CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) (USD $)	9 Months Ended
	Jan. 31, 2013	Jan. 31, 2012
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (21,331,000)	$ (31,237,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation	2,320,000	2,438,000
Depreciation and amortization	806,000	664,000
Amortization of discount on notes payable and debt issuance costs	0	33,000
Loss on early extinguishment of debt	1,696,000	0
Loss on disposal of property	8,000	2,000
Changes in operating assets and liabilities:
Trade and other receivables, net	370,000	(596,000)
Inventories, net	(1,024,000)	2,540,000
Prepaid expenses and other current assets, net	(83,000)	(285,000)
Other non-current assets	2,000	748,000
Accounts payable	(1,883,000)	(119,000)
Accrued clinical trial and related fees	(633,000)	750,000
Accrued payroll and related expenses	481,000	643,000
Deferred revenue	1,341,000	(3,174,000)
Customer deposits	1,864,000	704,000
Other current liabilities	(64,000)	(29,000)
Other long-term liabilities	(80,000)	(224,000)
Net cash used in operating activities	(16,210,000)	(27,142,000)
CASH FLOWS FROM INVESTING ACTIVITIES:
Property acquisitions	(686,000)	(1,103,000)
(Increase) decrease in other assets	(55,000)	34,000
Net cash used in investing activities	(741,000)	(1,069,000)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock, net of issuance costs of $885,000 and $1,007,000, respectively	26,166,000	26,190,000
Proceeds from issuance of notes payable, net of issuance costs of $251,000	14,749,000	0
Proceeds from exercise of stock options and under Employee Stock Purchase Plan	291,000	96,000
Principal payments on notes payable	(15,000,000)	(1,333,000)
Payment of final fee on notes payable	(975,000)	0
Principal payments on capital leases	(58,000)	(56,000)
Net cash provided by financing activities	25,173,000	24,897,000
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	8,222,000	(3,314,000)
CASH AND CASH EQUIVALENTS, beginning of period	18,033,000	23,075,000
CASH AND CASH EQUIVALENTS, end of period	26,255,000	19,761,000
Schedule of non-cash investing and financing activities:
Accounts payable for purchase of property	11,000	13,000
Fair market value of warrants issued in connection with notes payable	$ 470,000	$ 0