Clinical imaging of cancer metastasis

Tumour imaging is an essential part of the practice of oncology, with a crucial role in screening programmes and in diagnosis and staging of established disease. Furthermore, the assessment of tumour size by imaging, usually with computer tomography (CT) scanning, is a key component in determining the tumour response to therapy both in clinical trials and in daily oncology practice. Techniques such as CT, ultrasound (US) and magnetic resonance imaging (MRI) provide high resolution anatomical images with detailed structural information. However, these imaging modalities yield limited functional information on the tumour tissues and often cannot distinguish residual disease from non-viable or necrotic tumour masses, nor can they detect minimal residual disease. In contrast, radiopharmaceutical imaging and, in particular, positron emission tomography (PET) can give some functional information about the underlying tissues. The possibility of refining these techniques and also the emergence of newer imaging modalities that can detect changes in cancers at the physiological, cellular or molecular levels, gives rise to the notion that these methods will have implications for drug development strategies and also future clinical management. In this review, we briefly discuss the current role of imaging in clinical practice, describe some of the advances in imaging modalities currently undergoing evaluation, and speculate on the future role of these techniques in developmental therapeutics programmes.     

IRM de perfusion,de perméabilité et morphologique : application en radiothérapie neuro-oncologique

There is no clear consensus for tumour volume definition in radiotherapy of brain tumours, particularly for high-grade gliomas (HGG). They are infiltrative and heterogeneous, sub-populations of low and high grade can coexist inside one tumour volume, and peritumoral oedema is partly due to a vasogenic mechanism but also to a microscopic extension of sparse tumour cells. All these characteristics are not directly detectable using a conventional MR imaging (MRI). Complementary to the anatomical sequences (T1/T2), still always mandatory, functional maps using the dynamic MRI with a T2* weighted sequence reflect micro-vessel perfusion and permeability, more on a quantitative aspect and a qualitative one, respectively. These parameters better appreciate neo-vascularity of gliomas and areas associated with a higher value of perfusion are clearly correlated with a higher grade. Even a low-grade glioma but with detectable areas of high permeability presents a two-fold risk of recurrence versus another one with the same anatomical characteristics and treatment, but without any micro-vascular leakage. for high-grade gliomas, a high level of tissue perfusion seems to be better predictive for the risk of recurrence than histology itself. The exact co-registration of anatomic and vascular maps is currently available in clinical practice and can be incorporated during the dedicated brain MRI for radiotherapy. Its potential for better predicting the exact sites of recurrence after treatment has to be prospectively evaluated and a strong interest for a dose-escalating study is evident. Finally, T2* dynamic MRI has the ability to differentiate post-treatment modifications from recurrence better than conventional imaging.     

磁共振成像对骨结核和骨肿瘤的诊断价值

目的探讨磁共振成像（MRI）对骨结核和骨肿瘤的诊断价值。方法收集2008年5月至2012年3月间拟诊断为骨结核的24例患者和24例骨肿瘤患者,所有患者均行MRI检查。结果骨结核与骨肿瘤的MRI表现多样,但是骨肿瘤的MRI诊断准确率明显高于骨结核（P〈0．05）。当b=150s／mm2时,骨结核与骨肿瘤的ADC值差异无统计学意义（P〉0．05）;而当b=300s／mm2时,骨肿瘤的ADC值明显低于骨结核的ADC值（P〈0．05）。结论MRI对于骨结核和骨肿瘤都有比较高的诊断价值,但是对骨肿瘤的诊断能提供更丰富的信息。     

The clinical importance of magnetic resonance imaging versus computed tomography in malignant pleural mesothelioma

