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PURPOSE: To investigate the displacement forces and image artifacts associated with passive medical implants for recently-developed low-field (<100 mT) MRI systems, and to compare these with values from higher field strengths used for clinical diagnosis. METHODS: Setups were constructed to measure displacement forces in a permanent magnet-based Halbach array used for in vivo MRI at 50 mT, and results compared with measurements at 7 T. Image artifacts were assessed using turbo (fast) spin echo imaging sequences for four different passive medical implants: a septal occluder, iliac stent, pedicle screw and (ferromagnetic) endoscopic clip. Comparisons were made with artifacts produced at 1.5, 3 and 7 T. Finally, specific absorption rate (SAR) simulations were performed to determine under what operating conditions the limits might be approached at low-field. RESULTS: Displacement forces at 50 mT on all but the ferromagnetic implant were between 1 and 10 mN. Image artifacts at 50 mT were much less than at clinical field strengths for all passive devices, and with the exception of the ferromagnetic clip. SAR simulations show that very long echo train (>128) turbo spin echo sequences can be run with short inter-pulse times (5-10 ms) within SAR limits. CONCLUSIONS: This work presents the first evaluation of the effects of passive implants at field strengths less than 100 mT in terms of displacement forces, image artifacts and SAR. The results support previous claims that such systems can be used safely and usefully in challenging enviroments such as the intensive care unit.
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Artefatos , Imãs , Imageamento por Ressonância Magnética , Próteses e ImplantesRESUMO
Modern clinical MRI systems utilise very high magnetic fields strengths to produce high resolution images of the human body. The high up-front and maintenance cost of these systems means that much of the world lacks access to this technology. In this paper we propose a low cost, head-only, homogenous Halbach magnet array with the potential for paediatric neuroimaging in low-resource settings. The homogeneity of the Halbach array is improved by allowing the diameter of the Halbach array to vary along its length, and also adding smaller internal shim magnets. The constructed magnet has a bore diameter of 27â¯cm, mean B0 field strength of 50.4â¯mT and a homogeneity of 2400â¯ppm over a 20â¯cm diameter spherical volume. The level of homogeneity of the system means that coil-based gradients can be used for spatial encoding which greatly increases the flexibility in image acquisition. 3D images of a "brain phantom" were acquired over a 22â¯×â¯22â¯×â¯22â¯cm field of view with a 3.5â¯mm isotropic resolution using a spin-echo sequence. Future development of a low-cost gradient amplifier and an open-source spectrometer has the potential of offering a fully open-source, low-cost MRI system for paediatric neuroimaging in low-resource settings.
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White matter (WM) perfusion has great potential as a physiological biomarker in many neurological diseases. Although it has been demonstrated previously that arterial spin labeling magnetic resonance imaging (ASL-MRI) enables the detection of the perfusion-weighted signal in most voxels in WM, studies of cerebral blood flow (CBF) in WM by ASL-MRI are relatively scarce because of its particular challenges, such as significantly lower perfusion and longer arterial transit times relative to gray matter (GM). Recently, ASL with a spectroscopic readout has been proposed to enhance the sensitivity for the measurement of WM perfusion. However, this approach suffers from long acquisition times, especially when acquiring multi-phase ASL datasets to improve CBF quantification. Furthermore, the potential increase in the signal-to-noise ratio (SNR) by spectroscopic readout compared with echo planar imaging (EPI) readout has not been proven experimentally. In this study, we propose the use of time-encoded pseudo-continuous ASL (te-pCASL) with single-voxel point-resolved spectroscopy (PRESS) readout to quantify WM cerebral perfusion in a more time-efficient manner. Results are compared with te-pCASL with a conventional EPI readout for both WM and GM perfusion measurements. Perfusion measurements by te-pCASL PRESS and conventional EPI showed no significant difference for quantitative WM CBF values (Student's t-test, p = 0.19) or temporal SNR (p = 0.33 and p = 0.81 for GM and WM, respectively), whereas GM CBF values (p = 0.016) were higher using PRESS than EPI readout. WM CBF values were found to be 18.2 ± 7.6 mL/100 g/min (PRESS) and 12.5 ± 5.5 mL/100 g/min (EPI), whereas GM CBF values were found to be 77.1 ± 11.2 mL/100 g/min (PRESS) and 53.6 ± 9.6 mL/100 g/min (EPI). This study demonstrates the feasibility of te-pCASL PRESS for the quantification of WM perfusion changes in a highly time-efficient manner, but it does not result in improved temporal SNR, as does traditional te-pCASL EPI, which remains the preferred option because of its flexibility in use.
