Métodos de Imagem em Neurorradiologia

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Métodos de Imagem 
em Neurorradiologia 
Tomografia e Ressonância Magnética 
Aplicações clínicas 
OPÇÕES ATUAIS 
DE 
NEUROIMAGEM 
• RM padrão: T1WI, T2W2, FLAIR e/ou DP. Pode complementar-se com 
T1C+. 
• TCA revisada com janelas cerebrais e ósseas. Pode ser suplementada por 
TCC+. 
• TC: doenças agudas 
• RM: doenças subagudas e crônicos. 
TOMOGRAFIA 
COMPUTADORIZ
ADA 
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RESSONÂNCIA 
MAGNÉTICA 
Ressonância Magnética 
• fluids – cerebrospinal fluid (CSF), synovial fluid, oedema; 
• water-based tissues – muscle, brain, cartilage, kidney; 
• fat-based tissues – fat, bone marrow. 
Pulso de Eco de Spin 
• The spin echo pulse sequence is the most commonly used pulse 
sequence. The pulse sequence timing can be adjusted to give T1-
weighted, Proton or spin density, and T2-weighted images. Dual echo 
and multiecho sequences can be used to obtain both proton density and 
T2-weighted images simultaneously. 
• The two variables of interest in spin echo sequences is the repetition time 
(TR) and the echo time (TE). All spin echo sequences include a slice 
selective 90 degree pulse followed by one or more 180 degree refocusing 
pulses as shown in the diagram. 
 
• T1/T2/DP 
 
Física do Spin Echo 
• Fat quickly realigns its longitudinal magnetization with B0, and it 
therefore appears bright on a T1 weighted image. Conversely, water has 
much slower longitudinal magnetization realignment after an RF pulse, 
and therefore has less transverse magnetization after a RF pulse. Thus, 
water has low signal and appears dark. 
• If T1WIs did not have short TRs, then all the protons would recover their 
alignment with the main magnetic field and the image would be 
uniformly intense. Selecting a TR shorter than than tissues' recovery time 
allows one to differentiate them (i.e. tissue contrast). 
• T1-weighted sequences provide the best contrast for paramagnetic 
contrast agents (e.g. a gadolinium-containing compounds). 
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Física do Spin Echo 
• The amount of T2 decay a tissue experiences depends on multiple 
factors. Each tissue has an inherent T2 value, but external factors (such 
as magnetic field inhomogeneity) can increase the T2 relaxation time. 
This additional effect is captured in T2*. The refocusing pulse in spin-
echo sequences helps to mitigate these extraneous influences on the T2 
relaxation time, trying to keep the image T2 weighted rather than T2* 
weighted. 
Contraste 
• T1: Cerebrospinal fluid is dark. T1 weighting is useful for visualizing 
normal anatomy. 
• T2: CSF is light, but fat (and thus white matter) is darker than with T1. 
T2 is useful for visualizing pathology. 
• PD (proton density): CSF has a relatively high level of protons, making 
CSF appear bright. Gray matter is brighter than white matter. 
Single midline 
sagittal T1 
weighted 
image 
demonstrates 
normal 
anatomy, 
including the 
posterior 
pituitary bright 
spot. 
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Coronal T2 MRI 4 
 
Axial T2 MRI Axial PD MRI 
Pulso de Gradiente de Eco 
• Images from other gradient echo sequences such as GRASS and FISP have less 
intuitive tissue contrast characteristics than FLASH. The FLASH and SPGR 
sequences show better tissue contrast between white matter and grey matter in the 
brain and spinal cord than GRASS or FISP and are preferred when the time of 
acquisition does not have to be very short. GRASS and FISP maintain better SNR 
than FLASH at short TR times and are therefore preferred with breath-holding 
techniques, for example. 
 
• T1/T2(T2*) 
T2 Star 
• T2* is useful to detect bleeding within infarction. As hemosiderin (blood 
product) creates susceptability artefact, its detection requires T2* or more 
recent SWI. Mass effect and hemorrhagic transformation usually occur in 
subacute infarction. 
Haemorrhagic 
cerebral 
infarction 
T2* images show 
hypointense area 
of hemosiderine 
deposition within 
the lesion. Mild 
compression of 
ipsilateral lateral 
ventricle is 
noted. 
 
