IMAGE REGISTRATION AND DATA FUSION TECHNIQUES

DESMOND PHECHUDI

OBJECTIVES INTRODUCTION DEFINITIONS

• CT• MRI• ECT• US

FUSION PRINCIPLES OF VARIOUS TECHNIQUES

• PET-CT• CT-MRI

COMPARISM CONCLUSION REFERENCE

INTRODUCTION• Medical imaging is the fundamental tool in conformal

radiation therapy. Almost every aspect of patient management involves some form of two or three dimensional image data acquired using one or more modality.

• Image data are now used for diagnosis and staging, for treatment planning and delivery and for monitoring patients after therapy.

DEFINITION OF TERMS• X-ray Computed

Tomography (CT)• A computerized tomography combines a series of images of

x-ray images taken from different angles and uses computer processing to create cross-sectional images or slices of the bones, blood vessels and soft tissue inside our body

Cont…• X-ray computed tomography (CT) provides the primary dataset for

most aspects of conformal therapy treatment planning. The data from CT are used to construct geometric and physical models of the patient. The geometric models are used to define anatomic structures, target volumes and to aid in radiation beam placement and shaping.

• The physical models provide density information required by most dose calculation algorithms. The planning CT dataset is also used to generate graphical aids such as beams-eye-view (BEV) displays and digitally reconstructed radiographs (DRRs) for planning and treatment verification.

• The major drawback of CT data is the limited soft tissue contrast, which can hinder accurate tissue discrimination.

Magnetic Resonance Imaging

• MRI is a technique that uses a magnetic field and radio waves to create detailed images of the organs and tissues within our body.

• Magnetic resonance imaging (MR) now plays an important role in treatment planning for several tumor sites, offering several advantages over CT. The excellent soft tissue contrast provided by MRI, permits better discrimination between normal tissues and many tumors (Khoo).

Cont…• A wide variety of MR imaging pulse sequences are available

that can improve image contrast by enhancing or suppressing specific tissues such as fat and conditions such as edema. Also, MR images can be directly acquired along sagittal and coronal planes, offering better visualization of certain tissues. While these features make MR an excellent choice as a primary dataset for treatment planning, several limitations have prevented the use of MR data alone.

• These drawbacks include the greater susceptibility of MR to spatial distortions and intensity artifacts, the lack of signal from cortical bone, and image intensity values that have no relationship to electron or physical density (Fraass, Schad).

Emission Computed Tomography (Nuclear

Medicine Imaging)• ECT is a type of tomography involving radioactive emissions• SPECT is a single photon emission computed tomography• PET positron emission tomography• SPECT and PET permit imaging of the transport and

accumulation of biologically active tracers.

• Examples of tracers for PET include 18F-deoxyglucose and 82Rb. and for SPECT include 131I and 99mTc.

Cont…

• SPECT and PET studies provide information about physiology rather than anatomy. The data from these modalities can provide important information about tumor metabolism and partial-volume tissue function.

• For patient monitoring, PET imaging has proven useful for discriminating between tumor recurrence and radiation necrosis (Doyle). For treatment planning SPECT data has been used to demonstrate regional lung function to help determine beam directions (Marks) and to quantify the distribution of radiolabeled mono-clonal antibodies (Koral).

Ultrasound• Ultrasound imaging uses mechanical (sound) energy rather than

electromagnetic energy to image tissue. Basically, ultrasound images tissue boundaries rather than internal structure. It can also be used to image blood flow. The major advantages of ultrasound are that images are produced in real-time, the required apparatus is relatively small, and it does not involve ionizing radiation.

• Three-dimensional data acquisition with ultrasound is now also possible. Together, these features have been exploited for radioactive source placement and boundary definition for prostate

• treatments (Narayana, Pathak).

• A disadvantage of ultrasound is that not all regions of the body, such as the brain and lung can be imaged effectively due to signal loss at large tissue density changes such as at tissue-bone and tissue-air interfaces.

Data Incorporation• The process of incorporating data from multiple imaging

studies into the treatment planning process involves two main tasks.

• The first task is to estimate the parameters of the coordinate transformation that relates homologous points in the two studies (data registration).

• The second task is to apply the resultant transformation to map structures or features of interest from one study to another (structure mapping) or to directly combine grayscale data from the two studies (data fusion).

Cont…Data registration & data fusion• Data Registration:– Geometric (and Photometric) alignment of one imagewith another– Images may be of same or different types (MR, CT, …)

• Data Fusion:– No single image modality provides a complete picturein all cases– images of different modalities & morecomprehensive story than provided by either

PRINCIPLES OF VARIOUS TECHNIQUES

PET-CT

• A combination of PET and CT to show body imaging

CT-MRI

• A combination of MRI and CT to show body imaging

PET-CT• While CT is excellent in depicting structures and anatomy, it

may miss small or early stage tumours, and, moreover, it does not provide any functional information on the tumours it detects.

• PET provides information on the metabolic function of organs or tissues by detecting how cells process certain compounds such as glucose but PET cannot pinpoint the exact size and location of tumours to the precision required for optimal diagnosis and treatment planning.

Cont• PET and CT obviously complement each other in providing

important diagnostic information.

• Separate PET and CT images are unfortunately difficult to fuse because the patient is generally not positioned identically on both machines.

• However, the recently introduced PET/CT machines, integrating PET and CT technologies into a single device, enable the collection of both anatomical and biological information simultaneously during a single examination, resulting in accurately fused PET and CT images that permit a more accurate tumour detection and tumour localization for a wide variety of cancers.

PET-CTAdvantages

Earlier diagnosis of disease;

Accurate staging and tumour

localization;

More precise treatment;

Monitoring of response to treatment

and early detection of recurrences;

Reduction of biopsy sampling errors;

Reduction of the number of invasive

procedures required during follow-

up.

Disadvantages

• Expensive• Side effects of radioactive

source

CT-MRICT shows bony structures – very accurate

MRI image volume: soft tissue, show presence of a tumour

Fusing the two volumes, to find the most probable image is the core of automed radiationtherapy planning

Click icon to add picture

CT-MRI

Advantages

• Better tumor delineation

• Spares normal tissue

• Better image quality

Disadvanyages

• Expensive• Time consuming

Benefits Of CT-MRIRegistration And Fusion In Tumor

Volume DelineationMethods. The image fusion software was applied to delineate 16 patients.The patients were scanned on CT and MRI in the treatmentposition within an immobilization device before the initialtreatment. The gross tumor volume (GTV) and clinical targetvolume (CTV) were delineated on CT alone and on CT+MRIimages consecutively and image fusion was obtained.

Results.Image fusion showed that CTV delineated on a CT imagestudy set is mainly inadequate for treatment planning, in comparisonwith CTV delineated on CT-MRI fused image study set. Fusion of different modalities enables the most accurate target volume delineation. Conclusion. This study shows thatregistration and image fusion allows precise target localizationin terms of GTV and CTV and local disease control.

CONCLUSION• A combination of imaging modality shows an

improved organ imaging which helps in conformal radiotherapy

• Image fusion between PET-CT and CT-MRI are useful in GTV and CTV determination in conformal radiotherapy thus sparing normal tissues.

• More research

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