Assuntos
Encéfalo/diagnóstico por imagem , Encéfalo/fisiologia , Circulação Cerebrovascular/fisiologia , Angiografia por Ressonância Magnética/métodos , Processamento de Sinais Assistido por Computador , Substância Branca/diagnóstico por imagem , Substância Branca/fisiologia , Algoritmos , Velocidade do Fluxo Sanguíneo/fisiologia , Encéfalo/irrigação sanguínea , Humanos , Aumento da Imagem/métodos , Interpretação de Imagem Assistida por Computador/métodos , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , Marcadores de Spin , Substância Branca/irrigação sanguíneaRESUMO
AIM: The aim of this study was to assess biochemical changes in the brain of patients with hemiplegic migraine in between attacks. METHODS: Eighteen patients with hemiplegic migraine (M:F, 7:11; age 38 ± 14 years) of whom eight had a known familial hemiplegic migraine (FHM) mutation (five in the CACNA1A gene (FHM1), three in the ATP1A2 gene (FHM2)) and 19 age- and sex-matched healthy controls (M:F, 7:12; mean age 38 ± 12 years) were studied. We used single-voxel 7 tesla (1)H-MRS (STEAM, TR/TM/TE = 2000/19/21 ms) to investigate four brain regions in between attacks: cerebellum, hypothalamus, occipital lobe, and pons. RESULTS: Patients with hemiplegic migraine showed a significantly lower total N-acetylaspartate/total creatine ratio (tNAA/tCre) in the cerebellum (median 0.73, range 0.59-1.03) than healthy controls (median 0.79, range (0.67-0.95); p = 0.02). In FHM1 patients with a CACNA1A mutation, the tNAA/tCre was lowest. DISCUSSION: We found a decreased cerebellar tNAA/tCre ratio that might serve as an early biomarker for neuronal dysfunction and/or loss. This is the first high-spectral resolution 7 tesla (1)H-MRS study of interictal biochemical brain changes in hemiplegic migraine patients.
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Encéfalo/metabolismo , Transtornos de Enxaqueca/metabolismo , Espectroscopia de Prótons por Ressonância Magnética/métodos , Adulto , Encéfalo/fisiopatologia , Química Encefálica , Feminino , Humanos , Processamento de Imagem Assistida por Computador , Imageamento por Ressonância Magnética , Masculino , Pessoa de Meia-Idade , Transtornos de Enxaqueca/fisiopatologia , Enxaqueca com Aura/metabolismo , Adulto JovemRESUMO
The longitudinal relaxation time of blood is a crucial parameter for quantification of cerebral blood flow by arterial spin labeling and is one of the main determinants of the signal-to-noise ratio of the resulting perfusion maps. Whereas at low and medium magnetic field strengths (B0), its in vivo value is well established; at ultra-high field, this is still uncertain. In this study, longitudinal relaxation time of blood in the sagittal sinus was measured at 1.5 T, 3 T, and 7 T. A nonselective inversion pulse preceding a Look-Locker echo planar imaging sequence was performed to obtain the inversion recovery curve of venous blood. The results showed that longitudinal relaxation time of blood at 7 T was â¼ 2.1 s which translates to an anticipated 33% gain in the signal-to-noise ratio in arterial spin labeling experiments due to T1 relaxation alone compared with 3 T. In addition, the linear relationship between longitudinal relaxation time of blood and B0 was confirmed.
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Determinação do Volume Sanguíneo/métodos , Volume Sanguíneo/fisiologia , Encéfalo/fisiologia , Circulação Cerebrovascular/fisiologia , Interpretação de Imagem Assistida por Computador/métodos , Angiografia por Ressonância Magnética/métodos , Adulto , Velocidade do Fluxo Sanguíneo/fisiologia , Encéfalo/anatomia & histologia , Feminino , Humanos , Masculino , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , Adulto JovemRESUMO
High permittivity "dielectric pads" have been shown to increase image quality at high magnetic fields in regions of low radiofrequency transmit efficiency. This article presents a series of electromagnetic simulations to determine the effects of pad size and geometry, relative permittivity value, as well as thickness on the transmit radiofrequency fields for neuroimaging at 7 T. For a 5-mm thick pad, there is virtually no effect on the transmit field for relative permittivity values lower than â¼90. Significant improvements are found for values between 90 and â¼180. If the relative permittivity is increased above â¼180 then areas of very low transmit efficiency are produced. For a 1-cm thick pad, the corresponding numbers are â¼60 and â¼120, respectively. Based upon the findings, a new material (barium titanate, relative permittivity â¼150) is used to produce thin (â¼5 mm) dielectric pads which can easily be placed within a standard receive head array. Experimental measurements of transmit sensitivities, as well as acquisition of T(2) - and T 2*-weighted images show the promise of this approach.