There is no standard therapy for malignant pleural mesothelioma (MPM), but recent reports have shown that extensive surgery combined with chemo- and radiotherapy prolongs the survival of selected patients with early stage disease. This emphasises the need for accurate staging procedures at diagnosis and reliable imaging methods to assess response to treatment. Computed tomography (CT) of the chest has been the standard imaging method for these purposes for the last decade, but it is limited in its ability to demonstrate accurately the platelike growth pattern of MPM within the thorax due to the partial volume effect on curved surfaces. In order to define the value of magnetic resonance imaging (MRI) in the imaging of MPM, we have compared the findings from 26 parallel paired CT and MRI scans of mesothelioma patients at various stages of the disease. MRI showed tumour spread into the interlobar fissures, tumour invasion of the diaphragm and through the diaphragm, and invasion of bony structures better than CT. Invasion of the chest wall and mediastinal soft tissue and tumour growth into the lung parenchyma were equally well seen on both imaging methods. CT was better for detecting the inactive pleural calcifications. MRI is a sensitive detector of the characteristic growth pattern and extension of MPM and we recommend its use more widely for the clinical management of MPM especially when evaluating tumour resectability and in research protocols when an accurate evaluation of disease extent is essential.     

Computed Tomography–Magnetic Resonance Image Registration in Radiotherapy Treatment Planning

Magnetic resonance imaging (MRI) is being increasingly used in radiotherapy treatment planning (RTP). MRI has the potential to provide improved localisation of target volumes, leading to better tumour control rates and reduced normal tissue complications, due to capabilities including excellent soft-tissue discrimination and the ability to provide scans in which the image contrast is weighted according to different tissue properties. When computed tomography (CT)–MRI image registration is deployed, MR’s advantages are combined with CT’s geometrical security and its ability to provide electron density information. The quality of CT–MRI image registration can be favourably influenced by aspects of scan acquisition, including patient positioning/immobilisation and scan protocols. Appropriate protocols can ameliorate the possible presence of MR spatial distortions and other artefacts, but quality assurance of scanning remains essential. Here, the methods and quality assurance of CT–MR image registration are discussed. Developments in MRI scanner technology are progressively offering advantages for RTP, in terms of the possibility of better matching of patient positioning versus CT in a greater range of anatomical regions, while allowing thinner slices for better image quality in reformatted orthogonal planes.     

Clinical and anatomical guidelines in pelvic cancer contouring for radiotherapy treatment planning.

BACKGROUND AND PURPOSE: Many observations on potential inadequate coverage of tumour volume at risk in advanced cervical cancer (CC) when conventional radiation fields are used, have further substantiated by investigators using MRI, CT or lymphangiographic imaging. This work tries to obtain three dimensional margins by observing enlarged nodes in CT scans in order to improve pelvic nodal chains clinical target volumes (CTVs) drawing, and by looking for corroborative evidence in the literature for a better delineation of tumour CTV. METHOD: Eleven consecutive patients (seven males, four females, mean age 62 years, range 43-78) with CT diagnosis of nodal involvement caused by pathologically proved carcinoma of the cervix (n = 2), carcinoma of the rectum (n = 2), carcinoma of the prostate (n = 2), non-Hodgkin lymphoma (n = 2), Hodgkin lymphoma (n = 1), carcinoma of the penis (n = 1) and carcinoma of the corpus uteri (n = 1) were retrospectively reviewed. Sixty CT scans with 67 enlarged pelvic nodes were reviewed in order to record the more proximal structures (muscle, bone, vessels, cutis or subcutis and other organs) to each enlarged node or group of nodes according to the four surfaces (anterior, lateral, posterior and medial) in a clockwise direction. RESULTS: A summary of the observations of each nodal chain and the number of occurrences of every marginal structure on axial CT slices is presented. Finally, simple guidelines are proposed. CONCLUSIONS: Tumour CTV should be based on individual tumour anatomy-mainly for lateral beams as it results from sagittal T2 weighted MRI images. Boundaries of pelvic nodes CTVs can be derived from observations of enlarged lymph nodes in CT scans.     

