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Manipal University 2008-1st Sem B.E Biomedical Engineering VESTER END SEMESTER S – SUBJECT: MEDICAL IMAGE PROCESSING (BME-310 ) (REVISED CREDIT SYSTEM) - Question Paper

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VI SEMESTER B.E. DEGREE END SEMESTER exams – MAY 2008
SUBJECT: MEDICAL IMAGE PROCESSING (BME-310 )
(REVISED CREDIT SYSTEM)

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Reg. No.

MANIPAL INSTITUTE OF TECHNOLOGY

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INSPIRED BY LIFE

(A Constituent Institute of MU - Deemed University)

Manipal - 576 104

VI SEMESTER B.E. DEGREE END SEMESTER EXAMINATIONS - MAY 2008

SUBJECT: MEDICAL IMAGE PROCESSING (BME-310 )

(REVISED CREDIT SYSTEM)

Wednesday, May 28, 2008: 9.00 a.m.- 12.00 noon

TIME: 3 HOURS

MAX. MARKS: 100

Instructions to Candidates:

1. Answer any FIVE full questions.

2. Please answer to the point.

3. Draw labeled diagram wherever necessary

j (_xm+2 ⁿ )

^(a)

(b)

1.

Show that e

2

4

(c)

The mask associated with a 2D digital filter is sketched in Fig. 1.

(i) Sketch the output y(m,n) of the filter if the input input x(m,n) = 5(m,n).

(ii) Sketch the output image, if the input is: x(m,n) = 5(m+1,n+1) + 5(m-1,n-1). NOTE: Sketch your results on a 7*7 support (centered at the origin).

(iii) Is the filter causal? Is it a zero-phase filter? Justify your answers.

When would you resort to 2D linear filtering through FFT, instead of 2D convolution? Indicate the circumstances clearly.

is an eigen-function of a 2D (discrete) linear shift-invariant system. 6

2. (a) Find the output of the 3*3 median filter on the image in Fig. 2. 6

(b) Identify two advantages and two disadvantages of the filter in Q. 2 (a), as evident from 4 this example only (i.e., not general advantages and disadvantages).

x

x x x x

6

4

(c) Find the output of another median filter defined over the star-shaped neighborhood as sketched:

NOTE: the input to this median filter is the image in Fig. 2.

^(d) Write down your observations.

3 (_a) Explain concisely, the role of rods and cones in handling visual perception over a wide 6 range of intensities. Is the human visual system a linear device? Why, or why not?

(i) Find the result of applying the gray-level transformation T, sketched in Fig. 2 (a), on the image given in Fig. 3(b).

(ii) If the just-noticeable difference for a given observer is 3 units, what can you say ² about the effect of the transformation?

What are the four important properties of the discrete cosine transform (DCT) that ₄ makes it effective in image compression algorithms?

^(c)

4. ^(a) (b) ^(c) (d)

5. ^(a)

(b)

(i) Find the low-pass filter-mask and also the high-pass filter-mask associated with the

6

, hfb^:

3

hHFB =

" 1	1	1 "
8	8	8
1		1
	2
8		8
1	1	1
_ 8	8	8 _

(ii) Based on the sum of the values of the filter-coefficients, what can you say about the nature of the three filter-masks?

How would you compute and plot the magnitude of the 2D frequency-response of the filter, over a grid of size 512*512 using MATLAB? Note that the result must be properly centered. Indicate the important steps clearly (you need not write a program).

6

Explain briefly, the role of coincidence detection in PET.

3

What is beam-hardening? Why does it affect the quality of image reconstructed from X-ray projections?

2

Consider the transmission of an infinitesimally thin monochromatic X-ray beam of intensity Ii through a cross-section of the human body along a line parameterized by t and 9 (see Fig. 4). If I₀ is the intensity measured by a detector at the exit-point, deduce the relationship between the Ii, I₀ and the 2D distribution of attenuation /u(xy).

6

Consider an image consisting of a point of intensity (gray-level) 1, at (2,1) in the coordinate system as shown in Fig. 5.

(i) Sketch the projections of the image at 0⁰, 45⁰, 90⁰ and 135⁰ respectively.

8

(ii) Using the projections found in step (i), sketch the image obtained by backprojection only (i.e., no filtering is involved). The region-of-interest (ROI) is the same as that of the original image.

NOTE: You must clearly indicate the values of all the (i) coordinates involved, (ii) and

(ii) intensities (gray-levels) involved in the projections & in the backprojectedimage. NOTE: All the description in this question is in continuous coordinates.

(i) What are the effects (on the protons, and hence on the magnetic field associated with 4 them) of an RF excitation atLarmorfrequency, applied to a subject under the influence

of a uniform magnetic field? Indicate the reasons behind the effects.

6. (a) (b) ^(c) (d)

(ii) When would the RF excitation be called a 90^o excitation? ²

Consider tissues A and B under the influence of a uniform magnetic field: the value of T₁ associated with A is lower than that with B. If two 90⁰ RF pulses are applied in quick succession (i.e., within 500 ms), what would be the relative (i) strength and (ii) 6

frequency, of the signal due to tissue A - picked up by a coil in the vicinity, measured at the end of the second RF pulse? Justify your answer.

Write down the expressions for the two gradients to be applied simultaneously along orthogonal directions, to slice through the 2D Fourier transform of the image data at an 4 angle of 45⁰.

What are frequency- and phase-encoding gradients? 4