Assuntos
Compostos de Bário/química , Mapeamento Encefálico/métodos , Imageamento por Ressonância Magnética/métodos , Neuroimagem/métodos , Titânio/química , Simulação por Computador , Humanos , Aumento da Imagem/métodos , Imageamento Tridimensional , Naftalenossulfonatos/química , Imagens de FantasmasRESUMO
Flow-territory mapping by MR imaging ASL noninvasively provides a unique insight into the distribution of cerebral perfusion. The introduction of planning-free vessel-encoded pCASL made flow-territory mapping feasible for clinical use, though lack of individual planning could impede reproducibility of this technique. We assessed the reproducibility of planning-free vessel-encoded pCASL in patients and controls. Results indicated that planning-free vessel-encoded pCASL is a reproducible method that could assist in clinical decision-making.
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Estenose das Carótidas/diagnóstico , Angiografia por Ressonância Magnética/métodos , Adulto , Artérias , Feminino , Humanos , Aumento da Imagem , Masculino , Pessoa de Meia-Idade , Reprodutibilidade dos TestesRESUMO
The intrinsic nonuniformities in the transmit radiofrequency field from standard quadrature volume resonators at high field are particularly problematic for localized MRS in areas such as the temporal lobe, where a low signal-to-noise ratio and poor metabolite quantification result from destructive B1⺠field interference, in addition to line broadening and signal loss from strong susceptibility gradients. MRS of the temporal lobe has been performed in a number of neurodegenerative diseases at clinical fields, but a relatively low signal-to-noise ratio has prevented the reliable quantification of, for example, glutamate and glutamine, which are thought to play a key role in disease progression. Using a recently developed high-dielectric-constant material placed around the head, localized MRS of the medial temporal lobe using the stimulated echo acquisition mode sequence was acquired at 7 T. The presence of the material increased the signal-to-noise ratio of MRS by a factor of two without significantly reducing the sensitivity in other areas of the brain, as shown by the measured B1⺠maps. An increase in the receive sensitivity B1⻠was also measured close to the pads. The spectral linewidth of the unsuppressed water peak within the voxel of interest was reduced slightly by the introduction of the dielectric pads (although not to a statistically significant degree), a result confirmed by using a pad composed of lipid. Using LCmodel for quantitative analysis of metabolite concentrations, the increase in signal-to-noise ratio and the slight decrease in spectral linewidth contributed to statistically significant reductions in the Cramer-Rao lower bounds (CRLBs), also allowing the levels of glutamate and glutamine to be quantified with CRLBs below 20%.
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Espectroscopia de Ressonância Magnética/instrumentação , Espectroscopia de Ressonância Magnética/métodos , Lobo Temporal/anatomia & histologia , Lobo Temporal/metabolismo , Adulto , Humanos , Pessoa de Meia-Idade , Adulto JovemRESUMO
We describe the design and testing of a quadrature transmit, eight-channel receive array RF coil configuration for the acquisition of images of the entire human spinal column at 7 T. Imaging parameters were selected to enable data acquisition in a clinically relevant scan time. Large field-of-view (FOV) scanning enabled sagittal imaging of the spine in two or three-stations, depending upon the height of the volunteer, with a total scan time of between 10 and 15 min. A total of 10 volunteers have been scanned, with results presented for the three subjects spanning the range of heights and weights, namely one female (1.6 m, 50 kg), one average male (1.8 m, 70 kg), and one large male (1.9 m, 100 kg).