髓母细胞瘤的CT和MRI影像学分析及临床意义

目的：通过对髓母细胞瘤的CT及MRI表现分析,加强对本病的认识,提高术前诊断的准确性并合理选择治疗方案。方法：对31例经手术、病理证实的髓母细胞瘤进行回顾性分析,所有病例均行CT和／或MRI检查。结果：髓母细胞瘤好发于儿童,常见于小脑蚓部;成人髓母细胞瘤少见,多见于小脑半球。CT平扫呈等或稍高密度影,增强扫描多强化明显。MRI扫描T1加权像呈低或等信号,T2加权像呈略高或混杂信号,增强扫描强化明显。结论：髓母细胞瘤有特定的发生部位、年龄及影像学特征性;仔细分析CT和MRI表现,可做出准确的术前诊断并指导制定治疗方案,改善预后。     

Comparison between Computer Tomography and Magnetic Resonance Imaging in the Diagnosis of Small Hepatocellular Carcinoma

Background: Hepatocellular carcinomas (HCCs) less than 2 cm in diameter generally demonstrate a good outcome after curative therapy. However, the diagnosis of small HCC can be problematic and requires one or more dynamic imaging modalities. This study aimed to compare the sensitivity and agreement between CT and MRI for the diagnosis of small HCCs. Methods: CT and/or MRI scans of HCCs (1-2 cm) diagnosed by histopathology or typical vascular pattern according to the 2005 AASLD criteria were blindly reviewed by an abdominal radiologist. The reports were defined as conclusive/typical when arterial enhancement and washout during the portal/delayed phases were observed and as inconclusive when typical vascular patterns were not observed. The sensitivity and Cohen’s kappa (k) for agreement were calculated. Results: In 27 patients, 27 HCC nodules (1-2 cm) were included. Diagnosis with a single-imaging modality (CT or MRI) was 81 % versus 48 % (p = 0.01). The CT sensitivity was significantly higher than MRI (78 % versus 52 %, p = 0.04). Among 27 nodules that underwent both CT and MRI, a discordance in typical enhancement patterns was found (k = 0.319, p = 0.05). In cases with inconclusive CT results, MRI gave only an additional 3.7 % sensitivity to reach a diagnosis. In contrast, further CT imaging following inconclusive MRI results gave an additional 29.6 % sensitivity.Conclusions: A single typical imaging modality is sufficient to diagnose small HCCs. Compared with MRI, multiphasic CT has a higher sensitivity. The limitations of MRI could be explained by the greater need for patient cooperation and the types of MRI contrast agent.     

Imaging in head and neck cancer

Opinion statement The goals of imaging in head and neck cancer are to establish tumor extent and size, to assess nodal disease, to evaluate for perineural tumor spread, and to distinguish recurrent tumor from post-treatment changes. MRI is the preferred modality for assessment of nasopharyngeal, sinonasal, and parotid tumors, because of better contrast resolution, high frequency of perineural spread, and less prominent motion artifacts. MRI is the best modality to delineate the extent of intraorbital and intracranial extension of malignant tumors. Tumors of the oropharynx, larynx, and hypopharynx are frequently primarily imaged with CT, which is less affected by breathing and swallowing artifacts. MRI is also the initial study of choice for tumors confined to the oral tongue, and possibly also for other oral cavity locations because MRI is superior in detection of tumor spread into the bone marrow. There is no clear advantage of CT or MRI for evaluation of nodal disease. Positron emission tomography (PET) is very sensitive for metastatic lymph nodes that are at least 8 mm in size and is the technique of choice in dubious cases. Imaging-guided biopsies are performed whenever needed. For imaging of treated head and neck cancer, PET scans have been found to generally offer higher sensitivity than MRI or CT. Combined PET/CT may be the modality of choice because it almost completely eliminates the false-positive and false-negative PET findings. Patients with head and neck cancer who are referred to tertiary care centers commonly arrive with cross-sectional images obtained at other institutions. Reinterpretation of these studies by dedicated radiologists frequently leads to changes in findings, which alter treatment and affect prognosis.     