Haemorrhagic 
cerebral 
infarction 
T2* images show 
hypointense area 
of hemosiderine 
deposition within 
the lesion. Mild 
compression of 
ipsilateral lateral 
ventricle is 
noted. 
 
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Pulso de Recuperação de Inversão 
• Variação do Spin Echo 
• Inversion recovery pulse sequences are used to give heavy T1-weighting. The basic part of an 
inversion recovery sequence is a 180 degree RF pulse that inverts the magnetization followed by a 90 
degree RF pulse that brings the residual longitudinal magnetization into the x-y or transverse plane 
where it can be detected by an RF coil. 
• In imaging, the signal is usually refocused with a 180 degree pulse as in a spin echo sequence.The 
time between the initial 180 degree pulse and the 90 degree pulse is the inversion time (TI). A diagram 
of the sequence is shown to the right. 
 
• STIR/FLAIR 
Pulso de atenuação de fluído com inversão 
de recuperação (FLAIR) 
• Usa grande T1 para remover efeitos de fluidos das imagens. 
• É ajustado para tempo de relaxamento do componente que irá ser suprimido. O tempo de 
inversão para supressão de fluido (T1 longo) é definido ocmo zero, apagando o sinal da 
imagem. 
• Isso permite a detecção de mudanças súbitas na periferia dos hemisférios e em regiões 
periventriculares próximas ao LCR. 
• É útil em avaliação de doenças do SNC, como: 
– Infarto; 
– Esclerose Múltipla; 
– Hemorragia Subaracnoidea; 
– Ferimentos cranianos e outros. 
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Imagem Ponderada em Difusão (DWI) 
• Forma de IRM baseado na medida do movimento browniano das moléculas de 
água em um volume de tecido. A relação entre histologia e difusão é complexa, 
entretando geralmente, tecidos densamente celularizados exibem menores 
coeficientes de difusão, assim a DWI é útil para caracterizar tumores e isquemia 
cerebral. 
 
• ADC/DTI 
Imagem Ponderada em Difusão (DWI) 
• DW imaging has a major role in the following clinical situations : 
– early identification of ischemic stroke 
– differentiation of acute from chronic stroke 
– differentiation of acute stroke from other stroke mimics 
– differentiation of epidermoid cyst from arachnoid cyst 
– ‘differentiation of abscess from necrotic tumors 
– assessment of cortical lesions in CJD 
– differentiation of herpes encephalitis from diffuse temporal gliomas 
– assessment of the extent of diffuse axonal injury 
– grading of gliomas and meningiomas (need further study) 
– assessment of active demyelination 
Lesions with intense high signal 
• acute ischaemia 
• meningiomas 
• abscess 
• empyema 
• cytotoxic cerebral oedema 
• chordoma 
• intracranial epidermoid cyst 
• CJD 
Lesions with variable or moderately high 
signal 
• primary central nervous system vasculitis 
• primary central nervous system lymphoma (PCNSL) 
• haemangiopericytoma 
• CADASIL 
• primitive neuroectodermal tumour (PNET) 
• meningiomas 
• medulloblastoma 
• intracranial germinoma 
• pineoblastoma 
• choroid plexus cyst 
• x linked adrenoleukodystrophy 
• kuru 
• carbon monoxide poisoning 
• methanol poisoning 
• Wernicke encephalopathy 
• hyperammonemia 
• deep cerebral vein thrombosis 
• canavan disease 
• japanese encephalitis 
• inborn errors of metabolism like: 
– maple syrup urine disease 
– nonketotic hyperglycemia 
– methyle malonic aciduria 
– gluteric aciduria type I 
– Wilson's disease 
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Sporadic Creutzfeldt–Jakobdisease 
Creutzfeldt-Jakob disease 
(CJD) is a spongiform 
encephalopathy that results in 
a rapidly progressive 
dementia and other non-
specific neurological features. 
CJD is thought to be mediated 
via (infectious) prions, a type 
of protein. 
CJD leads to spongiform 
degeneration of the brain, 
which is thought to be caused 
by the conversion of normal 
prion protein to 
proteinaceous infectious 
particles that accumulate in 
and around neurons and lead 
to cell death. 
 