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Coluna Vertebral/anatomia & histologia , Adulto , Simulação por Computador , Interpretação Estatística de Dados , Campos Eletromagnéticos , Feminino , Humanos , Aumento da Imagem , Masculino , Osteocondrose/patologia , Imagens de Fantasmas , Ondas de Rádio , Coluna Vertebral/patologia , Imagem Corporal TotalRESUMO
INTRODUCTION AND PURPOSE: Functional proton magnetic resonance spectroscopy (MRS) can be applied to measure pharmacodynamic effects of central nervous system (CNS)-active drugs. The serotonin precursor 5-hydroxytryptophan (5-HTP), administered together with carbidopa and granisetron to improve kinetics and reduce adverse effects, acutely enhances central serotonergic neurotransmission and induces hypothalamus-pituitary-adrenal-(HPA) axis activation. We studied the hypothalamic levels of glutamate/glutamine (Glx), choline (Chol), N-acetyl-aspartate (NAA) and creatine using 7-Tesla (7T) MRS, and adrenocorticotropic hormone (ACTH) and cortisol in peripheral blood, after the administration of the 5-HTP function test in healthy volunteers. METHODS: A randomized, double blind, placebo-controlled, two-way cross-over study was performed in 12 healthy males with a 7day wash-out period. After administration of the oral 5-HTP function test, ACTH and cortisol were measured over 4h and MRS scans at 7T were performed every 30min over 3h measuring Glx:Creatine, Chol:Creatine and NAA:Creatine ratios. RESULTS: In the hypothalamus, the administration of 5-HTP had no effect on the average Glx, Chol or NAA levels over 180min but induced a significant decrease of Glx at 60min on post-hoc analysis. 5-HTP-induced significant ACTH release reaching an E(max) of 60.2ng/L at 80min followed by cortisol with an E(max) of 246.4ng/mL at 110min. CONCLUSIONS: The reduction in hypothalamic Glx levels after serotonergic stimulation is compatible with activation of excitatory neurons in this region, which is expected to cause depletion of local glutamate stores. The hypothalamic MRS-response reached its maximum prior to subsequent increases of ACTH and cortisol, which support the functional relevance of hypothalamic Glx-depletion for activation of the HPA-axis. This exploratory study shows that MRS is capable of detecting neuronal activation following functional stimulation of a targeted brain area.
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5-Hidroxitriptofano/farmacologia , Ácido Glutâmico/efeitos dos fármacos , Hipotálamo/efeitos dos fármacos , Hipotálamo/metabolismo , Espectroscopia de Ressonância Magnética , Serotoninérgicos/farmacologia , Hormônio Adrenocorticotrópico/sangue , Adulto , Ácido Aspártico/análogos & derivados , Ácido Aspártico/metabolismo , Carbidopa/farmacologia , Colina/metabolismo , Dopaminérgicos/farmacologia , Método Duplo-Cego , Glutamina/metabolismo , Granisetron/farmacologia , Humanos , Masculino , Projetos Piloto , Fatores de Tempo , Adulto JovemRESUMO
BACKGROUND AND PURPOSE: Postoperative imaging of cochlear implants (CIs) needs to provide detailed information on localization of the electrode array. We evaluated visualization of a HiFocus1J array and accuracy of measurements of electrode positions for acquisitions with 64-section CT scanners of 4 major CT systems (Toshiba Aquilion-64, Philips Brilliance-64, GE LightSpeed-64, and Siemens Sensation-64). MATERIALS AND METHODS: An implanted human cadaver temporal bone, a polymethylmethacrylate (PMMA) phantom containing a CI, and a point spread function (PSF) phantom were scanned. In the human cadaver temporal bone, the visibility of cochlear structures and electrode array were assessed by using a visual analog scale (VAS). Statistical analysis was performed with a paired 2-tailed Student t test with significant level set to .008 after Bonferroni correction. Distinction of individual electrode contacts was quantitatively evaluated. Quantitative assessment of electrode contact positions was achieved with the PMMA phantom by measurement of the displacement. In addition, PSF was measured to evaluate spatial resolution performance of the CT scanners. RESULTS: VAS scores were significantly lower for Brilliance-64 and LightSpeed-64 compared with Aquilion-64 and Sensation-64. Displacement of electrode contacts ranged from 0.05 to 0.14 mm on Aquilion-64, 0.07 to 0.16 mm on Brilliance-64, 0.07 to 0.61 mm on LightSpeed-64, and 0.03 to 0.13 mm on Sensation-64. PSF measurements show an in-plane and longitudinal resolution varying from 0.48 to 0.68 mm and 0.70 to 0.98 mm, respectively, over the 4 scanners. CONCLUSION: According to PSF results, electrode contacts of the studied CI can be visualized separately on all of the studied scanners unless curvature causes intercontact spacing narrowing. Assessment of visibility of CI and electrode contact positions, however, varies between scanners.