不同影像检查对舌癌的诊断价值

目的：评估CT、MRI、PET-CT、超声术前预测舌癌范围的价值,并探讨影像上舌癌大小与淋巴结转移的关系,为临床治疗提供依据。方法：回顾性分析39例经病理证实的舌癌的影像资料,测量影像上病变直径,与术后病理对比,得到影像与病理直径最相符的检查,并判断病变直径与淋巴结转移之间的关系。结果：CT、MRI、PET-CT、超声均对舌癌部位显示良好,MRI、PET-C对显示舌癌侵犯范围具有一定优越性。与术后对比,MRI和PET-CT病灶范围均大于实体,MRI显示最接近实体,而CT对病灶显示小于实体。超声显示范围较实体小,对于病灶边界显示不如前三者。但能较好的显示肿瘤血供,对提示病变良恶性有一定帮助,MRI显示病灶平均直径≥2cm者,淋巴结转移率85.0%,〈2cm者淋巴结转移率仅为15.8%,P〈0.005,两者间有统计学差异。结论：MRI、PET-CT对于显示病灶范围优于CT和超声,并可预测淋巴结转移,但PET-CT费用昂贵,因此舌癌术前检查首选MRI。     

Paranasopharyngeal Space Involvement in Nasopharyngeal Cancer: Dectection by CT and MRI

Paranasopharyngeal tumour extension (PTE) from nasopharyngeal carcinoma (NPC) is staged in its own subgroup in the American Joint Committee on Cancer classification. Most large clinical trials use computed tomography (CT) to stage PTE, but diagnosis relies on indirect signs of tumour invasion such as asymmetry of the parapharyngeal fat. Magnetic resonance imaging (MRI) has the advantage of directly revealing PTE because of its ability to depict the complex anatomical structures that form the boundary of the nasopharynx. The aim of this study was to compare CT and MRI in the identification of PTE and to determine whether the imaging modality used influenced staging of the disease.The MRI and CT scans of 78 patients (156 parapharyngeal regions) with NPC were assessed for PTE. On MRI, PTE was considered to be positive when there was tumour invasion through the complex anatomical structures of the nasopharyngeal wall. When using CT, it was considered positive when there was: (1) distortion of the parapharyngeal fat plane; or (2) extension beyond a line drawn from the medial pterygoid plate to the lateral aspect of the carotid artery. CT scanning and MRI were compared.PTE was judged to be present in 28 of 78 (36%) patients by MRI and in 41 of 78 (53%) scanning by CT when using criterion 1 or 2. An analysis of the discordant findings revealed that MRI was positive in three sides of the nasopharynx in early tumour extension through the pharyngobasilar fascia but not identified with CT by using criterion 1 or 2. MRI was negative in 20 and 21 sides of the nasopharynx that were judged to be positive on CT by using criterion 1 and 2 respectively. In these patients MRI revealed that the positive CT scan was caused by a large tumour compressing but not invading the parapharyngeal fat space, a metastatic lateral retropharyngeal node, or a combination of the two.The imaging modality used for staging NPC has an impact on the staging of PTE. CT scanning suggested the presence of PTE more frequently than MRI because of its inability to distinguish the primary tumour from lateral retropharyngeal nodes, and direct tumour invasion of the parapharyngeal region from tumour compression. The imaging modality and criteria used for staging PTE should be taken into consideration when assessing the results of clinical studies.     

多层螺旋CT三维重建在骨肿瘤诊断中的临床价值

目的 探讨多层螺旋CT三维重建在骨肿瘤诊断中的临床价值.方法 选取80例骨肿瘤患者,先经多层螺旋CT三维重建技术诊断,后经MRI诊断.观察并记录2种诊断方式对骨肿瘤的确诊率,对恶性骨肿瘤临床分期确诊情况,评估多层螺旋CT三维重建技术对骨肿瘤的诊断价值.结果 多层螺旋CT三维重建的确诊率为88.8%,MRI确诊率为73.8%,多层螺旋CT三维重建的确诊率明显高于MRI(P＜0.05).采用多层螺旋CT三维重建对恶性骨肿瘤进行临床分期与病理、X线联合诊断结果无明显差异(P＞0.05).结论 多层螺旋CT三维重建技术可以准确诊断骨肿瘤病理性质,也能有效确诊恶性骨肿瘤的临床分期,为后续手术提供临床诊断依据.     