 
Coeficiente aparente de Difusão (ADC) 
• Apparent diffusion coefficient (ADC) is a measure of the magnitude of diffusion (of 
water molecules) within tissue, and is commonly clinically calculated using MRI with 
diffusion weighted imaging (DWI). 
• Diffusion-weighted imaging (DWI) is widely appreciated as an indispensable tool in 
the examination of the CNS. It is considered useful not only for the detection of acute 
ischaemic stroke but also for the characterization and differentiation of brain tumors 
and intracranial infections. 
ADC 
Mild 
Ventriculomegaly. 
Restriction on 
diffusion in the 
periventricular 
region along 
bilateral lateral 
ventricles. Minimal 
ependymal 
enhancement on 
contrast 
administration. MRI 
features likely 
representing 
ventriculitis. 
There are muliple bilateral near symmetrical foci of restriced diffuion (appearing hyperintense on DWI 
with corresponding ADC imges showing dark signal) seen in both cerebral hemispheres seen involving the 
deep white matter and sub-cortical white matter.[1] There is no perilesional oedema. No large territorial 
infarctions. No gyral swelling or sulcal effacement. DWI / ADC : b1000, TR - 5600; TE 98; 3T Siemens Skyra 
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Imagem de Tensor de Difusão (DTI) 
• Diffusion tensor imaging is an extension of diffusion weighted imaging (DWI) 
that allows data profiling based upon white matter tract orientation 
• DWI is based on the measurement of brownian motion of water molecules. This 
motion is restricted by membranous boundaries. In white matter, diffusion 
follows the 'pathway of least resistance' along the white matter tract; this 
direction of maximum diffusivity along the white-matter fibers is projected into 
the final image. 
 
Usos clínicos 
• assess the deformation of white matter by tumors - deviation, infiltration, 
destruction of white matter 
• delineate the anatomy of immature brains 
• pre-surgical planning 
• Alzheimer disease - detection of early disease 
• schizophrenia 
• focal cortical dysplasia 
• multiple sclerosis - plaque assessment 
 
Caso - Mulitple sclerosis by diffusion 
tensor imaging 
• Multiple sclerosis (MS) is a relatively common acquired chronic relapsing demyelinating disease 
involving the central nervous system. It is by definition disseminated not only in space (i.e multiple 
lesions), but also in time (i.e. lesions are of different age). 
• MS is believed to result from a cellular mediated autoimmune response against ones own myelin 
components, with loss of oligodendrocytes, with little or no axonal degeneration. 
 
• Demyelinating plaques cause destruction of white matter fibers which is manifested in DTI as 
increased diffusivity of water molecules. This can be demostrated by comparing FA and ADC values at 
the plaque site, normal appearing white matter (which may be affected but to less degree) and far 
normal appearing white matter. Tractography can illustrate the affected white matter tract. 
• FA and ADC values can be used in follow up of the patient. 
 
Mulitple sclerosis 
by diffusion tensor 
imaging 
 
Tractography 
Tractography of the 
forceps minor fibers 
and fronto-occipital 
fasciculus reveals 
white matter 
disruption at the 
site of the plaque. 
Diffusion-tensor MRI imaging and fiber 
tractography 
• Diffusion-tensor imaging (DTI) is a MRI technique that uses anisotropic diffusion to estimate the 
axonal (white matter) organisation of the brain. 
• Fiber tractography (FT)is a 3D reconstruction technique to access neural tracts using data collected 
by DTI. 
• Within cerebral white matter, water molecules tend to diffuse more freely along the direction of axonal 
fascicles than across them. Such directional dependence of diffusivity is termed anisotropy. 
 
