and registration algorithms are implemented in order to classify voxels belonging to brain or not, and to find the non rigid transformation that best aligns the volume under inspection with a standard one. Through the definitions of intersection and union of fuzzy logic an index was defined which quantify information overlap between Statistical Parametrical Maps (SPMs). Direct comparison between fMRI results can only highlight differences. In order to assess the best result, an index that represents the goodness of the activation detection is required. The transformation of the activation map in a standard domain allows the use of a functional Atlas for labeling the active voxels. For each functional area the Activation Weighted Index (AWI) that identifies the mean activation level of whole area was defined. By means of this brief, but comprehensive description, it is easy to find a metric for the objective evaluation of a fMRI analysis tools. Trough the first evaluation method the situations where the SPMs are inconsistent were identified. The result of AWI analysis suggest which tool has higher sensitivity and specificity. The proposed method seems a valid evaluation tool when applied to an adequate number of patients.

Digital breast tomosynthesis (DBT) versus full field digital mammography (FFDM): comparison of a system performance using a contrast detail phantom

To evaluate performance (image signal to noise ratio) of a digital mammographic system working in 2D planar versus tomosynthesis modality, a contrast detail phantom was developed embedding 1 cm plexyglas, including 49 holes of different diameter and depth, between two layers containing a breast simulating material. The acquisition protocol included 15 low dose projections (reconstructed 1mm-thick slices) and a 2D view. Using an automatic software analysis tool, the signal difference to noise ratio (SDNR) was evaluated. SDNR in the DBT images was about a factor two higher than with FFDM (P<1E-4). A more complete visual detection experiment is underway.

A Quantitative Method for the Evaluation of Spatial Resolution in Quality Control of B-mode Ultrasound Images:

The work describes a method to quantitatively evaluate spatial resolution in B-mode quality control images as radial modulation transfer function (MTF). The method is easy to use in in-field quality assurance programs in clinical institutions, as it is fast and can be performed with the help of phantoms that are already used for routine quality control. It uses a round insert with different echogenic characteristics compared with the phantom background. The method was automated with a MATLAB® routine, which can be run in full automatic mode or with a grade of interaction by the user, as is sometimes necessary with low-quality images. Radial MTF was evaluated for several ultrasound (US) images produced with different clinical US scanners from various vendors and equipped with different types of transducers (linear, convex, sector, vector) working at various frequencies (from 2 to 14 MHz) and with different modalities. It was also evaluated on various computed tomography (CT) images including round inserts. This was done to compare these results with the MTF calculated from the same images using the well-known method from the point spread function (PSF) of a high-contrast bead. Our radial MTF method, adapted to the specific characteristics of US images, was found to be reasonably robust and in line with other methods commonly used for USs (e.g., the pin method, which has repeatability issues) and in other fields, such as X-ray CT.

Endovascular Treatment of Acute Basilar Artery Occlusion: Registro Endovascolare Lombardo Occlusione Basilar Artery (RELOBA) Study Group Experience

BACKGROUND Acute basilar artery occlusion (BAO) is considered among the most severe medical emergencies, with very high morbidity and mortality. The aims of this study are to present 5 years experience of 12 centers in Lombardy region on BAO endovascular treatment and to evaluate prognostic factors that may improve clinical outcomes and recanalization rates. MATERIALS AND METHODS Registro Endovascolare Lombardo Occlusione Basilar Artery (RELOBA) registry is a retrospective multicentric collection of patients with acute BAO who underwent endovascular treatment between 2010 and 2015. A total of 102 patients (mean age 65 years) were included. Clinical, procedural, and neuroradiological data were collected. Angiographic results (Treatment in Cerebral Ischemia scale [TICI] score 2b-3) were assessed by each centers interventional neuroradiologist. Good clinical outcome was considered as a modified Rankin Scale score ranging between 0 and 2 in a 3-month follow-up. RESULTS Thirty-nine percent of patients showed good clinical outcome at 3 months. Mortality rate was 30%. TICI 2b-3 was achieved in 62% of patients. Univariate analysis showed that age, National Institutes of Health Stroke Scale (NIHSS) at onset, time to recanalization, and TICI score were all statistically significant clinical outcome predictors (P < .05). Multivariate logistic regression showed that time to recanalization, age, and NIHSS at onset were significant independent predictors of good outcome. CONCLUSIONS BAO treatment needs more efforts to assure patients better clinical outcomes. Mechanical thrombectomy is feasible and effective in patients with acute BAO. These results must be confirmed by further prospective studies within randomized controlled settings.

Computation and management of weighted activation vectors in support to fMRI analysis of clinical subjects

ABSTRACT In the present work, we investigate the usefulness of a new representation of the results obtained by fMRI data analysis, named weighted activation vector (WAV), built based on statistical parametric mapping. A software package for the generation and management of WAVs is illustrated. It is designed to support single-subject, multi-temporal and collective brain tumour studies. As seen in our experimental context, the combined use of WAVs and statistical parametric maps (SPMs) improves the quality of medical decisions before and after neurosurgical practice. Clustering techniques applied to WAVs can be efficiently analysed and optimised in an attempt to discover relevant properties of collective data.