Paranasopharyngeal space involvement in nasopharyngeal cancer: detection by CT and MRI

Paranasopharyngeal tumour extension (PTE) from nasopharyngeal carcinoma (NPC) is staged in its own subgroup in the American Joint Committee on Cancer classification. Most large clinical trials use computed tomography (CT) to stage PTE, but diagnosis relies on indirect signs of tumour invasion such as asymmetry of the parapharyngeal fat. Magnetic resonance imaging (MRI) has the advantage of directly revealing PTE because of its ability to depict the complex anatomical structures that form the boundary of the nasopharynx. The aim of this study was to compare CT and MRI in the identification of PTE and to determine whether the imaging modality used influenced staging of the disease. The MRI and CT scans of 78 patients (156 parapharyngeal regions) with NPC were assessed for PTE. On MRI, PTE was considered to be positive when there was tumour invasion through the complex anatomical structures of the nasopharyngeal wall. When using CT, it was considered positive when there was: (1) distortion of the parapharyngeal fat plane; or (2) extension beyond a line drawn from the medial pterygoid plate to the lateral aspect of the carotid artery. CT scanning and MRI were compared. PTE was judged to be present in 28 of 78 (36%) patients by MRI and in 41 of 78 (53%) scanning by CT when using criterion 1 or 2. An analysis of the discordant findings revealed that MRI was positive in three sides of the nasopharynx in early tumour extension through the pharyngobasilar fascia but not identified with CT by using criterion 1 or 2. MRI was negative in 20 and 21 sides of the nasopharynx that were judged to be positive on CT by using criterion 1 and 2 respectively. In these patients MRI revealed that the positive CT scan was caused by a large tumour compressing but not invading the parapharyngeal fat space, a metastatic lateral retropharyngeal node, or a combination of the two. The imaging modality used for staging NPC has an impact on the staging of PTE. CT scanning suggested the presence of PTE more frequently than MRI because of its inability to distinguish the primary tumour from lateral retropharyngeal nodes, and direct tumour invasion of the parapharyngeal region from tumour compression. The imaging modality and criteria used for staging PTE should be taken into consideration when assessing the results of clinical studies.     

SPECT骨显像联合CT和MRI在恶性肿瘤骨转移诊断中的临床价值

目的探讨单光子发射计算机断层成像术(SPECT)骨显像联合CT和MRI在恶性肿瘤骨转移诊断中的应用价值。方法选取2016年3月至2019年3月间北京市房山区第一医院收治的80例恶性肿瘤并发骨转移患者,均采用SPECT骨显像、CT和MRI检查,分析原发肿瘤骨转移灶区域分布及三种检测方式诊断骨转移瘤的效能。结果无明显骨痛症状者46例,有明显骨痛症状者34例。骨转移瘤发生部位依次为脊柱、肋骨、骨盆、胸部、四肢和颅骨。脊柱转移瘤中,好发部位依次为胸椎、腰椎、骶椎和颈椎。SPECT与CT相同扫描野内诊断出464处病灶,SPECT检出429处(92.5%),CT检出率361处(77.8%),两者比较,差异有统计学意义(P<0.05),在相同扫描野之外SPECT另检出143处病灶。SPECT与MRI相同扫描野内诊断出321处病灶,SPECT检出307处(95.6%),MRI检出265处(82.6%),两者比较,差异有统计学意义(P<0.05),在相同扫描野之外SPECT另检出286处病灶。CT与MRI相同扫描野内诊断出259处病灶,CT检出185处(71.4%),MRI检出248处(95.8%),两者比较,差异有统计学意义(P<0.05)。SPECT骨显像联合CT和MRI检查的灵敏度、特异性和准确度均高于单独使用SPECT骨显像、CT或MRI,差异均有统计学意义(均P<0.05)。结论SPECT可作为可疑骨转移瘤的首选筛查手段,联合CT和MRI能明确恶性肿瘤骨转移的区域分布情况,提高诊断的灵敏度、特异性及准确度,有较高的临床价值。     