 
– red for fibres crossing from left to right 
– green for fibres traversing in antero-posterior direction 
– blue for fibres going from superior to inferior 
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Imagem Ponderada em Susceptibilidade 
(SWI) 
• Susceptibility weighted imaging (SWI) is an MRI sequence which 
is particularly sensitive to compounds which distort the local magnetic field and 
as such make it useful in detecting blood products, calcium etc... 
• The most common use of susceptibility weighted imaging (SWI) is for the 
identification of small amounts of haemorrhage / blood product or calcium, both 
of which may be inapparent on other MRI sequences. 
Diffuse axonal injury in trauma. GRE image above; SWI image below. Data was collected 
on a 1.5-tesla scanner (Vision, Siemens Medical Solutions) with a TE = 40 msec and a 
resolution of 0.5 mm x 1.0 mm by 2.0 mm. Images courtesy of Dr. Karen Tong, Loma Linda 
University. 
http://www.auntminnie.com/index.aspx?sec=ser&sub=def&pag=dis&ItemID=62958 
Perfusion weighted imaging (PWI) 
• Perfusion weighted imaging is a term used to denote a variety of MRI 
techniques able to give insights into the perfusion of tissues by blood. 
• The main role of perfusion imaging is in evaluation of ischaemic conditions (e.g. 
acute cerebral infarction to determine ischaemic penumbra, moya-moya disease 
to identify vascular reserve) and neoplasms (e.g. identify highest grade 
component of diffuse astrocytomas, help distinguish glioblastomas form cerebral 
metastases). 
Caso 
• MRI of hyperacute stroke at 2 hours postictus. The T2-weighted image is normal. 
• The FLAIR image shows hyperintense vessels (HVS - see text) in the territory of the middle carotid artery (MCA) 
(arrow), consistent with slow arterial flow, but the FLAIR shows no tissue abnormality. 
• Diffusion-weighted imaging (DWI) shows hyperintensity in the deep middle cerebral artery territory consistent with 
cytotoxic edema in an acute stroke (arrow), but there is no evidence of cortical ischemia. 
• Perfusion-weighted imaging (PWI) (time-to-peak image) shows reduced perfusion in the full (cortical and 
subcortical) MCA territory. This suggests a much larger area of tissue at risk than shown by DWI or 
conventional images. This is known as a diffusion-perfusion mismatch (see text). Some areas of reduced 
perfusion show HVS on FLAIR whereas others do not. 
• Three-dimensional time-of-flight magnetic resonance angiography (MRA) confirms a proximal MCA occlusion or 
severe stenosis. 
ACA – Azul 
ACP – Amarelo 
ACM - Vermelho 
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Espectroscopia associada à RM (ERM) 
• Mostra a distribuição dos metabólitos cerebrais baseado no desvio 
químico dos prótons em seu interior. 
• Três metabólitos importantes: colina (marcador de membranas celulares 
 densidade celular); N-acetil-aspartato (NAA  marcador de 
densidade neuronal); creatina (uniformemente distribuído  padrão de 
referência) 
Colina 
• Colina pode ser considerada um marcador tumoral. Se elevar a razão 
colina/creatina, pode-se diferenciar a necrose por radiação do tumor 
recorrente ou infecção. 
• Também permite a graduação de tumores: o local com a maior razão 
reflete melhor o grau histológico do tumor. 
• Picos altos de colina são sugestivos de meningioma. 
N-acetil-aspartato (NAA) 
• Redução da NAA/creatina é encontrada em condições de morte neuronal.• Diminução focal é encontrada em esclerose temporal mesial e infartos. 
• Depleção global sugere esclerose múltipla e doenças demenciais (p. ex.: 
Alzheimer) 
Valores 
• lactate peak: resonates at 1.3 ppm 
• lipid peak: resonates at 1.3 ppm 
• alanine peak: resonates at 1.48 ppm 
• N-acetylaspartate (NAA) peak: resonates at 2.0 
• glutamine / glutamate peak: resonate sat 2.2-2.4 ppm 
• GABA peak: resonates at 2.2-2.4 ppm 
• citrate peak: resonates 2.6 ppm 
• creatine peak: resonates at 3.0 ppm 
• choline peak: resonates at 3.2 ppm 
• myo-inositol peak: resonates at 3.5 ppm 
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Canavan disease, also known 
as spongiform degeneration of 
white matter is a leukodystrophy 
(dysmyelinating disorders) 
clinically characterised by 
megalocephaly, severe mental 
deficits and blindness. 
MRS reveals a grossly raised NAA peak, this has 
been described only in cases of Canavan's disease 
and is fairly specific. 