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Implantes Cocleares , Processamento de Imagem Assistida por Computador , Imagens de Fantasmas , Complicações Pós-Operatórias/diagnóstico por imagem , Tomografia Computadorizada Espiral , Cadáver , Cóclea/diagnóstico por imagem , Eletrodos Implantados , Análise de Falha de Equipamento , Humanos , Medição da Dor , Ajuste de Prótese , Sensibilidade e Especificidade , Osso Temporal/diagnóstico por imagemRESUMO
Patient dose is usually estimated for a single radiographic projection or computed tomography (CT) series. In this study, patient dose was calculated for predefined clinical indications (24 radiography, 11 CT). Members of the radiology staff of each of 11 hospitals were trained in dose measurement and calculation techniques. Based on clinical indications participants decided on imaging protocols and calculated cumulative effective dose for a complete examination. Effective dose ranged from <1 microSv to 0.6 mSv for examinations with radiographs and from 0.2 to 12 mSv for CT scans. Differences in the imaging protocols contributedd to a substantial variation in patient dose. For mammography, average glandular dose (AGD) was estimated for 32-, 53- and 90-mm compressed breast thicknesses, with a median value of 0.74, 1.74 and 3.40 mGy, respectively. The results presented here demonstrate that a pragmatic choice of dosimetry methods enables local staff to estimate effective dose. The inclusion of imaging protocols in the dose surveys provided a broader view on the variations in patient dose between hospitals.
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Fluoroscopia , Mamografia , Imagens de Fantasmas , Radiografia , Serviço Hospitalar de Radiologia/normas , Radiometria/instrumentação , Processamento de Sinais Assistido por Computador/instrumentação , Tomografia Computadorizada por Raios X , Fluoroscopia/normas , Hospitais Gerais , Hospitais de Ensino , Hospitais Universitários , Humanos , Mamografia/normas , Imagens de Fantasmas/normas , Monitoramento de Radiação/normas , Radiografia/normas , Radiometria/normas , Espalhamento de Radiação , Software , Tomografia Computadorizada por Raios X/normasRESUMO
OBJECT: 1. Identify sources of variation affecting Magnetisation Transfer Ratio (MTR) histogram reproducibility between-centres. 2. Demonstrate complete elimination of inter-centre difference. MATERIALS AND METHODS: Six principle sources of variation were summarised and analysed. These are: the imager coil used for radiofrequency (RF) transmission, imager stability, the shape and other parameters describing the Magnetisation Transfer (MT) pulse, the MT sequence used (including its parameters), the image segmentation methodology, and the histogram generation technique. Transmit field nonuniformity and B1 errors are often the largest factors. PLUMB (Peak Location Uniformity in MTR histograms of the Brain) plots are a convenient way of visualising differences. Five multi-centres studies were undertaken to investigate and minimise differences. RESULTS: Transmission using a body coil, with a close-fitting array of surface coils for reception, gave the best uniformity. Differences between two centres, having MR imagers from different manufacturers, were completely eliminated by using body coil excitation, making a small adjustment to the MT pulse flip angle, and carrying out segmentation at a single centre. Histograms and their peak location and height values were indistinguishable. CONCLUSIONS: Body coil excitation is preferred for multi-centre studies. Analysis (segmentation and histogram generation) should ideally be carried out at a single site.
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Encéfalo/patologia , Imageamento por Ressonância Magnética/instrumentação , Imageamento por Ressonância Magnética/métodos , Magnetismo , Artefatos , Mapeamento Encefálico , Corpo Humano , Humanos , Interpretação de Imagem Assistida por Computador , Processamento de Imagem Assistida por Computador , Imageamento Tridimensional , Estudos Multicêntricos como Assunto , Ondas de Rádio , Reprodutibilidade dos Testes , Processamento de Sinais Assistido por ComputadorRESUMO
Patient and staff dose during CT guided coagulation of osteoid osteoma, tissue biopsy and abscess drainage were evaluated retrospectively on a conventional CT scanner and prospectively on a scanner equipped with fluoroscopic CT. The computed tomography dose index (CTDI) and the individual dose equivalent, i.e. the penetrating dose for workers at a depth of 10 mm tissue, were measured. Evaluation of CTDI enabled effective dose and maximum skin entrance doses for the patient to be determined. Doses were assessed for 96 CT guided interventions, including 16 drainages with average effective doses of 13.5 mSv and 9.3 mSv for the conventional CT scanner and the scanner with spiral CT fluoroscopy, respectively, 49 biopsies (effective doses of 8 mSv and 6.1 mSv, respectively), and 31 coagulations of osteoid osteoma (effective doses of 2.1 mSv and 0.8 mSv, respectively). Effective doses to patients were in the same range as those observed for regular diagnostic CT examinations. Entrance skin doses were well below the 2 Gy threshold for deterministic skin effects on the CT scanner equipped with fluoroscopic function (0.03-0.33 Gy), whilst skin doses on the conventional scanner were considerably higher (0.09-1.61 Gy). This is mainly owing to the fact that on the conventional scanner mAs was rarely reduced for scans evaluating needle position whereas low mAs per rotation was selected on the scanner with the fluoroscopy option. The maximum dose to a worker measured outside the lead apron was 28 microSv for one single procedure. The mean dose per procedure was below 10 microSv for radiologists and below 1 microSv for radiographers. Correcting for attenuation of the lead apron, the doses to workers are very low.