Giant adrenal pseudocyst: A rare diagnosis

We present a rare case of giant adrenal pseudocyst as a cause of right upper quadrant (RUQ) pain and highlight the typical multimodality imaging features. The case demonstrates the imaging features associated with giant adrenal pseudocysts to aid accurate and timely diagnosis. Despite the rarity of these lesions they are important to consider as benign lesions can closely mimic malignant ones. Unenhanced and contrast‐enhanced CT is the imaging of choice for adrenal cysts. However, MRI can provide more exquisite assessment of cystic, solid and enhancing components. Pseudocysts can be purely cystic, mixed or solid. Classically, adrenal pseudocysts are described as cystic lesions (of homogenous water density) with a fibrous wall and thin internal septations. Mural/septal calcification is commonly demonstrated due to haemorrhage, this is discernible from central/amorphous calcification seen in malignant disease. As in this case, pseudocysts can contain solid components or layering secondary to haemorrhage. The key to differentiating organised haematoma from tumour is the lack of enhancement. If serial imaging is undertaken in these patients rapid changes in the solid components may be seen reflecting resolving haematoma. Adrenal pseudocysts are rare and have a wide differential. Cystic adrenal lesions warrant multimodality assessment as their imaging features aid diagnosis and differentiation from malignant disease. We suggest that MRI plays a complimentary role to CT. CT is superior at demonstrating mural/septal calcification but MRI aids in determining cystic components and differentiating haemorrhage from tumour.     

CT and MR imaging in the evaluation and staging of lung cancer

Cancer of the lung is one of the most frustrating yet important challenges facing medicine today. Despite screening programs and education of the public concerning the established link of lung cancer and cigarette smoking, the overall incidence of lung cancer continues to rise. Improved imaging has led to more accurate staging. Expanded treatment has yielded improving survivals of certain specific tumors. Accurate diagnosis and staging of lung cancer is important in detecting therapy and prognosis. Computed tomography (CT) has been established as an important component of the staging process. More recently, applications of magnetic resonance imaging (MRI) are ideally suited to evaluate tumor extent and nodal disease. We reviewed the uses and limitation of CT and MRI. Compared with CT, the relatively low signal in the lung limits the detection of pulmonary nodules and other lung parenchymal diseases, and noise due to motion has been a frequent and significant problem in thoracic MRI. Because of its superior spatial resolution and ability to detect calcification, CT is better than MRI for the detection and evaluation of lung nodules and mediastinal adenopathy when assessing lung cancer. For the detection of mediastinal invasion or lymph node metastases, CT and MRI generally provide similar information. However, volume averaging problems, which may occur on trasaxial CT, can be avoided or clarified using MRI, and nodes can sometimes be more clearly distinguished from vessels using this technique. In the diagnosis of hilar masses or lymphadenopathy, CT and MR provide similar information in the majority of cases, but occasionally MR may more clearly indicate the presence or absence of a mass. Because of superb vascular imaging capability (without the need for exogenous contrast agents), exquisite soft tissue contrast, the ability to image the chest directly in multiple planes, and the potential to characterize certain tissues, MRI appears to be superior to CT in defining the extent of chest-wall invasion. In general, CT is superior to MRI as an all-around tool for imaging the wide range of thoracic abnormalities that can be present in patients with lung cancer. Limited availability, and longer examination time of MRI compared with CT has restricted the use of thoracic MRI. If MRI is used selectively as a secondary imaging study to answer specific questions raised or unanswered by CT, its value can be optimized.     