IMAGEM 
FUNCIONAL 
Positron emission tomography (PET) 
• Positron emission tomography (PET) is a modern non-invasive imaging technique for quantification 
of radioactivity in vivo. It involves the use of a radiopharmaceutical injected into the body and its 
accumulation in the body is detected, quantified and interpreted. 
• Radionuclides (which are labelled to the FDG) decay in the body with the release of a positron, i.e. a 
beta particle. The beta particle travels a short distance and annihilates with an anti-particle (electron). 
The annihilation reaction results in the formation of two high energy photons which travel in opposite 
directions. 
• Each photon has an energy of 511 keV. These two photons travelling in opposite directions are detected 
by two detectors at opposite ends facing each other and the radioactivity is localised somewhere along 
a line between the two detectors. This is the line of response. 
Positron emission tomography (PET) 
• neurologic 
– early diagnosis of Alzheimer's disease 
– localisation of seizure focus in interictal phase 
– localising eloquent areas (e.g. speech, motor function) 
SPECT vs PET 
• Positron emission tomography (PET) 
• very expensive 
• uses positron emitting radioisotope (tracer) 
– 18F 
• better contrast and spatial resolution 
• Single-photon emission computed tomography (SPECT) 
• lower cost 
• uses gamma emitting radioisotope (tracer) 
– technetium-99m 
– iodine-123 
– iodine-131 
• less contrast and spatial resolution (c.f. PET) 
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CT scan shows enlargement of cerebral sulci and loss of gyral volume associated with 
mild compensatory dilation of the ventricular system. This is perhaps most marked in the 
parietal regions. These are nonspecific findings that are sometimes found in the 
asymptomatic population in this age group. 
Usual pattern of radiopharmaceutical distribution in brain parenchyma. 
PET-CT uses radiolabeled glucose analogue FDG to measure glucose metabolism, which 
indicates levels of neurosynaptic activity. On these FDG PET images it`s seen decreased 
metabolism activity on bilateral parietotemporal cortex. 
PET-CT uses radiolabeled glucose analogue FDG to measure glucose metabolism, which 
indicates levels of neurosynaptic activity. On these FDG PET images it`s seen decreased 
metabolism activity on bilateral parietotemporal cortex. 
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FDG PET-CT images show decreased metabolism activity on bilateral parietotemporal 
cortex. 
Functional MRI 
• Functional magnetic resonance imaging (fMRI) is a technique used to obtain 
functional information by visualising cortical activity. fMRI detects subtle alteration 
in blood flow in response to stimuli or actions. It is used in two broad ways: 
• clinical practice 
– typically in pre-surgical patients 
– aimed at localizing eloquent areas (e.g. speech, motor function) 
• research 
– often cohort of patients (often normals) 
– aimed at elucidating novel neural networks 
fMRI image 
(BOLD 
imaging) of a 
patient 
performing 
bilateral 
finger motor 
tasks. Note 
the increased 
blood flow in 
the motor 
and adjacent 
sensory strip. 
Block design of a language 
task in a healthy subject. 
Regions of statistically 
significant activation. 
Referências 
• Gray, Henry. Gray’s Anatomy of the Human Body: Descriptive and Surgical. Octopus Publishing Group: London, 
2012. 
• BRANT, William E.; HELMS, Clyde A. (Ed.). Fundamentals of diagnostic radiology. Lippincott Williams & 
Wilkins, 2012. 
• CONDER, GABRIEL; RENDLE, JOHN; MISRA, RAKESH R.; KIDD, SARAH. A–Z of Emergency Radiology. 
Cambridge University Press, 2009. 
• HOLMES, Erskine J.; MISRA, Rakesh R. AZ of emergency radiology. Cambridge University Press, 2004. 
• JUHL, John H.; CRUMMY, Andew B.; KUHLMAN, Janet E. Interpretação radiológica. Interpretação radiológica, 
2000. 
• SARTOR, Klaus. Brain Imaging (Direct Diagnosis in Radiology). Thieme, 2012. 
• GAILLARD, F. Appendicolith; Radiopaedia. org. 2015. 
• William Herring. LEARNING RADIOLOGY, 2015. 
 
ACHADOS 
NORMAIS EM 
IRM 
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• Pituitary region mass with intrinsic high T1 signal are relatively 
frequently encountered, and the presence of high T1 signal narrows the 
differential somewhat. 
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