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Exposição Ocupacional , Doses de Radiação , Radiografia Intervencionista , Tomografia Computadorizada por Raios X , Biópsia , Neoplasias Ósseas/diagnóstico por imagem , Neoplasias Ósseas/cirurgia , Drenagem , Eletrocoagulação , Fluoroscopia , Humanos , Osteoma Osteoide/diagnóstico por imagem , Osteoma Osteoide/cirurgia , Radiometria/métodos , Estudos RetrospectivosRESUMO
The objective of this study was to derive the effective dose to patients from examinations of the upper gastrointestinal (GI) tract at 11 X-ray units in 10 Dutch hospitals. Entrance dose and entrance dose rate were measured at the surface of a homogeneous PMMA phantom and at the entrance surface of the image intensifier. Dose-area products (DAPs) were assessed during examinations of patients. The patients (334 females and 256 males) ages were 18-95 years (average 52 years). Effective dose was assessed from DAP using Monte Carlo computer calculations for male and female mathematical anthropomorphic phantoms. The DAPs measured during the survey showed substantial variations, i.e. an overall average value of 21 Gy cm2 and a range of average DAP per X-ray unit varying from 7 to 56 Gy cm2. Variations in the number of images (8-28) and the fluoroscopy time (1.7 min-7.0 min) were also large. A DAP to effective dose conversion factor of 0.32 mSv Gy cm-2 was derived for upper GI studies. The dose survey yielded an overall average effective dose of 6.7 mSv. At one location an examination involving as many as 28 projections was performed, whilst maintaining a DAP well below 15 Gy cm2 and an effective dose below 6 mSv. This was achieved using modern equipment (i.e. high frequency generator, digital spot films) with 0.2 mm additional copper filtration and a relatively high tube voltage. For examinations of the upper GI tract, the application of a reference value of 30 Gy cm2 for the DAP will ensure that, in general, the effective dose to individual patients will not exceed 15 mSv.
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Sistema Digestório/diagnóstico por imagem , Doses de Radiação , Intensificação de Imagem Radiográfica , Adolescente , Adulto , Idoso , Idoso de 80 Anos ou mais , Sulfato de Bário , Meios de Contraste , Duodeno/diagnóstico por imagem , Esôfago/diagnóstico por imagem , Feminino , Fluoroscopia , Humanos , Masculino , Pessoa de Meia-Idade , Radiometria/métodos , Estômago/diagnóstico por imagemRESUMO
PURPOSE: To determine the effective dose to the patient during radiographic colon examination. MATERIALS AND METHODS: The integral dose-area product was measured during colon examination in 1,733 patients aged 18-94 years. The effective dose was estimated from the dose-area product through computer simulations of radiation transport in anthropomorphic phantoms. The relation between patient dose and imaging or radiographic technique was considered. Patient dose from a biphasic colon examination was compared to that from a double-contrast examination. RESULTS: The factors for converting dose-area product to effective dose were 0.29 mSv x Gy(-1) x cm(-2) and 0.27 mSv x Gy(-1) x cm(-2) for the biphasic and the double-contrast studies, respectively. The average dose-area product for the biphasic colon examination was 21 Gy x cm2, of which 13 Gy x cm2 was attributed to the double-contrast views. The average dose-area product was 29 Gy x cm2 (range, 18-53 Gy x cm2); the average effective dose was 4.7 mSv (range, 2.7-8.4 mSv). CONCLUSION: Careful selection of the radiologic technique resulted in a surprisingly low dose during the biphasic colon examination. It is recommended that additional filtration of at least 0.1-mm copper be applied and that a screen-film combination with a speed class of at least 400 be used. Dose reduction when using digital techniques is often not realized in clinical practice.