Magnetic resonance imaging of maxillary cancer--possibility of detecting bone destruction

The purpose of this study was to evaluate the detectability of bone destruction of maxillary cancer with magnetic resonance imaging (MRI) using 14 cases of squamous cell carcinoma of the upper jaw. The detectability of bone destruction including the degree of spread to adjacent soft tissues was evaluated and compared to that of clinical examination, computed tomography (CT) and conventional X-ray films. MRI could show bone destruction of each bony part almost equally with CT, but differentiation among simple bone defects, bone expansion and bone destruction was difficult on MRI. The pattern of bone destruction of alveolus that could be detected on conventional X-ray examinations, could not be assessed on either CT or MRI. Soft tissue infiltration of the tumour was more clearly detected on MRI compared with CT and conventional X-ray films.     

全身弥散加权成像在恶性肿瘤骨转移诊断中的应用

 目的　探讨全身弥散加权成像（WB-DWI）在恶性肿瘤骨转移诊断中的应用价值。方法　对118例恶性肿瘤患者行WB-DWI检查,并于扫描后1周内对可疑骨转移部位行常规磁共振成像（MRI）／CT检查。对资料进行统计学分析,比较单独应用WB-DWI、MRI／CT及二者联合应用（WB-DWI＋MRI／CT）对恶性肿瘤骨转移的诊断价值。分别测定骨转移组及良性骨病变组的表观弥散系数（ADC）值,探讨其在良恶性病变诊断中的价值。结果　受试工作者曲线（ROC）分析结果显示,WB-DWI＋MRI／CT诊断骨转移瘤的ROC曲线下面积、特异度、正确诊断指数及阳性预测值最高（0.999、100.0 %、97.4 %、100.0 %）,诊断效果最好;骨转移组平均ADC值[（0.71±0.15）×10-3 mm2／s]明显低于良性骨病变组[（1.50±0.23）×10-3 mm2／s],差异具有统计学意义（F＝261.587,P＜0.001）。结论　WB-DWI是常规MRI／CT的有益补充,结合ADC值测定,在恶性肿瘤骨转移诊断与鉴别诊断方面具有一定价值。     

Contribution of registered and/or fused images to radiotherapy]

The quality of treatment that one can realize today in conformal radiotherapy, can be reached only if one has access to 3D imaging allowing a precise determination of the volume of the organs at risk and of the GTV. For this reason, one has access to anatomical imaging, CT or MRI, and functional and metabolic imaging, PET or SPECT imaging. CT gives the electronic density of the tissues, which is essential to ensure a very precise calculation of dose distribution. Its insufficiency in the visualization of the tumour and some anatomical structures makes necessary the registration of these images with MRI of which distortions are sufficiently weak to be usable in radiotherapy. The registration will be usable only if images of each modality are realised with the patient in treatment position, except for brain, where only CT, on which is based the registration, must be done in treatment position. The images registration is also called images fusion by some authors. Others consider fusion of images as a way to display registered images on a screen, specially for CT images and PET, and MRI and SPECT. Nevertheless, the fusion of images is a function offered by some softwares. It allows obtaining a single volume of voxels from those of the registered images (CT and MR images). This volume is not usable in radiotherapy because it keeps only partially the contributions of the CT scan images and the MRI. At least, if one wants to visualize the active parts of a tumour or to make the difference between fibrosis and tumour left or recurrence after radiotherapy or chemotherapy, it is necessary to use PET or SPECT. To define correctly the CTV using these images, one must realize the anatomical localization of the metabolic abnormalities, which they highlight with a registration based on CT or MRI. The difficulties to obtain the registration of these images led the manufacturer to propose mixed machines allowing realizing, at the same time, a CT imaging and a PET or a SPECT imaging with the patient in treatment position.